Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Accelerated Capacity and Cycling Performance via Facile Instantaneous Precipitation Induced Amorphization for Lithium-Ion Batteries Reviewed International coauthorship

Yang W., Huang J., Zhang Y., Saito N., Zhang Z., Yang L.

Small Methods Vol. 7 ( 11 ) 2023.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Small Methods

Conversion-alloying anodes have garnered escalating attention with high theoretical capacity, however, they are seriously hindered by large volume distortion and capacity fading. To counter, structural modification needs more exploration. Herein, advantageous structure and high-performance are realized in new amorphous PbSb2O6 (PSO-a) nanosphere via facile instantaneous precipitation induced amorphization; conversion-alloying mechanism endows it with prominent lithium-storage capability; nanostructure can shorten ion-transfer distance and accommodate volume change outside the bulk of PSO-a; and loosely-stacked isotropic amorphous structure can enhance kinetics both at electrode/electrolyte interfaces and in the bulk. Volume change is synergistically stabilized from within to outside the bulk, leading to accelerated capacity and cycling. As expected, when employed in half-cells with 1 m LiPF6 in ethylene carbonate/diethyl carbonate/dimethyl carbonate/fluoroethylene carbonate (3:3:3:1 by mass) as electrolyte, glass microfiber filter as separator, and pure lithium foil as counter electrode, it realizes eminent performance with high specific capacity of 1512.6 mA h g−1 at 0.1 A g−1 and 755.1 mA h g−1 after 1000 cycles at 3 A g−1. To the best of the authors' knowledge, this is the first time PbSb2O6 is utilized as high-performance anode for lithium-ion batteries. Furthermore, this facile strategy provides a promising direction for high-performance amorphous anode material.

DOI： 10.1002/smtd.202300691

Correlation function of specific capacity and electrical conductivity on carbon materials by multivariate analysis Reviewed

Moon J., Yun H., Ukai J., Chokradjaroen C., Thiangtham S., Hashimoto T., Kim K., Sawada Y., Saito N.

Carbon Vol. 215 2023.11

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

An attention to a Li ion battery for electric vehicles has been attracted, but there are two huge problems: a short mileage and slow charging speed. Therefore, it is required to improve the specific capacity and electrical conductivity of the carbon material used for an anode and a conductive agent. To solve these problems, this study organized correlation analysis with descriptor vectors by collecting experimental properties including capacity and conductivity from 21 various types of carbon materials. Focusing on the flux of Li ion, it was found that the capacity was dependent on the intercalation of Li ions, which lead to propose the correlation equation based on the Hill equation. Furthermore, the intercalation occurred at the edge of basal plane lead an increase of the width of the gap between two graphene layers, followed by a diffusion through the basal plane, finally the expanded gap recovered its original width. Also, it was found that the variables which are sensitive to the conductivity are largely dependent on the defects and especially the number of graphene layers around the surface, which proposed a correlation equation that can predict the capacity and conductivity. To validate these functions, we checked the effectiveness of it with both experimental data from 27 previous studies and statistical method. As a result, it was confirmed enough to predict them. Finally, a candidate structure for improving the battery performance was proposed, thus our study aims to guide the exploration of electrode materials for LIBs.

DOI： 10.1016/j.carbon.2023.118479

Search for stable host materials as low-voltage anodes for lithium-ion batteries: A mini-review Reviewed International coauthorship

Zhang Y., Huang J., Saito N., Zhang Z., Yang L., Hirano S.i.

Energy Storage Materials Vol. 55 page： 364 - 387 2023.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Energy Storage Materials

The explosive demand for lithium-ion batteries (LIBs) in electric vehicles, portable electronics, and smart grids has spurred extensive research in recent years. The key to essential advances in LIBs depends on the search for stable host electrode materials with desirable energy and power densities. In the development of emerging stable host anode materials, the operating potential is an overlooked but crucial parameter because it deeply influences the energy, power, and safety of batteries. The ideal potential should not be too close to the lithium deposition potential like graphite (0.1 V vs. Li+/Li) which would trigger the formation of lithium dendrites under high rates, nor should be too high like spinel Li4Ti5O12 (> 1.5 V vs. Li+/Li) which compromises the batteries’ power and energy density. This mini-review firstly gives an account of several types of titanium-based and vanadium-based compounds as stable host anodes with the average operating potentials around or below 1 V vs. Li+/Li. The mechanisms for stable lithium storage and the origins of the low operating potentials are discussed by combining various characterization technologies. The key barriers and corresponding approaches are summarized for progressive electrochemical performance. Furthermore, several concise perspectives and challenges aiming at further theoretical prediction and practical application are provided.

DOI： 10.1016/j.ensm.2022.11.030

Nanoscale advanced carbons as an anode for lithium-ion battery Reviewed International coauthorship

Naraprawatphong R., Chokradjaroen C., Thiangtham S., Yang L., Saito N.

Materials Today Advances Vol. 16 2022.12

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today Advances

Nanoscale advanced carbons, including carbon nanotube, graphene, carbon nanosphere, porous carbon, and their derivatives, are represented as distinct types of material generate in various forms, structure dimensions, and properties. They feature a large specific surface area, excellent conductivity, high mechanical properties, tunable chemical functionality, and a broad potential window, which essentially require for lithium-ion battery systems. The nanoscale advanced carbons have been intensively researched and developed as a negative electrode component to improve battery performance. This review deliberately discusses structures, main properties, and synthesis methods that are directly related to the physical properties and chemical behaviors of the nanoscale advanced carbons. Moreover, currently good candidates for anode material for lithium-ion batteries were summarized. The importance of the primary function and the synergistic effect of nanoscale advanced carbons with active electrode species is emphasized. The systematic information from this review provides a promising tool that represents an essential reference for selecting anode electrode materials and designing the next generation of advanced lithium-ion batteries.

DOI： 10.1016/j.mtadv.2022.100290

Saccharide-originated fluorescent carbon dots synthesized by in-liquid plasma with controlled orderliness of carbon core through precursor alteration for selective and rapid metal ion detection Reviewed International coauthorship

Treepet S., Chokradjaroen C., Kim K., Saito N., Watthanaphanit A.

Materials Today Chemistry Vol. 26 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today Chemistry

Carbon dots (CDs) have grown interested in replacing metal-based quantum dots due to their fluorescent properties with low toxicity. The green synthesis, therefore, represents a contribution to this research field. Here, we demonstrate the synthesis of CDs from simple saccharides, including fructose, glucose, and sucrose, using an eco-friendly method—solution plasma (SP)—by applying plasma in the aqueous solution of the precursor. Variations and characterizations are conducted to understand the role or influence of each synthesis parameter, i.e. saccharide precursor's molecular structure, solution pH (2, 5, and 8), and post-treatment method (freeze-drying and heat-drying), in the materials' structure and fluorescent properties. Blue light-emitting CDs are prepared from all precursors of pH 5 and 8 through SP, followed by heat-drying. Results show that SP is responsible for the carbon core formation, and thus the precursor type affects the carbon core's orderliness. Heat-drying causes oxidation on the CDs' surface, whereby OH functional groups change to C=O. Among all samples, the CDs synthesized from fructose at pH 5 (Fru-CDs-5) perform the best photoluminescence property, having the highest quantum yield (QY) of 9.16% and exhibiting an outstanding ability to detect Fe3+ ions. This is the first attempt to evince the potential use of SP to synthesize CDs from natural carbon sources and obtain CDs exhibiting superior fluorescence properties without any doping and complex synthesis steps. In addition to offering a new synthetic approach, this work specifies the role of the SP and the effect of the saccharide's molecular structure, which is the most relevant synthesis parameters mandatory to obtain tailored CDs with precise control.

DOI： 10.1016/j.mtchem.2022.101139

Graphitic N-doped graphene via solution plasma with a single dielectric barrier Reviewed

Niu J., Chokradjaroen C., Saito N.

Carbon Vol. 199 page： 347 - 356 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Graphitic nitrogen-doped graphene (g-NG) with significantly high nitrogen content, i.e., 18.79 at.%, could be produced by the electrical discharge in liquid, so-called “solution plasma”, with a single dielectric barrier. The proposed system could reduce the excessive current, resulting in stabilizing the glow plasma and maintaining the overall temperature. It could promote the preservation of nitrogen atoms from evaporation during the synthesis process and the formation of a graphitic carbon framework. Moreover, the influence of the precursors, i.e., six-membered ring organic molecules with and without the substitution of nitrogen atoms and the nitrogen-based functional groups, was also investigated to provide the guideline for the synthesis of g-NG via this proposed method. The substitution of nitrogen atoms in the benzene ring could be used to synthesize g-NG with higher nitrogen dopants, compared to the benzene ring with only nitrogen-based functional groups.

DOI： 10.1016/j.carbon.2022.08.032

First-principles studies of enhanced oxygen reduction reactions on graphene- and nitrogen-doped graphene-coated platinum surfaces

Nam H.N., Phung Q.M., Choeichom P., Yamauchi Y., Saito N.

Physical Chemistry Chemical Physics Vol. 26 ( 14 ) page： 10711 - 10722 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Developing innovative platinum-based electrocatalysts and enhancing their efficiency are crucial for advancing high-performance fuel cell technology. In this study, we employed DFT calculations to provide a theoretical basis for interpreting the impact of graphene coatings on various Pt surfaces on oxygen reduction reaction (ORR) catalytic activity, which are currently applied as protective layers in experiments. We comprehensively assess the geometric and electronic properties of Pt(100), Pt(110), and Pt(111) surfaces in comparison to their graphene-coated counterparts, revealing different adsorption behaviors of O2 across these surfaces. The ORR mechanisms on different Pt surfaces show distinct rate-determining steps, with Pt(111) showing the highest ORR activity, followed by Pt(110) and Pt(100). Graphene coatings play a key role in enhancing charge transfer from the surface, resulting in modifications of O2 adsorption. Despite influencing ORR kinetics, these graphene-coated surfaces demonstrate competitive catalytic activity compared to their bare counterparts. Notably, Pt(111) with a graphene coating exhibits the lowest activation energy among graphene-coated surfaces. Our calculations also suggest that the ORR can occur directly on non-defective Pt@graphene surfaces rather than being restricted to exposed Pt centers due to point defects on graphene. Furthermore, our work highlights the potential of nitrogen doping onto the Pt(111)@C surface to further enhance ORR activity. This finding positions nitrogen-doped Pt@C as a promising electrocatalyst for advancing electrochemical technologies.

DOI： 10.1039/d4cp00269e

Nanoarchitectonics Solution Plasma Polymerization of Amino-Rich Carbon Nanosorbents for Use in Enhanced Fluoride Removal Reviewed International coauthorship

Tipplook M., Tanaka H., Sudare T., Hagio T., Saito N., Teshima K.

ACS Applied Materials and Interfaces Vol. 16 ( 6 ) page： 7038 - 7046 2024.2

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Amino-functionalized carbon (NH2C) is an effective adsorbent in removing pollutants from contaminated water because of its high specific surface area and electrical charge. In the conventional preparation method, the introduction of amino groups onto the carbon surface is limited, resulting in low pollutant adsorption. Herein, we present simultaneous carbonization and amination to form NH2C via electrical discharge of nonequilibrium plasma, and the resultant material is applied as an effective adsorbent in fluoride removal. The simultaneous process introduces numerous amino groups into the carbon framework, enhancing the adsorption efficiency. The fluoride adsorption capacity is approximately 121.12 mg g-1, which is several times higher than those reported in previous studies. Furthermore, computational modeling is performed to yield deeper mechanistic insights into the molecular-level adsorption behavior. These data are useful in designing and synthesizing advanced materials for applications in water remediation.

DOI： 10.1021/acsami.3c15172

Synthesis of crown-ether-embedded graphene by the solution plasma Reviewed International coauthorship

Kim H.m., Saito N., Kim D.w.

Carbon Vol. 216 2024.1

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

DOI： 10.1016/j.carbon.2023.118578

A solid-solution approach for high frequency 3-dimensional isotropic negative-refractive-index metamaterials based on microwave ceramics International coauthorship

Chang Q., Wang Z., Liu X., Saito N., Fan T.

Ceramics International Vol. 50 ( 1 ) page： 772 - 780 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramics International

Negative refraction has yielded valuable insights and solutions in electromagnetics. However, progress in this field has been hindered primarily by implementation challenges, including the limited availability of raw materials and assembly difficulties, particularly at high frequencies. In this paper, a novel flexible self-assembly method was proposed, through which a controllable solid solution of close-packed structures can be attained. By integrating the flexible self-assembly method with an all-dielectric left-handed material structure, a negative-refractive-index metamaterial (NRIM) model was conceived. Magnetism is not a prerequisite under this scheme; therefore, a demonstration based on a microwave dielectric ceramic was proposed, wherein two subdivisions of close-packed structures were studied. Analysis of the field distribution and electromagnetic eigenmodes using finite element analysis revealed a negative refraction band at around 20 GHz, with a relative bandwidth of 4.2%. The analysis of dispersion behavior verified spatial isotropism in the NRIM. In summary, the designed passive NRIM only requires moderate dielectrics and is isotropic in three dimensions, thus bearing a high resemblance to natural mediums.

DOI： 10.1016/j.ceramint.2023.10.158

Regulated Phase Separation in Al–Ti–Cu–Co Alloys through Spark Plasma Sintering Process Reviewed

Lee S., Chokradjaroen C., Sawada Y., Yoon S., Saito N.

Materials Vol. 17 ( 2 ) 2024.1

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al–Ti–Cu–Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al–Ti–Cu–Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8–5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

DOI： 10.3390/ma17020304

Conversion of fructose to 5-hydroxymethylfurfural using solution plasma process Reviewed International coauthorship

Klanarong N., Saito N., Prasertsung I., Damrongsakkul S.

Renewable Energy Vol. 218 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Renewable Energy

5-hydroxymethylfurfural (HMF), a key building block chemical derived from renewable lignocellulosic biomass, is used to produce a variety of derivatives for the biorefinery industry. In this work, the solution plasma process (SPP) was first applied to convert fructose, a key component from biomass, into HMF. Various conditions that affect fructose conversion and HMF yield were studied, including plasma treatment time (0–300 min), DMSO concentration (0–70%), electrode types (Iron; Fe and tungsten; W), system temperature (70–90 °C) and initial fructose concentration (10 g/L and 25 g/L). SPP was showed to enhance the conversion process to achieve high fructose conversion and HMF yield at the temperature (90 °C) lower than other conventional heating processes. The maximum fructose conversion and HMF yield were achieved at 95% and 76%, respectively at the DMSO concentration of 70% with Fe-electrodes, 90 °C of system temperature, 10 g/L of initial fructose concentration, 22.5 kHz of pulsed frequency and plasma treatment time of 240 min. Sulfuric acid formed from DMSO dissociation and Fe-nanoparticles from electrode erosion could effectively act as catalysts for the dehydration of fructose to HMF. SPP can be a high-potential tool for enhancing HMF production from the dehydration process in BCG economy.

DOI： 10.1016/j.renene.2023.119299

Highly durable graphene-encapsulated platinum-based electrocatalyst for oxygen reduction reactions synthesized by solution plasma process Reviewed

Park J.H., Kim K., Wang X., Huda M., Sawada Y., Matsuo Y., Saito N., Kawasumi M.

Journal of Power Sources Vol. 580 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Power Sources

Though expensive platinum (Pt) is used as catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), insufficient durability remains as a bottleneck for commercialization of PEFCs. Improving both catalytic performance and durability by graphene encapsulation is an attractive strategy to solve this problem. In this study, graphene-encapsulated PtFe core-shell catalyst is synthesized with dimethyl formamide (DMF) and a pair of Pt and Fe electrodes without using any metal salts by utilizing the solution plasma (SP) process. TEM and EELS results show synthesized PtFe nanoparticles are encapsulated with close to single-layered highly crystallized graphene. Although commercial Pt/C showed significant performance degradation (ECSA −33%, MA −68%) after 50,000 cycles of accelerated durability test (ADT), PtFe core-shell catalyst shows remarkably improved durability (ECSA −13%, MA −19%) while graphene shell clearly remains. The improved durability is more prominent in the single cell test, the decrease in maximum power density after 6000 cycles of ADT was significantly lower as −1.2%, compared to that of Pt/C (−52.1%). This study introduces a novel and attractive catalyst synthesis process by the SP method followed by heat treatments and suggests graphene encapsulation can improve long-term durability of catalyst while maintaining ORR activity.

DOI： 10.1016/j.jpowsour.2023.233419

Novel solution plasma synthesis of highly durable carbon shell encapsulated platinum-based cathode catalyst for polymer electrolyte membrane fuel cells Reviewed

Park J.H., Saito N., Kawasumi M.

Carbon Vol. 214 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Developing an effective method for synthesizing high-performance and durable catalysts for the oxygen reduction reaction is of great importance for cost reduction and the wide application of fuel cells. This study presents a simple and effective strategy using a plasma reaction in the liquid phase to synthesize carbon-shell-encapsulated Pt and PtFe catalysts. A carbon-shell-encapsulated PtFe catalyst alloyed with up to 29 at.% Fe exhibits a mass activity of 730 mA·mgpt−1 and a specific activity of 1772 μA cm−1, which are 2.4 and 5 times higher than that of commercial Pt/C, respectively. The carbon shell effectively maintained the low oxidation state of Pt by suppressing the formation of Pt–OH and significantly improved the durability of the catalyst in accelerated durability tests, increasing the gap in mass activity with Pt/C by a factor of up to six after 50,000 cycles. In addition, the decrease in the electrochemical surface area by the carbon shell enabled a more stable 4-electron reaction over a wide potential range. This study may provide fascinating insights into the effect of the carbon shell contributing to the improvement of the catalytic activity and durability of fuel cells as well as the novel plasma-based synthesis strategy of core-shell catalyst.

DOI： 10.1016/j.carbon.2023.118364

Preparation of lightweight, high hardness multi-component systems induced by partial oxidation and hard intermetallic phase formation Reviewed

Lee S., Chokradjaroen C., Sawada Y., Saito N.

Journal of Materials Research Vol. 38 ( 18 ) page： 4235 - 4246 2023.9

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Research

The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems were prepared by mechanical alloying in oxygen-lean atmosphere followed by spark plasma sintering. The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems which were sintered at 750 °C after 16 h milling showed the highest hardness of 509 and 947 HV with low densities of 2.9 and 3.9 g/cm3, respectively. The decrease in particle size and uniform dispersion of elements through optimization of the MA process induced the formation of uniform composite microstructure after SPS. Moreover, the addition of the fourth element, Cu, showed a significant impact on the improvement in hardness. This result was explained from the perspective of the microstructure and the electronic nature of elements. Our results provide a facile method for synthesizing oxide/metal composites from elemental powders without a separate oxidation process. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1557/s43578-023-01137-z

Cationic nitrogen-doped graphene coated silver as low-work function electrode for inverted perovskite solar cells Reviewed

Yokoyama K., Lin H.S., Shui Q.J., Wang X., Saito N., Matsuo Y.

Applied Physics Express Vol. 16 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

Interfacial layers (ILs) located between the cathode and electron transport layer (ETL) in inverted perovskite solar cells are commonly required to achieve high-performance devices. Therefore, it is essential to develop excellent IL materials to improve efficiency and stability. This paper introduces the graphene-based IL material, namely cationic nitrogen-doped graphene (CNG), and evaluates its performance on a methylammonium lead iodide (MAPbI3)-type inverted perovskite solar cells. The device with a CNG IL achieved a power conversion efficiency of 13.5%, which is higher than a state-of-the-art reference using bathocuproine IL. Mechanistic studies demonstrated that the CNG IL can (1) efficiently collect electrons from the lowest unoccupied molecular orbital of ETL by lowering the work function of the silver cathode, (2) improve the conductivity of the silver electrode for better electron transfer, and (3) smooth out the interface contact between ETL and cathode to reduce defects in the device. As a result, the CNG IL enhanced the inverted perovskite solar cells performance by simultaneously increasing the open-circuit voltage, short-circuit current density, and fill factor. Moreover, the unencapsulated CNG IL-applied device demonstrated good long-term stability, with 96% efficiency retained over 1000 h in nitrogen atmosphere at room temperature.

DOI： 10.35848/1882-0786/acea18

Introducing micropores into carbon nanoparticles synthesized via a solution plasma process by thermal treatment and their charge storage properties in supercapacitors Reviewed International coauthorship

Thu M.M., Chaiammart N., Jongprateep O., Techapiesancharoenkij R., Thant A.A., Saito N., Panomsuwan G.

RSC Advances Vol. 13 ( 24 ) page： 16136 - 16144 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Carbon materials synthesized via a solution plasma process (SPP) have recently shown great potential for various applications. However, they mainly possess a meso-macroporous structure with a lack of micropores, which limits their applications for supercapacitors. Herein, carbon nanoparticles (CNPs) were synthesized from benzene via SPP and then subjected to thermal treatment at different temperatures (400, 600, 800, and 1000 °C) in an argon environment. The CNPs exhibited an amorphous phase and were more graphitized at high treatment temperatures. A small content of tungsten carbide particles was also observed, which were encapsulated in CNPs. An increase in treatment temperature led to an increase in the specific surface area of CNPs from 184 to 260 m2 g−1 through the development of micropores, while their meso-macropore structure remained unchanged. The oxygen content of CNPs decreased from 14.72 to 1.20 atom% as the treatment temperature increased due to the degradation of oxygen functionality. The charge storage properties of CNPs were evaluated for supercapacitor applications by electrochemical measurements using a three-electrode system in 1 M H2SO4 electrolyte. The CNPs treated at low temperatures exhibited an electric double layer and pseudocapacitive behavior due to the presence of quinone groups on the carbon surface. With increasing treatment temperature, the electric double layer behavior became more dominant, while pseudocapacitive behavior was suppressed due to the quinone degradation. Regarding cycling stability, the CNPs treated at high temperatures (with a lack of oxygen functionality) were more stable than those treated at low temperatures. This work highlights a way of introducing micropores into CNPs derived from SPP via thermal treatment, which could be helpful for controlling and adjusting their pore structure for supercapacitor applications.

DOI： 10.1039/d3ra02314a

Morphological Evolution of Gold Nanoparticles Synthesized via Solution Plasma Sputtering: Effect of Sodium Chloride Concentration and Storage Time Reviewed International coauthorship

Chantaramethakul J., Choophun N., Chokradjaroen C., Watthanaphanit A., Saito N., Panomsuwan G.

Journal of Physical Chemistry C Vol. 127 ( 6 ) page： 3184 - 3193 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Morphological control of gold nanoparticles (AuNPs) is vital for tuning their optical, chemical, physical, and catalytic properties for desired specific applications. Despite numerous efforts dedicated in recent years, controlling the morphology of AuNPs synthesized via solution plasma sputtering (SPS) remains a challenge, requiring further investigation. Herein, AuNPs were synthesized via SPS in sodium chloride (NaCl) solutions of various concentrations (0.5, 1, 2, and 5 mM). Evolutions of localized surface plasmon resonance and morphology of AuNPs over a 30 day storage period were thoroughly examined using ultraviolet-visible spectroscopy and field-emission transmission electron microscopy. The formation and growth mechanisms of AuNPs during and after synthesis provide more insights into this nascent field. At the initial storage time, AuNPs with chain-like structures were observed at all the NaCl concentrations. Their size tended to increase from 6 to 10 nm with a broader size distribution with increasing NaCl concentration. At a prolonged storage time of 15 days, AuNPs became smaller and more isolated at all NaCl concentrations owing to the oxidative etching effect. After 30 days of storage, the number of Au ions dissolved from etching slowly reduced and grew on the AuNPs, affording increased particle sizes. The interplay between etching and growth processes proceeded until reaching equilibrium. AuNPs exhibited good colloidal stability at low NaCl concentrations (i.e., 0.5, 1, and 2 mM); however, coalescence and sedimentation occurred at a high NaCl concentration of 5 mM owing to a considerable reduction in the electrical double-layer thickness. These results demonstrated that the NaCl concentration and storage time crucially affect the morphological evolution and stability of AuNPs synthesized via SPS.

DOI： 10.1021/acs.jpcc.2c06474

A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment Reviewed International coauthorship

Back S., Saito N., Lee S.

Journal of Environmental Chemical Engineering Vol. 11 ( 1 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Environmental Chemical Engineering

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 ?s, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.

DOI： 10.1016/j.jece.2022.109075

Carbon Fibers Prepared via Solution Plasma-Generated Seeds Reviewed

Romero Valenzuela A.E., Chokradjaroen C., Choeichom P., Wang X., Kim K., Saito N.

Materials Vol. 16 ( 3 ) 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

Carbon fibers are materials with potential applications for CO2 capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when organic precursors are used. During the discharge and formation of carbon materials in solution, a soot product-denominated solution plasma-generated seeds (SPGS) is simultaneously produced at room temperature and atmospheric pressure. Here, we propose a preparation method for carbon fibers with different and distinctive morphologies. The control over the morphology is also demonstrated by the use of different formulations.

DOI： 10.3390/ma16030906

Effect on percolation threshold of catalytic layer: Pt/N-Doped graphene shell onto SWCNT for ORR electrode Reviewed

Dechojarassri D., Wang X., Chae S., Sawada Y., Hashimoto T., Saito N.

Fuel Cells Vol. 23 ( 1 ) page： 4 - 14 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Fuel Cells

A high-rate oxygen reduction reaction (ORR) is necessary for polymer electrolyte membrane fuel cells (PEMFC). In this work, by using a solution plasma technique, Pt catalytic particles coated with N-doped graphene (Pt-NG) were effectively produced at 25°C. According to transmission electron microscope images, the average diameter of Pt particles was 4 nm, while the graphene layer thickness was less than 1 nm. A catalytic layer of Pt-NG supported on single-walled carbon nanotubes (Pt-NG/SWCNT) was synthesized. Cyclic voltammetry was used to assess the ORR characteristics of Pt-NG/SWCNT catalytic layers. Only at a density of SWCNT to solvent ratio of 0.75 mg ml−1 were the ORR peaks clearly visible. Because of the high resistivity of SWCNT layers, the ORR peaks in other ranges, 0.4 mg ml−1 to 2.0 mg ml−1, were not clearly observed. The effect of SWCNT concentration on conductivity was proven to follow the basic concept of the percolation threshold.

DOI： 10.1002/fuce.202200020

Low-potential and high-capacity lithium battery anode based on hierarchical assemblies of Na<inf>2</inf>TiSiO<inf>5</inf> nanotubes Reviewed International coauthorship

Zhang Y., Huang J., Saito N., Zhang Z., Yang L., Hirano S.i.

Applied Surface Science Vol. 604 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

Titanium-based materials such as TiO2 and Li4Ti5O12 are promising candidates for next-generation lithium-ion batteries (LIBs), but the high operating potential and unsatisfactory specific capacity severely restrict the potential application prospects. Li2TiSiO5 as a novel anode has attracted great attention due to its low-potential and high-capacity properties, but the conversion transition of Li2TiSiO5 to Li4SiO4 and TiO during Li+ intercalation and de-intercalation unfavorably affects the structural stability and hinders Li+ transport. Herein, novel cocoon-like microspheres assembled by Na2TiSiO5 nanotubes (NTSO-T), as the substitute of Li2TiSiO5, are facilely synthesized through a hydrothermal reaction. The hierarchical structure could effectively facilitate the Li+ diffusion, reduces internal strain, and enhances structural stability without greatly reducing the tap density. With a low but safe operating potential of 0.75 V, NTSO-T anode exhibits a high reversible capacity of 400 mAh g−1 which exceeds most reported Ti-based anodes, and durable long-cycling performance (capacity retention after 3000 cycles reaches 77%). Most importantly, the rate capability of NTSO-T is significantly enhanced. Kinetic reaction analysis has demonstrated the pseudocapacitive contribution in NTSO-T anode dominates the lithium storage kinetics. In addition, ex situ XRD and Raman analysis reveal a partially reversible conversion mechanism occurring in the framework. The excellent electrochemical performance of NTSO-T provides a promising anode candidate for next-generation LIBs.

DOI： 10.1016/j.apsusc.2022.154409

Multi-strategy synergistic in-situ constructed gel electrolyte-binder system for high-performance lithium-ion batteries with Si-based anode Reviewed International coauthorship

Zhao E., Luo S., Zhang Z., Saito N., Yang L., Hirano S.i.

Electrochimica Acta Vol. 434 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

Silicon-based material have been considered as the most competitive candidate for next-generation anode in lithium-ion batteries (LIBs) due to its high specific energy density, natural abundance and attractive operating voltage. However, silicon-based anodes generally undergo significant volume changes and structural collapse during cycling, resulting in limited battery lifespan. Herein, a multi-strategy optimized in-situ gel electrolyte-binder system (GEBS) is rationally constructed, and electrochemical performances of the LIBs with Silicon-Graphite (Si-Gr) anodes are systematically evaluated by half-cell and full-cells. The in-situ generated polymer skeleton and improved interfacial compatibility of the GEBS effectively preserve the electrode structural integrity. Compared with the commercial liquid electrolyte, the volume change of the anode cycled with GEBS is suppressed from 208 % to 126 %. Benefiting from these merits, the full-cell with LiFePO4 cathode displays stable cycling stability with the capacity retention of 96.8 % after 260 cycles. Besides, the reversible capacity of the LiNi0.6Co0.2Mn0.2O2║Si-Gr full-cell is as high as 121.7 mAh g−1 after 200 cycles (capacity retention of 85.1 %), and the GEBS also exhibits obvious dominance at 55°C. This contribution effectively integrates multiple optimization strategies for Si-based anode and provides a feasible solution to address the challenge of its practical application in LIBs.

DOI： 10.1016/j.electacta.2022.141299

Remediation of water contaminated with polycyclic aromatic hydrocarbons using liquid phase plasma: Influence of electrical discharge condition

Kim U.J., Saito N., Lee S.H.

Frontiers in Marine Science Vol. 9 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers in Marine Science

Although the number of vessels with exhaust gas cleaning systems (EGCSs or scrubbers) has sharply increased to comply with strengthened regulations for marine environment, secondary pollutions are caused by discharged polycyclic aromatic hydrocarbons (PAHs) from scrubber effluent. Here, liquid-phase plasma (LPP) is employed to remediate water contaminated with PAHs. The increased frequency and pulse width enhanced the degradation efficiency, and 93.3, 90.7, 86.0, and 85.4% for naphthalene (Nap), acenaphthene (Ace), fluorene (Flu), and phenanthrene (Phe), respectively, are degraded at a frequency of 30 kHz and pulse width of 3 μs in 10 min. Considering physical condition of the plasma, long pulse width accelerated electrons, leading to increased generation of active species from intensified collision between electrons and surrounding molecules. Conversely, high frequency decelerated electrons due to the excessive changes in the polarity. However, the increased number of plasma discharges results in the generation of numerous active species. Generations of •OH and O radicals are confirmed by optical emission spectrometry and electron paramagnetic resonance. In addition, changes in functional groups which are corresponding to hydroxyl and oxygen groups are identified by Fourier transform infrared spectroscopy. Total PAHs in real scrubber are reduced from 1.1 to 0.4 μgL-1 with degradation efficiency of 63.6% after 10 min of LPP treatment. This study suggests LPP can be a promising method to protect diverse aqueous environments and provides optimal electrical discharge condition for degradation of organic pollutants.

DOI： 10.3389/fmars.2022.1033962

Hierarchical Porous Carbon Fibers Synthesized by Solution-Plasma-Generated Soot Deposition and Their CO<inf>2</inf> Adsorption Capacity

Romero Valenzuela A.E., Chokradjaroen C., Thiangtham S., Saito N.

Coatings Vol. 12 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings

Global warming caused by CO2 emissions is a major environmental problem. Thus, the development of materials with innovative architectures that approach the CO2 problem is a necessity. In this study, hierarchical porous carbon fibers (HCFs) were synthesized by a chemical deposition process that operates at 400 °C and uses solution-plasma-generated soot (PGS) as a carbon precursor. Subsequently, the CO2 adsorption capacity of the synthesized material was evaluated. The HCFs showed enhanced surface areas and networks of micropores and mesopores. Moreover, the HCFs were post treated by metal etching and KOH activation. The post treated HCFs achieved a CO2 uptake of 0.8 mmol g−1 at 273 K, which was superior to the simultaneously produced solution plasma carbon (SPC), which has a CO2 uptake of 0.2 mmol g−1.

DOI： 10.3390/coatings12111620

Plasma–Solution Junction for the Formation of Carbon Material

Niu J., Chokradjaroen C., Sawada Y., Wang X., Saito N.

Coatings Vol. 12 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs to be urgently explored to achieve the modulation of the SPP. Here, to address the knowledge gap, we experimentally determined the physical parameters of the spital distribution in the plasma phase, plasma–gas phase, and gas–liquid phase of the SPP by the Langmuir probe system with modification. Based on the assumption that plasma can act similarly to semiconductors with the Fermi level above the vacuum level, an energy band diagram of the plasma–solution junction could be proposed for the first time. It was observed that the Fermi level of the organic molecule could determine the magnitude of electron temperature in plasma, i.e., benzene produced the highest electron temperature, followed by phenol, toluene, and aniline. Finally, we found that the electron temperature at the interface could induce quenching, leading to the formation of multilayer large-size-domain carbon products. It provided significant evidence for achieving nonequilibrium plasma modulation of carbon nanomaterial synthesis.

DOI： 10.3390/coatings12111607

Layered Perovskite Lithium Yttrium Titanate as a Low-Potential and Ultrahigh-Rate Anode for Lithium-Ion Batteries

Zhang Y., Huang J., Saito N., Yang X., Zhang Z., Yang L., Hirano S.i.

Advanced Energy Materials Vol. 12 ( 31 ) 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Energy Materials

Graphite, as the dominant anode for commercial lithium-ion batteries, features sluggish electrochemical kinetics and low potential close to lithium deposition, leading to poor rate capability and safety issues. Although titanium-based oxides have received considerable attention, each alternative demonstrates unsatisfactory trade-offs between capacity, operating potential, rate capability, and lifespan. Here, submicrometer-sized lithium yttrium titanate (LYTO) is synthesized through facile sol–gel and ion-exchange reactions. With an average operating potential of 0.3 V versus Li+/Li, the LYTO anode demonstrates a high specific capacity of 236 mAh g–1 and durable cycling performance of 98% capacity retention after 3000 cycles. Impressively, without additional modification, a high-rate capability is achieved under a current density range from 0.5 C to 100 C (1 C = 200 mA g–1), e.g., delivering 112 and 87 mAh g–1 at 60 C and 100 C, respectively. Comprehensive characterizations and computational simulations reveal reversible solid-solution reactions occurring in the LYTO framework with little lattice change and fast 2D Li+ mobility achieved due to a low diffusion energy barrier. After incorporation with a LiFePO4 cathode, the energy density of the as-fabricated full cell reaches 2.4 times that of Li4Ti5O12/LiFePO4 full cell. The double characteristics of LYTO provide a fresh identification for high-performance anodes.

DOI： 10.1002/aenm.202200922

A non-flammable, flexible and UV-cured gel polymer electrolyte with crosslinked polymer network for dendrite-suppressing lithium metal batteries

Gu Y., Yang L., Luo S., Zhao E., Saito N.

Ionics Vol. 28 ( 8 ) page： 3743 - 3759 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Ionics

A flexible, non-flammable gel polymer electrolyte (GPE) was synthesized by combining UV-cured polymerization of ethoxylated trimethylolpropane triacrylate (ETPTA) within the framework of glass fiber (GF) membrane. Non-flammable hydrofluoroether (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, FEPE) and high flash point solvent (fluoroethylene carbonate, FEC) were employed as plasticizers for GPE-FEC/FEPE (60:40) to promote the safety of electrolyte and improve the compatibility with lithium metal anode. Non-flammable GPE-FEC/FEPE (60:40) possessed high safety level, high ionic conductivity (1.57 mS cm−1 at 30 °C), excellent oxidation stability (4.6 V vs. Li/Li+), high lithium-ion transference number (0.71) and good thermal stability (120 °C). After 1000 h test, Li/GPE-FEC/FEPE (60:40)/Li displayed better compatibility with lithium metal electrode compared with commercial liquid electrolyte. The test of Li/LFP cells showed that the safe GPE-FEC/FEPE (60:40) had excellent cycling performance at room temperature and elevated temperature. After 1000 cycles at 2 C and room temperature, the capacity retention was as high as 88.4%. XPS spectra proved that GPE-FEC/FEPE (60:40) was beneficial to promote the formation of LiF-rich SEI film on the surface of lithium metal anode, which could effectively inhibit the growth of lithium dendrites.

DOI： 10.1007/s11581-022-04621-4

Nitrogen-doped 3D porous graphene coupled with densely distributed CoO<inf>x</inf> nanoparticles for efficient multifunctional electrocatalysis and Zn-Air battery

Zhao Y., Wang X., Guo X., Shi N., Cheng D., Zhou H., Saito N., Fan T.

Electrochimica Acta Vol. 420 2022.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

Highly efficient and low-cost multifunctional electrocatalysts play a crucial role in energy storage and conversion systems. Herein, a new strategy is developed based on a structured precursor to design and fabricate a hierarchical porous nitrogen doped graphene coupled with densely distributed CoO/Co3O4 heterostructure that exhibits outstanding multifunctional activities. With rational hybridization of graphene and bimetallic nanoparticles, the as-obtained NGPC@CoOx integrated densely distributed CoO/Co3O4 active nanoparticles to 3D interconnected hierarchical N-doped graphene mesh, which gives rise to a multifaceted capability for electron/ion transfer and redox catalyzing. The NGPC@CoOx possesses excellent durability with a superior E1/2 of 0.86 V for oxygen reduction reaction (ORR), and a relatively low potential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of 1.61 V, and -0.162 V at 10 mA cm−2, respectively. Additionally, the superior cycling durability and high power density of NGPC@CoOx-based zinc-air batteries (184.4 mW cm−2) further confirm the potential application of prototype devices. This work introduces a new perspective on developing efficient multifunctional electrocatalysts with a well-designed 3D structure anchored with densely distributed nanoparticles towards energy storage and conversion technologies.

DOI： 10.1016/j.electacta.2022.140432

Fundamentals of solution plasma for advanced materials synthesis Reviewed International coauthorship

Chokradjaroen C., Wang X., Niu J., Fan T., Saito N.

Materials Today Advances Vol. 14 2022.6

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today Advances

Solution plasma is an atmospheric nonequilibrium plasma generated by electrical discharge in liquid phase at room temperature. The plasma configurations, solutions, electrode materials, as well as the characteristics of the power supply can be easily tuned. Due to these features of the solution plasma, various sizes, shapes, compositions of products can be controlled, leading to the effective utilization in several applications, such as a novel catalyst for energy conversion. To accomplish the use of solution plasma as a promising tool for the synthesis and modification of advanced materials, fundamentals and applied knowledge related to the solution plasma should be reviewed and discussed. Therefore, in this review, fundamentals of plasma in liquid are explained relating to the solution plasma, and detailed advanced applications of solution plasma are organized. It is expected to give powerful knowledge to guide the researchers in designing plasma conditions and synthesizing catalysts for different applications in the future.

DOI： 10.1016/j.mtadv.2022.100244

Design of three-dimensional isotropic negative-refractive-index metamaterials with wideband response based on an effective-medium approach

Chang Q., Liu X., Wang Z., Saito N., Fan T.

Applied Physics A: Materials Science and Processing Vol. 128 ( 5 ) 2022.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics A: Materials Science and Processing

Negative-refractive-index metamaterials (NRIMs) can provide opportunities for many new applications, but they are difficult to manufacture, especially when forced to work at high frequencies and required to be three-dimensionally isotropic. By integrating an effective-medium approach into all-dielectric left-handed materials (LHMs) and utilizing self-assembly, we developed a method to design three-dimensional NRIMs that can work in high frequencies and are suitable for mass production. The NRIMs are composed of arrays of spheres that are made from artificial media, which are devised under the effective-medium method in advance. Two cases with different close-packed structures were studied for verification purposes. Finite element analysis showed that both cases can achieve negative refraction within 14.5–15.2 GHz (Ku band), which qualifies as wideband. Negative refraction was further confirmed by investigating the resonance mode of units in each model. Dispersion analysis demonstrated isotropism and consistent behaviors in all cases, indicating the robustness of these properties over disorder accompanied by self-assembly. The proposed NRIM model is intrinsically isotropic, three-dimensional, passive, mass-producible, machinable and thus readily applicable.

DOI： 10.1007/s00339-022-05573-2

Flexible, solid-state, fiber-network-reinforced composite solid electrolyte for long lifespan solid lithium-sulfurized polyacrylonitrile battery

Luo S., Zhao E., Gu Y., Saito N., Zhang Z., Yang L., Hirano S.i.

Nano Research Vol. 15 ( 4 ) page： 3290 - 3298 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Nano Research

Solid lithium-sulfur batteries (SLSBs) show potential for practical application due to their possibility for high energy density. However, SLSBs still face tough challenges such as the large interface impedance and lithium dendrite formation. Herein, a high-performance SLSB is demonstrated by using a fiber network reinforced Li6.75La3Zr1.75Ta0.25O12 (LLZTO) based composite solid electrolyte (CSE) in combination with sulfurized polyacrylonitrile (SPAN) cathode. The CSE consisting of an electrospun polyimide (PI) film, LLZTO ionically conducting filler and polyacrylonitrile (PAN) matrix, which is named as PI-PAN/LLZTO CSE, possesses high room-temperature ionic conductivity (2.75 × 10−4 S/cm), high Li+ migration number (tLi+) of 0.67 and good interfacial wettability. SPAN is utilized due to its unique electrochemical properties: reasonable electronic conductivity and no polysulfides shuttle effect. The CSE enables a highly stable Li plating/stripping cycle for over 600 h and good rate performance. Moreover, the assembled SLSB exhibits good cycle performance of accomplishing 120 cycles at 0.2 C with the capacity retention of 474 mAh/g, good rate properties and excellent long-term cycling stability with a high capacity retention of 86.49% from 15th to 1,000th cycles at 1.0 C. This work rationalizes our design concept and may guide the future development of SLSBs. [Figure not available: see fulltext.]

DOI： 10.1007/s12274-021-3981-z

Solution plasma process for synthesizing polydiacetylene materials: Toward industrial utilization of colorimetric sensors

Saymung R., Watthanaphanit A., Saito N., Traiphol N., Traiphol R.

Journal of Industrial and Engineering Chemistry Vol. 106 page： 243 - 252 2022.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Industrial and Engineering Chemistry

A new route for synthesizing polydiacetylene (PDA) is introduced. Plasma is generated in a liquid matrix through a pair of electrodes, producing the excited atomic or molecular species, radicals, and UV radiation. The products of solution plasma process (SPP) act as initiators to induce polymerization of diacetylene monomers. Our results demonstrate that irreversible thermochromic PDA and reversible thermochromic PDA/Zn2+/ZnO nanocomposite can be effectively synthesized. The addition of ethanol significantly increases the polymerization rate. These PDA materials can be fabricated into paper-based colorimetric sensors for detecting volatile organic solvents, acids, bases, and surfactants. This synthetic pathway could be applied for industrial-scale applications.

DOI： 10.1016/j.jiec.2021.10.035

Morphology control of ZnO nanostructures using Zn and W electrodes in solution plasma process

Kim K., Chae S., Masuda Y., Saito N.

Materials Letters Vol. 309 2022.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Letters

The morphology of ZnO nanostructures was controlled by the type of electrodes used, without chemical additives in the solution plasma process. Nanorod and nanosheet-type ZnO were synthesized using Zn and W electrodes, respectively. In the solution plasma process, the ZnO nanostructure can be fabricated because of the unique reaction between ions and radicals at the plasma/liquid interface. During this reaction, ions generated from the metal electrode influence the morphology of ZnO by adsorption on the (0 0 1) facet. Zn(OH)42− ions promoted crystal growth in the [0 0 1] direction, resulting in a rod structure. In contrast, the sheet structure was formed owing to the inhibition of growth in the [0 0 1] direction by WO42− ions.

DOI： 10.1016/j.matlet.2021.131349

Synthesis of nitrogen-doped carbons from single-source precursors by solution plasma

Gasidit Panomsuwan, Chayanapat Chokradjaroen, Nagahiro Saito

Nanomaterials via Single-Source Precursors: Synthesis, Processing and Applications page： 475 - 505 2022.1

Language：English Publishing type：Part of collection (book)

Solution plasma processing is a bottom-up synthetic approach that can be employed for directly preparing nitrogen-doped carbons from single-source precursors with in situ nitrogen doping. Research efforts and interest in this topic have gained at a significant pace over the past years. This chapter provides an overview of solution plasma processing and recent progress on the synthesis of nitrogen-doped carbons from single-source precursors using this approach. The chapter starts by introducing the basic fundamentals of solution plasma and how to apply it in the synthesis of nitrogen-doped carbons. The effects of a solution plasma conditions and the type of precursors on the overall properties of nitrogen-doped carbons are summarized based on the important findings reported in the literature. A potential application of nitrogen-doped carbons as metal-free electrocatalysts for oxygen reduction reaction is explained and discussed in brief. At the end of the chapter, the remaining challenges and future prospects are highlighted for use in further studies. This chapter is intended to be generally informative and a useful guide for researchers who are new to this field.

DOI： 10.1016/B978-0-12-820340-8.00019-8

Asymmetric Porous and Highly Hydrophilic Sulfonated Cellulose/Biomembrane Functioning as a Separator in a Lithium-Ion Battery

Thiangtham S., Saito N., Manuspiya H.

ACS Applied Energy Materials 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Energy Materials

Biomembranes based on sulfonated cellulose (SC) blended with PLA/PBS composites were fabricated with different SC contents into polymer matrices. The obtained membranes were applied as separators in lithium-ion batteries (LIBs). The porosities of SC/biomembranes with 0.5, 1, and 2 wt % SC contents were estimated to be 66.6, 73.4, and 87.7%, respectively, which are significantly greater than that of the Celgard 2400 membrane, a commercial monolayer polypropylene (PP) separator membrane (42.1%). Due to its high porosity, hydrophilicity, and good interfacial compatibility with electrodes, the SC/biomembranes offer high electrolyte uptake and low interfacial resistance, leading to enhanced ionic conductivity. The cell with the 2 wt % SC/biomembrane also exhibited stable cycle performance and improved rate capacity, especially when discharged at the 0.2C rate. A 106 mAh/g capacity retention rate was achieved for a battery with the 2 wt % SC/biomembrane after 100 cycles at the 1C rate; meanwhile, the Celgard 2400 membrane exhibited a capacity of 81 mAh/g. These results show that SC has great innovative potential for use as a biofiller in biomembranes, which is suitable for LIB applications.

DOI： 10.1021/acsaem.2c00602

Au nanoparticle-decorated TiO<inf>2</inf>hollow fibers with enhanced visible-light photocatalytic activity toward dye degradation

Panomsuwan G., Wongcharoen S., Chokradcharoen C., Tipplook M., Jongprateep O., Saito N.

RSC Advances Vol. 12 ( 1 ) page： 193 - 200 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

TiO2 hollow fibers (THF) were prepared by a template method using kapok as a biotemplate and subsequently decorated by plasmonic Au nanoparticles using a solution plasma process. The THF exhibited an anatase phase and a hollow structure with a mesoporous wall. Au nanoparticles with a diameter of about 5-10 nm were uniformly distributed on the THF surface. Au nanoparticles-decorated TiO2 hollow fibers (Au/THF) have enhanced photocatalytic activity toward methylene blue degradation under visible light-emitting diode (Vis-LED) as compared to pristine THF and P25. This could be attributed to combined effects including effective light-harvesting by a hollow structure, large surface area due to a mesoporous wall of THF, and visible-light absorption and efficient charge separation induced by Au nanoparticles. The Au/THF also showed good recyclability and separation ability.

DOI： 10.1039/d1ra07323k

Synergetic design of dopant-free defect-enriched 3D interconnected hierarchical porous graphene mesh for boosting oxygen reduction reaction

Zhao Y., Wang X., Guo X., Cheng D., Zhou H., Saito N., Fan T.

Carbon Vol. 184 page： 609 - 617 2021.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

To resolve Pt-dependency problems in energy convention systems, we provide an idea for construct a highly active 3D interconnected hierarchical porous graphene mesh (3D-PGM) with effective exposure active sites. By a facile controllable process through self-assembly and chemical etching of reduced-graphene oxide, synergetic enhancement of oxygen reduction reaction (ORR) performance from intrinsic activity to apparent activity was realized. The as-obtained materials exhibit 3D interconnected hierarchical porosity for efficient mass transport, a high surface defect content with increased numbers of active sites and a robust conductive network, leading to a comprehensive multiscale electron transfer capability that ultimately enhances the ORR catalytic activity. Incredibly, the alkaline ORR performance of as-obtained catalyst exhibits a 4-electron pathway reaction with an onset potential (Eonset) of 0.89 V, half-wave potential (E1/2) of 0.84 V, and a lower Tafel slope of 58 mV dec−1, showing activity comparable to that of Pt/C catalysts. Moreover, the as assembled primary Zn–air batteries (ZABs) demonstrate a higher power density (182.6 mW cm−2) and a higher specific capacity (809.1 mA h g−1) than the Pt/C-based counterpart. The outstanding electrochemical performance and facile fabrication techniques make this material a promising alternative to commercial Pt/C for renewable energy devices.

DOI： 10.1016/j.carbon.2021.08.066

Structure and properties of nanocarbons-encapsulated WC synthesized by solution plasma process in palm oils

Islam, MZ; Watthanaphanit, A; Chae, S; Niitsu, K; Saito, N

MATERIALS EXPRESS Vol. 11 ( 9 ) page： 1602 - 1607 2021.9

High electrical conductivity and oxidation reduction reaction activity of tungsten carbide/carbon nanocomposite synthesized from palm oil by solution plasma process

Islam, MZ; Watthanaphanit, A; Chae, S; Niitsu, K; Saito, N

MATERIALS EXPRESS Vol. 11 ( 9 ) page： 1587 - 1593 2021.9

Facile synthesis of ZnO nanobullets by solution plasma without chemical additives

Kim K., Chae S., Choi P.G., Itoh T., Saito N., Masuda Y.

RSC Advances Vol. 11 ( 43 ) page： 26785 - 26790 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

ZnO nano-bullets were synthesized using solution plasma from only Zn electrode in water without any chemical agents. In this sustainable synthesis system, the rapid quenching reaction at the interface between the plasma/liquid phases facilitates the fast formation of nano-sized materials. The coil-to-pin type electrode geometry, which overcomes the discharge interruption owing to the electrode gap broadening of the typical pin-to-pin type enables the synthesis of numerous nanomaterials through a stable discharge for 1 h. The as-prepared samples exhibited a high crystalline ZnO structure without post calcination, and the length and width were 71.8 and 29.1 nm, respectively. The main exposed facet of ZnO nano-bullets was the (100) crystal facet, but interestingly, the (101) facet was confirmed at the inclined surfaces in the edges. The (101) crystal facet has an asymmetric Zn and O atom arrangement, and it could result in a focused electron density area with relatively high reactivity. Therefore, ZnO nano-bullets are promising materials for applications in advanced technologies.

DOI： 10.1039/d1ra05008g

Reduced Red Mud as the Solar Absorber for Solar-Driven Water Evaporation and Vapor-Electricity Generation

Wang P., Wang X., Chen S., Zhang J., Mu X., Chen Y., Sun Z., Wei A., Tian Y., Zhou J., Liang X., Miao L., Saito N.

ACS Applied Materials and Interfaces Vol. 13 ( 26 ) page： 30556 - 30564 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

The emergent solar-driven water evaporation technology provides a reassuring scheme for red mud (RM) utilization in environment and materials science. With fewer restrictions on raw materials, wide availability of sheer quantity, and high complexity in chemical composition, the RM may be a promising candidate for solar absorbers. Here, we developed a novel solar absorber with reduced RM. It features favorable light absorption and photothermal conversion ability using biomass pyrolysis. When added to the polyvinyl alcohol and chitosan gel substrate, the light absorptance can reach 94.65%, while the corresponding evaporation rate is as high as 2.185 kg m-2 h-1 under an illumination density of 1 kW m-2. We further demonstrated its potential as an efficient solar absorber in the solar-driven water evaporation and the thermoelectric device to realize the stable and efficient coproduction of vapor and electricity.

DOI： 10.1021/acsami.1c05228

Cationic nitrogen-doped graphene as a p-type modifier for high-performance PEDOT:PSS hole transporters in organic solar cells

Lin H.S., Kaneko T., Ishikawa S., Jeon I., Chae S., Yana T., Saito N., Matsuo Y.

Japanese Journal of Applied Physics Vol. 60 ( 7 ) 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

This research paper reports the enhanced hole-transporting ability of widely utilized poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) achieved by applying cationic nitrogen-doped graphene (CNG) as a p-type modifier for efficient organic solar cells (OSCs). The power conversion efficiency (PCE) of the CNG-coated PEDOT:PSS-applied OSC reaches 2.76%, which is an increase of 40% compared to that of the pristine PEDOT:PSS-applied OSC (1.96%). The significantly enhanced performance is contributed by the increased hole-transporting ability, and the improved interfacial morphology of PEDOT:PSS, which affords high-quality active layers.

DOI： 10.35848/1347-4065/ac00fc

Facile in Situ Synthesis of Amphiphilic Carbon-Supported Pt: Innovative Catalyst Preparation for Proton Exchange Membrane Fuel Cells

Tipplook M., Panomsuwan G., Muta Y., Saito N.

ACS Applied Energy Materials Vol. 4 ( 6 ) page： 5606 - 5614 2021.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Energy Materials

Carbon materials are widely utilized to support platinum (Pt) catalysts for proton exchange membrane fuel cells (PEMFCs). However, carbon surfaces generally promote hydrophobicity, which limits the transport of active species and lowers the efficiency of PEMFCs. Consequently, functional groups should be introduced on the carbon surface to create transport channels. One promising strategy is to modify the amphiphilic functional group on a carbon surface. In this study, the liquid-phase plasma process was applied to realizing a facile one-step synthesis of amphiphilic functional group-modified carbon-supported platinum (Am@C/Pt) to serve as a catalyst. This novel synthesis strategy provides several advantages over conventional processes, such as reducing the number of steps and minimizing the chemical and energy consumptions. Experimental results revealed that the PEMFCs' efficiency with Am@C/Pt is mainly controlled by the number of hydrophilic and hydrophobic characters on the carbon surface. A single PEMFC demonstrated a maximum current and power density of 2.41 A cm-2 and 1.68 W cm-2, respectively, at 0.7 V, which was significantly higher than those of commercially available carbon-supported Pt catalysts. Furthermore, Am@C/Pt demonstrated superior durability after 5000 test cycles.

DOI： 10.1021/acsaem.1c00406

Insight on solution plasma in aqueous solution and their application in modification of chitin and chitosan

Chokradjaroen C., Niu J., Panomsuwan G., Saito N.

International Journal of Molecular Sciences Vol. 22 ( 9 ) 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Molecular Sciences

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the “solution plasma process”, has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

DOI： 10.3390/ijms22094308

Deposition of carbon–tungsten carbide on coir pulp to improve its compatibility with polylactic acid

Boonyeun N., Rujiravanit R., Saito N.

Cellulose Vol. 28 ( 7 ) page： 4119 - 4136 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Cellulose

To increase hydrophobicity of surfaces of coir pulp, carbon–tungsten carbide (WC) was synthesized and simultaneously deposited on coir pulp by applying in-liquid electrical discharge plasma, so-called solution plasma process (SPP). As a result, water contact angle of carbon-WC deposited coir pulp was 123.4°, whereas that of coir pulp was 82.8°. The carbon-WC deposited coir pulp was then used as a filler in polylactic acid (PLA) to attain composite films of PLA/carbon-WC deposited coir pulp. The deposition of carbon-WC on coir pulp not only increased hydrophobicity of coir pulp but also improved compatibility between the filler and PLA. Even at the low filler content of 0.75 wt%, tensile strength and Young’s modulus of composite films of PLA/carbon-WC deposited coir pulp increased up to 45.73% and 22.79%, respectively compared with those of neat PLA film. Furthermore, the presence of carbon-WC deposited coir pulp in the PLA composite films could enhance the formation of crystalline structure of PLA. Accordingly, SPP is an interesting tool for surface modification of coir pulp in order to achieve surface-functionalized coir pulp for using as a filler in green composites. Graphic abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s10570-021-03799-6

Li-air battery and ORR activity of nanocarbons produced with good synthesis rate by solution plasma process Reviewed

Islam M.Z., Watthanaphanit A., Chae S., Saito N.

Materials Advances Vol. 2 ( 8 ) page： 2636 - 2641 2021.4

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Advances

Nanocarbons were successfully synthesized from benzene (BZ), nitro-benzene (BZ-NO2) and aniline (BZ-NH2) by solution plasma process (SPP). The SPP was generated by a bipolar pulsed power supply between two tungsten electrodes at room temperature. The synthesized nanocarbons were investigated. The highest synthesis rate, 40 mg min-1, was for the BZ nanocarbon. The transmission electron microscopy (TEM) morphology showed that the nanocarbon sizes were 15-25 nm. The Brunauer-Emmett-Teller (BET) analysis shows a highest surface area of 220 m2 g-1, pore size of 0.45 cm3 g-1, and average pore diameter of 20.0 nm for the BZ nanocarbon. Cyclic voltammetry (CV) in an acidic medium exhibited the oxygen reduction reaction (ORR) of the nanocarbons. The nanocarbon from BZ-NH2 obtained a high special capacity of 15 500 mA h per g of carbon at the discharge rate of 0.1 mA cm-2 with 1.0 mg carbon loading for the lithium (Li)-air battery. The ORR is an important reaction in Li-air batteries and fuel cells for the application of next-generation batteries and energy conversion devices.

DOI： 10.1039/d0ma00926a

Plasma-assisted synthesis of multicomponent nanoparticles containing carbon, tungsten carbide and silver as multifunctional filler for polylactic acid composite films

Boonyeun N., Rujiravanit R., Saito N.

Polymers Vol. 13 ( 7 ) 2021.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymers

Multicomponent nanoparticles containing carbon, tungsten carbide and silver (carbon-WC-Ag nanoparticles) were simply synthesized via in-liquid electrical discharge plasma, the so-called solution plasma process, by using tungsten electrodes immersed in palm oil containing droplets of AgNO3 solution as carbon and silver precursors, respectively. The atomic ratio of carbon:W:Ag in carbon-WC-Ag nanoparticles was 20:1:3. FE-SEM images revealed that the synthesized carbon-WC-Ag nanoparticles with particle sizes in the range of 20–400 nm had a spherical shape with a bumpy surface. TEM images of carbon-WC-Ag nanoparticles showed that tungsten carbide nanoparticles (WCNPs) and silver nanoparticles (AgNPs) with average particle sizes of 3.46 nm and 72.74 nm, respectively, were dispersed in amorphous carbon. The carbon-WC-Ag nanoparticles were used as multifunctional fillers for the preparation of polylactic acid (PLA) composite films, i.e., PLA/carbon-WC-Ag, by solution casting. Interestingly, the coexistence of WCNPs and AgNPs in carbon-WC-Ag nanoparticles provided a benefit for the co-nucleation ability of WCNPs and AgNPs, resulting in enhanced crystallization of PLA, as evidenced by the reduction in the cold crystallization temperature of PLA. At the low content of 1.23 wt% carbon-WC-Ag nanoparticles, the Young’s modulus and tensile strength of PLA/carbon-WC-Ag composite films were increased to 25.12% and 46.08%, respectively. Moreover, the PLA/carbon-WC-Ag composite films possessed antibacterial activities.

DOI： 10.3390/polym13070991

N-Doped few-layer graphene encapsulated Pt-based bimetallic nanoparticles: Via solution plasma as an efficient oxygen catalyst for the oxygen reduction reaction

Phan P.Q., Naraprawatphong R., Pornaroontham P., Park J., Chokradjaroen C., Saito N.

Materials Advances Vol. 2 ( 1 ) page： 322 - 335 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Advances

N-Doped few-layer graphene encapsulated Pt-based bimetallic nanoparticles were successfully synthesized via the solution plasma (SP) method. This synthesis strategy can be achieved in one pot by using only pure dimethylformamide (DMF) as the reaction solution at room temperature and atmospheric pressure. The structural analyses exhibited a fine core-shell structured nanoparticle (2-4 nm), which had Pt and Pt-based bimetallic nanoparticles as a core and N-doped few-layer graphene (NFG), having 2-4 layers, as a shell. Pt-based bimetallic cores (i.e., PtAu, PtAg, and PtPd) were varied depending on the metal electrodes used in the SP process. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of the obtained samples in an acidic solution was found to be acceptable, while possessing excellent durability, compared to those of the commercial carbon-supported Pt catalyst. The effective ORR activity was possibly attributed to the synergistic effect of the Pt-based bimetallic core and N-doped graphene shell which contained high amounts of pyridinic-N and quaternary-N. The results in a single fuel cell test expressed the superiority of our SP-derived sample in the fuel cell performances to commercial Pt/C. This study not only proposed potential alternative ORR catalysts with acceptable electrocatalytic activity and high durability but also provided guidelines for the facile synthesis of carbon-based core-shell nanostructured materials with low chemical use via the SP process. This journal is

DOI： 10.1039/d0ma00718h

Natural Self-Confined Structure Effectively Suppressing Volume Expansion toward Advanced Lithium Storage Reviewed International coauthorship

Zhang Y., Huang J., Liao Z., Hu A., Li X., Saito N., Zhang Z., Yang L., Hirano S.I.

ACS Applied Materials and Interfaces 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Volume expansion hinders conversion-type transition-metal oxides (TMOs) as potential anode candidates for high-capacity lithium-ion batteries. While nanostructuring and nanosizing have been employed to improve the cycling stability of TMOs, we show here that both high initial Coulombic efficiency (ICE) and stable cycling reversibility are achieved in the layered compound Li0.9Nb0.9Mo1.1O6 (L0.9NMO) by inherent properties of the bulk crystal structure. In this model, MoO6 octahedra as active centers react with lithium ions and endow capacity, while a grid composed of NbO6 octahedra effectively suppresses the volume expansion, enhances the conductivity, and supports the structural skeleton from collapse. As a result, bulk L0.9NMO not only delivers a high discharge capacity of 1128 mA h g-1 at 100 mA g-1 with a considerable ICE of 87% but also exhibits long cycling stability and good rate performance (339 mA h g-1 after 500 cycles at 1 A g-1 with an average Coulombic efficiency approaching 100%). The self-confined structure provides a competitive strategy for stable conversion-type lithium storage.

DOI： 10.1021/acsami.1c02269

Safe, superionic conductive and flexible “polymer-in-plastic salts” electrolytes for dendrite-free lithium metal batteries

Liao Z., Huang J., Chen W., Saito N., Zhang Z., Yang L., Hirano S.i.

Energy Storage Materials Vol. 33 page： 442 - 451 2020.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Energy Storage Materials

Solid polymer electrolytes (SPEs) garner tremendous attention for both enabling higher energy density battery chemistry and alleviating the safety concerns of liquid electrolytes, but the practical utilizations of SPEs are severely hindered by the limited room temperature ionic conductivity, low transference number and huge interface impedance. Unlike the polymer chain movement in traditional SPEs, in the present work, we develop novel “polymer-in-plastic salts” electrolytes (PIPSEs) via a high weight ratio of plastic salts to polymer in which polymer just function as framework so that non-flammable, superionic conductive and flexible SPEs can be obtained. Also, the high content of plastic salts in PIPSEs can wet electrodes and form compatible solid electrolyte interface (SEI) with lithium metal. As a consequence, solid-state dendrite-free symmetric Li cells with PIPSEs show ultralong cycle life over 1000 h under up to 2.0 mA cm−2 and Li/LiFePO4 and high-voltage Li/LiNi0.6Co0.2Mn0.2O2 cells utilizing above PIPSEs exhibit excellent cycle performance and appealing rate performance. It is anticipated that our work provides a new strategy for the next-generation solid-state batteries.

DOI： 10.1016/j.ensm.2020.09.003

Single-walled carbon nanotubes wrapped by cationic nitrogen-doped carbon for electrocatalytic applications Reviewed International coauthorship

Chae S., Phan P.Q., Panomsuwan G., Bratescu M.A., Hashimoto T., Teshima K., Saito N.

ACS Applied Nano Materials Vol. 3 ( 10 ) page： 10183 - 10189 2020.10

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

The exploration of novel carbon material systems has emerged as a promising strategy for yielding unique and unconventional functional properties. In this study, a cationic nitrogen-doped carbonwrapped single-walled carbon nanotube (CN-C@SWCNT) was synthesized for the first time via solution plasma (SP) by using an aniline aqueous solution with the SWCNT dispersion under ambient conditions. The reactive species produced from SP led to the formation of cationic nitrogendoped carbon (CN-C) completely wrapped around SWCNT. Raman spectroscopy, electron diffraction, and X-ray photoelectron spectroscopy confirmed the presence of cationic nitrogen. CN-C@SWCNT exhibited an excellent electrical conductivity of 120.30 S cm-1. Room-temperature halleffect measurements revealed p-type semiconducting behavior for CN-C@ SWCNT, with a carrier concentration of 4.6 × 1020 cm-3. The electrical conductivity and carrier concentration of p-type CN-C@SWCNT were greater than those reported previously for carbon-based materials. The high electrical properties of CN-C@SWCNT were synergistically related to a conducting bridge between CN-C and SWCNT conducting domains and the presence of doped cationic nitrogen. The SP-synthesized CN-C@SWCNT demonstrates immense potential as an emerging class of p-type carbon materials in advanced electrocatalytic applications.

DOI： 10.1021/acsanm.0c02164

In situ synthesis of copper nanoparticles encapsulated by nitrogen-doped graphene at room temperature via solution plasma

Phan P.Q., Chae S., Pornaroontham P., Muta Y., Kim K., Wang X., Saito N.

RSC Advances Vol. 10 ( 60 ) page： 36627 - 36635 2020.10

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Metal-carbon core-shell nanostructures have gained research interest due to their better performances in not only stability but also other properties, such as catalytic, optical, and electrical properties. However, they are limited by complicated synthesis approaches. Therefore, the development of a simple method for the synthesis of metal-carbon core-shell nanostructures is of great significance. In this work, a novel Cu-core encapsulated by a N-doped few-layer graphene shell was successfully synthesized in a one-pot in-liquid plasma discharge, so-called solution plasma (SP), to our knowledge for the first time. The synthesis was conducted at room temperature and atmospheric pressure by using a pair of copper electrodes submerged in a DMF solution as the precursor. The core-shell structure of the obtained products was confirmed by HR-TEM, while further insight information was explained from the results of XRD, Raman, and XPS measurements. The obtained Cu-core encapsulated by the N-doped few-layer graphene shell demonstrated relatively high stability in acid media, compared to the commercial bare Cu particles. Moreover, the stability was found to depend on the thickness of the N-doped few-layer graphene shell which can be tuned by adjusting the SP operating conditions. This journal is

DOI： 10.1039/d0ra07162e

Solution plasma: new synthesis method of N-doped carbon dots as ultra-sensitive fluorescence detector for 2,4,6-trinitrophenol Reviewed International coauthorship

Kim K., Chokradjaroen C., Saito N.

Nano Express Vol. 1 ( 2 ) 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Nano Express

Herein, we report the synthesis of nitrogen-doped carbon dots (NCDs) through solution plasma (SP) for the first time. The SP method occurs a rapid dissociation of molecules, such as organic compounds, caused by an electrical discharge between electrodes immersed in a solution. The dissociation can result in the creation of various radicals such as ·C2, ·CN, and ·H which enable the rapid synthesis of carbon dots (CDs). The unique reaction of radicals allowed the formation of CDs with high N concentration and functionalization of the surface in a short time. In this study, by using the SP method, a very fine NCDs with size of 6 nm were synthesized from a pyridine/water mixture in just 10 min. Bright blue fluorescence (410 nm) with a high quantum yield (61%) was observed due to the high N concentration and the surface passivation. From the potential application point of view, the synthesized NCDs showed an excellent detection property for 2,4,6-trinitrophenol (TNP) by fluorescence quenching effect. It was due to rich amino-functional groups which act as a reaction pathway to TNP. This phenomenon was caused by the synergetic effect of a photo-induced electron transfer with the assistance of proton transfer-assisted electron transfer.

DOI： 10.1088/2632-959X/abb9fa

Effect of electrical discharge plasma on cytotoxicity against cancer cells of N,O-carboxymethyl chitosan-stabilized gold nanoparticles

Chokradjaroen C., Rujiravanit R., Theeramunkong S., Saito N.

Carbohydrate Polymers Vol. 237 2020.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Electrical discharge plasma in a liquid phase can generate reactive species, e.g. hydroxyl radical, leading to rapid reactions including degradation of biopolymers. In this study, the effect of plasma treatment time on physical properties and cytotoxicity against cancer cells of N,O-carboxymethyl chitosan-stabilized gold nanoparticles (CMC-AuNPs) was investigated. AuNPs were synthesized by chemical reduction of HAuCl4 in 2 % CMC solution to obtain CMC-AuNPs, before being subjected to the plasma treatment. Results showed that the plasma treatment not only led to the reduction of hydrodynamic diameters of CMC-AuNPs from 400 nm to less than 100 nm by the plasma-induced degradation of CMC but also provided the narrow size distribution of AuNPs having diameters in the range of 2–50 nm, that were existing in CMC-AuNPs. In addition, the plasma-treated CMC-AuNPs could significantly reduce the percentage of cell viability of breast cancer cells by approximately 80 % compared to the original CMC and CMC-AuNPs.

DOI： 10.1016/j.carbpol.2020.116162

Fabrication of biocomposite membrane with microcrystalline cellulose (MCC) extracted from sugarcane bagasse by phase inversion method

Thiangtham S., Runt J., Saito N., Manuspiya H.

Cellulose Vol. 27 ( 3 ) page： 1367 - 1384 2020.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Cellulose

Abstract: The design of biocomposite membranes based on microcrystalline cellulose (MCC) extracted from sugarcane bagasse added into matrices of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) was fabricated by the phase inversion method. The pore formation of biocomposite membranes was prepared by the phase inversion method, and the obtained biocomposite membranes showed a tunable microstructure formed in the membranes that was investigated by field-emission scanning electron microscope. Due to the high porosity and hydrophilic properties of MCC, the biocomposite membranes demonstrated excellent electrolyte wettability, large electrolyte uptake (up to 138%), and smaller interfacial resistance leading to enhancement of the ionic conductivity. Furthermore, the effects of MCC on the thermal properties of biocomposite membranes were evaluated by differential scanning calorimetry and the thermal shrinkage test. The addition of 5 wt% MCC showed the outstanding thermal stability of the biocomposite membranes. After thermal treatment at 135 °C for 1 h, this biocomposite membrane exhibited shrinkage of only 32% from the original shape while the PLA/PBS membrane showed shrinkage of 81%, which verifies that the introduction of MCC improves the thermal stabilities of biocomposite membranes. Promisingly, the biocomposite membranes represent candidate alternatives for future battery applications. Graphic abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s10570-019-02866-3

Liquid-Phase Plasma-Assisted in Situ Synthesis of Amino-Rich Nanocarbon for Transition Metal Ion Adsorption

Tipplook M., Pornaroontham P., Watthanaphanit A., Saito N.

ACS Applied Nano Materials Vol. 3 ( 1 ) page： 218 - 228 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

Amino-modified nanocarbon (NH2-C) has been widely used as an adsorbent for transition metal ion adsorption due to its high specific surface area, high electrical charge, and the ability to form a coordinate linkage to a transition metal ion. In this work, NH2-C was successfully synthesized from a mixture of phenol and (3-aminopropyl)triethoxysilane (APTES) through solution plasma processing, which performs both carbonization and amination simultaneously. This synthesis method eliminates the need to functionalize carbon with amino groups, as is required in the conventional process. Our NH2-C shows a better dispersion and a higher number of amino groups on both the external surface and inner pores, which enhances the adsorption capacity. The maximum capacities for Cu2+, Zn2+, and Cd2+ adsorption were 144.9, 115.4, and 102.0 mg g-1, respectively. These values were higher than those of five typical NH2-Cs synthesized by a conventional process. Based on the adsorption mechanism derived from adsorption kinetic, isotherm, and thermodynamic studies, the transition metal ions were chemisorbed to the surface in a monolayer endothermically and spontaneously. Moreover, it was found that NH2-C was suitable for use in ten consecutive adsorption-desorption cycles without significant loss of adsorption capacity.

DOI： 10.1021/acsanm.9b01915

Simultaneous deacetylation and degradation of chitin hydrogel by electrical discharge plasma using low sodium hydroxide concentrations

Rujiravanit R., Kantakanun M., Chokradjaroen C., Vanichvattanadecha C., Saito N.

Carbohydrate Polymers Vol. 228 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Electrical discharge plasma occurring in a liquid phase, so called solution plasma, can generate highly active species, e.g. free radicals, which can involve in various chemical reactions, leading to less chemical uses. In this study, solution plasma was applied to deacetylation of chitin aiming to reduce the use of alkali. It was found that solution plasma could induce deacetylation of chitin hydrogels that were dispersed in MeOH/water solutions containing low NaOH concentrations (1–12%). Due to the action of free radicals, some extent of chain session of the polymer occurred during the plasma treatment. The degree of deacetylation and molecular weight of the obtained chitosan were 78% and 220 kDa, respectively, after the plasma treatment for five cycles (1 h/cycle) by using 90% MeOH/water solution containing 12% NaOH. The obtained chitosan could completely dissolve in 2% acetic acid solution and had antibacterial activities against S. aureus and E. coli.

DOI： 10.1016/j.carbpol.2019.115377

Synthesis of Au Nanoparticles in Natural Matrices by Liquid-Phase Plasma: Effects on Cytotoxic Activity against Normal and Cancer Cell Lines Reviewed International coauthorship

Treesukkasem N., Chokradjaroen C., Theeramunkong S., Saito N., Watthanaphanit A.

ACS Applied Nano Materials Vol. 2 ( 12 ) page： 8051 - 8062 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

Wrapping of gold nanoparticles (AuNPs) with a biocompatible matrix, to gain AuNP colloids, is a general strategy to synthesize the AuNPs for biomedical purposes. This work reports the synthesis of AuNP colloids in the aqueous solution of several natural matrices using a liquid-phase plasma process. Two classes of natural substances used are sugars (including: glucose, fructose, and sucrose) and biopolymers (including: carboxymethyl cellulose, sodium alginate, and gelatin). All are negatively charged water-soluble substances that are claimed to be sources of energy for cells to grow and have a high potential to be compatible with them. The study has emerged since one question arises: "Do these matrices also promote the growth of cancer cells?" The synthesis is performed by generating plasma across a pair of electrodes immersed in an aqueous solution of a natural matrix containing a gold precursor (HAuCl4·3H2O). Two concentrations of the matrices (0.5 and 1.0% w/v) are used, and the plasma treatment times are varied (0, 10, and 30 min). The effect of the type and concentration of natural matrices as well as the plasma treatment time on the formation of AuNPs, along with their physical and chemical properties, including morphology, size, hydrodynamic diameter (dh), colloidal stability, and charge on the AuNP surface, is evaluated. We find that the charge of the AuNP surfaces could be altered by the plasma treatment. Eventually, cytotoxicity test results against normal (MRC-5) and cancer (H460 and HeLa) cell lines could not only answer our opening question but also suggest a rather complex response. Our findings indicate the great potential of the obtained AuNP colloids as a part of cancer therapy.

DOI： 10.1021/acsanm.9b02106

Nitriding an oxygen-doped nanocarbonaceous sorbent synthesized via solution plasma process for improving CO<inf>2</inf> adsorption capacity

Pornaroontham P., Panomsuwan G., Chae S., Saito N., Thouchprasitchai N., Phongboonchoo Y., Pongstabodee S.

Nanomaterials Vol. 9 ( 12 ) 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanomaterials

The synthesis of carbon nanoparticles (Cn) and oxygen-doped nanocarbon (OCn) was successfully done through a one-step synthesis by the solution plasma process (SPP). The Cn and OCn were nitrogen-doped by nitridation under an ammonia atmosphere at 800◦C for 2 h to yield NCn and NOCn, respectively, for carbon dioxide (CO2) adsorption. The NOCn exhibited the highest specific surface area (~570 m2 g−1) and highest CO2 adsorption capacity (1.63 mmol g−1 at 25◦C) among the synthesized samples. The primary nitrogen species on the surface of NOCn were pyridinic-N and pyrrolic-N. The synergistic effect of microporosity and nitrogen functionality on the NOCn surface played an essential role in CO2 adsorption enhancement. From the thermodynamic viewpoint, the CO2 adsorption on NOCn was physisorption, exothermic, and spontaneous. The NOCn showed a more negative enthalpy of adsorption, indicating its stronger interaction for CO2 on the surface, and hence, the higher adsorption capacity. The CO2 adsorption on NOCn over the whole pressure range at 25–55◦C best fitted the Toth model, suggesting monolayer adsorption on the heterogeneous surface. In addition, NOCn expressed a higher selective CO2 adsorption than Cn and so was a good candidate for multicycle adsorption.

DOI： 10.3390/nano9121776

Quantitative spectrochemical analysis of solution plasma in aromatic molecules

Bratescu M.A., Kim K., Saito N.

Plasma Processes and Polymers Vol. 16 ( 7 ) 2019.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Processes and Polymers

A nonthermal plasma produced at atmospheric pressure in the gas resulted from the surrounding liquid is named solution plasma (SP). A quantitative and comparative spectrochemical analysis of the plasma gas and solution in benzene, pyridine, and aniline is performed. The number densities of dicarbon and cyano radicals and hydrogen molecule from the plasma gas are measured using a cheap, straightforward, and home-made optical set-up. By simply modifying the optical set-up, the molar concentration of newly formed chemical compounds is in situ obtained in the solution. The thermodynamic properties of aromatic molecules determine the electrical breakdown and the species number densities in the plasma gas. The production rate and atomic composition of carbon material are correlated with the radicals from plasma gas.

DOI： 10.1002/ppap.201900012

P-Type Doping of Graphene with Cationic Nitrogen

Chae S., Panomsuwan G., Bratescu M.A., Teshima K., Saito N.

ACS Applied Nano Materials Vol. 2 ( 3 ) page： 1350 - 1355 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

Tailoring electrical properties of graphene by nitrogen doping is currently of great significance in a broad area of advanced applications. Bonding configuration of nitrogen atoms in graphene plays a vital role in controlling its electrical, chemical, and optical properties. Here, we report for the first time a simple bottom-up synthesis of a novel cationic nitrogen-doped graphene (CNG) by a solution plasma (SP). A mixture of ionic liquid and organic solvent was used as starting precursor. CNG exhibited an orthorhombic structure possibly due to the presence cationic nitrogen in hexagonal graphene lattice. Nitrogen doping content was found to be as high as 13.4 atom %. Electrical characterization demonstrated that the CNG exhibited a p-type semiconducting behavior with superior electrical conductivity and carrier concentration. Such unique electrical characteristics of CNG are mainly attributed to the presence of cationic nitrogen with preserved planar structure.

DOI： 10.1021/acsanm.8b02237

Production of reducing sugar from cassava starch waste (CSW) using solution plasma process (SPP)

Prasertsung I., Aroonraj K., Kamwilaisak K., Saito N., Damrongsakkul S.

Carbohydrate Polymers Vol. 205 page： 472 - 479 2019.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

The cassava starch processing plays an important role in food industries. During starch processing stage, a large amount of cassava starch waste (CSW) which mainly contains lost starch product and solid residue such as cassava bagasse are produced. Starch and cassava bagasse can be hydrolyzed into fermentable sugar such as glucose. In the present study, the solution plasma process (SPP) is used to treat CSW to prepare reducing sugar. The investigated parameters are treatment time, solvent concentration, applied pulsed frequency, and CSW concentration. The %yield of total reducing sugar (TRS) and glucose were calculated by DNS method and glucose assay kit, respectively. The chemical structure, morphology, and crystal structure of plasma-treated CSW were investigated. The results showed that the %yield of TRS was greatly enhanced by SPP treatment compared to that of acid hydrolysis. The CSW powder completely broke down into pieces after SPP treatment was applied. The amorphous and crystalline regions of CSW were destroyed during SPP treatment. SPP treatment of CSW with light sulfuric acid concentration of 0.08 M, applied pulsed frequency of 30 kHz, and CSW concentration of 0.5%w/v provided 99.0% TRS and 47.9% glucose.

DOI： 10.1016/j.carbpol.2018.10.090

Enhanced degradation of methylene blue by a solution plasma process catalyzed by incidentally co-generated copper nanoparticles

Prasertsung I., Kaewcharoen S., Kunpinit K., Yaowarat W., Saito N., Phenrat T.

Water Science and Technology Vol. 79 ( 5 ) page： 967 - 974 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Water Science and Technology

This study presents a catalytic organic pollution treatment using the solution plasma process (SPP) with incidentally co-generated copper (Cu) nanoparticles via Cu electrode erosion. Methylene blue (MB) was used as a model organic contaminant. The treatment time was from 0 to 60 minutes at the plasma frequencies of 15 and 30 kHz. The treatment efficacy using the Cu electrode was compared with that of the tungsten (W) electrode. The high erosion-resistant W electrode provided no W nanoparticles, while the low erosion-resistant Cu electrode yielded incidental nanoparticles (10-20 nm), hypothesized to catalyze the MB degradation during the SPP. The percentage of MB degradation and the hydrogen peroxide (H2O2) generation were determined by an ultraviolet-visible spectrophotometer. The results showed that, after the SPP by the Cu electrode for 60 minutes, the MB was degraded up to 96%. Using the Cu electrode at a high plasma frequency strongly accelerated the Cu nanoparticle generation and MB treatment, although the amount of H2O2 generated during the SPP using the Cu electrode was less than that of the W electrode. The Cu nanoparticles were hypothesized to enhance MB degradation via both homogeneous (release of dissolved Cu ions) and heterogeneous (on the surface of the particles) catalytic processes.

DOI： 10.2166/wst.2019.035

Maximization of sodium storage capacity of pure carbon material used in sodium-ion batteries Reviewed International coauthorship

Kang J., Kim D.Y., Chae S.A., Saito N., Choi S.Y., Kim K.H.

Journal of Materials Chemistry A Vol. 7 ( 27 ) page： 16149 - 16160 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A

Generally, carbon anode materials used in sodium-ion batteries do not exhibit good electrochemical performance because of low coulombic efficiency (CE). This paper presents a strategy to overcome this limitation by causing a co-intercalation reaction in a newly designed material. Here, Na was doped inside carbons and desodiation was caused by cleaning the doped Na. Consequently, the CE consistently exceeded 100%. Furthermore, new spaces were created when the doped Na was released continuously from the carbons, thereby allowing more Na to be stored in these spaces. This consistently increased the reversible capacity during cycling. Even though the designed material was a nanomaterial with a large specific surface area, the CE in the first cycle was 85%. Because of the co-intercalation reaction, a solid-electrolyte interphase (SEI) layer might not be formed depending on the anode surface structure and continuous long-term stable cycling was possible even without an SEI layer. Thus, a useful material for sodium-ion batteries can be designed using only carbons and without next-generation materials.

DOI： 10.1039/c9ta01751h

Solution plasma-assisted green synthesis of MnO <inf>2</inf> adsorbent and removal of cationic pollutant

Kim H., Saito N., Kim D.

Journal of Chemistry Vol. 2019 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemistry

In this study, we proposed the solution plasma-(SP-) assisted green synthesis method using plants extracts, i.e., glucose, with the expectation of acting as a reducing agent and promotor for the formation of powder state of nanostructured MnO 2 . MnO 2 was simply and rapidly synthesized within 10 min by the SP-assisted method. The structural features and morphology of as-synthesized MnO 2 were characterized by XRD, Raman, FE-SEM, and TEM analyses. For potential application of as-synthesized MnO 2 , cationic dye, i.e., methylene blue (MB), removal performance was investigated by batch experiment at an initial concentration of C 0 = 100 mg L -1 . The obtained MnO 2 exhibited effective dye removal ability given high C 0 , and simultaneously applied plasma discharging further enhanced removal efficiency. These contributions therefore open a new window not only on a powerful and environmentally benign synthesis route for efficient adsorbents but also on supporting multiple removal mechanism.

DOI： 10.1155/2019/7494292

Cytotoxicity against cancer cells of chitosan oligosaccharides prepared from chitosan powder degraded by electrical discharge plasma

Chokradjaroen C., Theeramunkong S., Yui H., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 201 page： 20 - 30 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Chitosan oligosaccharides, which obtain from degradation of chitosan, possess some interesting molecular weight-dependent biological properties, especially anticancer activity. Therefore, the conversion of chitosan to chitosan oligosaccharides with specific molecular weight has been continuously investigated in order to find effective strategies that can achieve both economic feasibility and environmental concerns. In this study, a novel process was developed to heterogeneously degrade chitosan powder by highly active species generated by electrical discharge plasma in a dilute salt solution (0.02 M) without the addition of other chemicals. The degradation rate obtained from the proposed process was comparable to that obtained from some other methods with the addition of acids and oxidizing agents. Separation of the water-soluble degraded products containing chitosan oligosaccharides from the reaction solution was simply done by filtration. The obtained chitosan oligosaccharides were further evaluated for an influence of their molecular weights on cytotoxicity against cancer cells and the selectivity toward cancer and normal cells.

DOI： 10.1016/j.carbpol.2018.08.037

Mechanistic aspect based on the role of reactive oxidizing species (ROS) in macroscopic level on the glycerol photooxidation over defected and defected-free TiO<inf>2</inf>

Jedsukontorn T., Ueno T., Saito N., Hunsom M.

Journal of Photochemistry and Photobiology A: Chemistry Vol. 367 page： 270 - 281 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Photochemistry and Photobiology A: Chemistry

The activity of commercial (defected-free) TiO2 and black (defected) TiO2 photocatalysts was comparatively tested in the glycerol photooxidation reaction. The preliminary results demonstrated that similar compounds, including glyceraldehyde (GCD), dihydroxyacetone (DHA), glycolic acid (GCOA), formaldehyde (FMD) and glycolaldehyde (GCAD), were generated from the photocatalytic oxidation of glycerol via both photocatalysts, but they differed in their yields. The black TiO2 exhibited a higher photocatalytic activity to convert glycerol than the commercial TiO2, due to the presence of some defective structure and its low band gap energy, and also promoted the generation of GCAD as the main product. In contrast, the commercial TiO2 promoted the formation of GCD as the major product. The principle reactive oxidizing species (ROS) contributing for glycerol conversion via black TiO2 can be ranked in the order of O2•->O12>OHb•>h+/OHs•>h+. The dominate ROS related to the conversion of glycerol to GCD and DHA were O2•- and OHb•, respectively. The main ROS to alter GCD and DHA to GCAD/FMD was O2•-, while the h+ was the principle ROS to convert GCD to GCOA. Finally, the pathway of glycerol conversion and product distribution over black TiO2 via various ROS in the presence of oxygen as electron acceptor is proposed.

DOI： 10.1016/j.jphotochem.2018.08.030

One-pot synthesis of purple benzene-derived MnO<inf>2</inf>-carbon hybrids and synergistic enhancement for the removal of cationic dyes Reviewed

Kim H., Saito N.

Scientific Reports Vol. 8 ( 1 ) 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

MnO2-carbon hybrid (MnO2-C-PBz) was simultaneously synthesized by a one-step solution plasma process (SPP) using a single precursor referred to as "purple benzene", which was derived from the K+(dicyclohexano-18-crown-6 ether) complex. To clarify the synergistic effects on the cationic dye removal, MnO2-free carbon and carbon-free MnO2 samples were concurrently investigated. The results of adsorption for cationic dyes (methylene blue (MB) and rhodamine B (Rh B)) and anionic dye (methyl orange (MO)) revealed remarkably high affinity for cationic dyes. In particular, MnO2-C-PBz exhibited the highest adsorption capacity for MB, i.e., ∼3 times greater than that of the others. In addition, MnO2-C-PBz exhibited a rapid, high decolorization ability at C0 = 10 mg L-1 (within a few seconds, ∼99%) and at C0 = 100 mg L-1 (within 30 min, ∼81%), and the theoretical maximum monolayer adsorption capacity was 357.14 mg g-1 as calculated from the Langmuir adsorption isotherm equation. Furthermore, compared with carbon-free MnO2, MnO2-C-PBz exhibited quite a good cyclic stability. We expect that our findings give rise to the understanding of the synergistic effects of MnO2-carbon hybrid, as well as role of each components for the cationic dye adsorption, and may open an innovative synthesis approach to inorganic-organic hybrid materials.

DOI： 10.1038/s41598-018-22203-1

Narrowing band gap energy of defective black TiO<inf>2</inf> fabricated by solution plasma process and its photocatalytic activity on glycerol transformation

Jedsukontorn T., Ueno T., Saito N., Hunsom M.

Journal of Alloys and Compounds Vol. 757 page： 188 - 199 2018.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Defective black titania (TiO2) was synthesized by the solution plasma technique at ambient temperature and pressure. The effects of the electrolyte solution medium type (KCl and HNO3) and concentration (0.3 and 3.0 mM) as well as the plasma discharge time (1–4 h) with a Ti electrode were investigated. The 3.0 mM HNO3 solution provided the highest energy per second discharging into the plasma, resulting in both a high synthesis rate of black TiO2 and a high degree of defective structures, as monitored in terms of the Ti3+/Ti4+ ratio, which can shorten the band gap energy (Eg) of the obtained black TiO2. A long plasma discharge time (4 h) induced the formation of large particles of black TiO2, which appeared as a highly defective structure. Overall, the black TiO2 prepared by discharged plasma for 4 h in 3.0 mM HNO3 solution (BTN-304) provided the highest photocatalytic activity for glycerol conversion (58.49% at 24 h) and 4.85, 3.32, 2.11, 2.15, 39.15 and 26.61% yield of glyceraldehyde, dihydroxyacetone, hydroxypyruvic acid, glycolic acid, glycolaldehyde and formaldehyde, respectively. Pathway of glycerol conversion and product distribution over black TiO2 was attempted to propose. Finally, the reusability of the best black TiO2 was explored.

DOI： 10.1016/j.jallcom.2018.05.046

Thickness-Dependent Strain Evolution of Epitaxial SrTiO<inf>3</inf> Thin Films Grown by Ion Beam Sputter Deposition

Panomsuwan G., Saito N.

Crystal Research and Technology Vol. 53 ( 8 ) 2018.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystal Research and Technology

Epitaxial SrTiO3 (STO) thin films are grown on vicinal (001)-oriented LaAlO3 (LAO) substrates with various thicknesses (3–108 nm) by an ion beam sputter deposition (IBSD). Thickness-dependent strain in the STO films is investigated comprehensively through the X-ray analysis. The STO films grow on the LAO substrates under a compressive strain along in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). With increasing film thickness, the STO unit cells evolve from more to less tetragonal structure, indicating the occurrence of strain relaxation. Quantitative strain analysis is also carried out for all STO films in terms of biaxial and hydrostatic components. It is found that the major cause of strain in STO films is caused by biaxial component over hydrostatic component. The surface morphology of STO films exhibit a step-and-terrace structure with roughness close to the LAO substrate (approx. 0.1 nm), indicating a 2D growth mode. However, as the film thickness increases, the surface terrace become rougher, which is caused by the effect of strain relaxation.

DOI： 10.1002/crat.201700211

Enhancing Bifunctional Catalytic Activity of Oxygen Reduction and Evolution Reaction via One-Pot Formation of MnO<inf>2</inf>-Carbon Hybrid Nanocomposite

Kim H., Saito N., Kim D.

ChemistrySelect Vol. 3 ( 23 ) page： 6302 - 6308 2018.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ChemistrySelect

While manganese dioxide (MnO2) is a promising bifunctional electrocatalyst for oxygen reduction and evolution reaction (ORR/OER) in alkaline media, electrochemical performance of bulk MnO2 limited by their poor electrical conductivity. Herein, we fabricate a MnO2-carbon nanoparticle hybrid composite (MO-CNP) by applying the plasma discharge in the single precursor of purple benzene. This synthesis route facilitates a simultaneous formation of MnO2 and carbon, which induced a homogeneously mixed and firmly anchored hybrid composite. As a result, as-obtained MO-CNP-1 shows more than 12 times higher electrical conductivity than that of prepared conventionally. Thus, formation of MO-CNP could be accompanied by a synergy between MnO2 and CNP as electrocatalyst, and consequently, electrochemical properties were significantly improved. In comparison with CNP, the ORR potential of MO-CNP-1 was positively shifted from –0.28 to –0.23 V (vs. Ag/AgCl), and current density has increased more than 2 times. Although the ORR activity of MO-CNP-1 was still far a little short of the commercial Pt/C, the MO-CNP-1 indicated significant higher OER activity, which demonstrated excellent overall catalytic capability of MO-CNP-1 as bifunctional catalyst.

DOI： 10.1002/slct.201800851

Nano-Assembled Thin Films of Tetraphenylporphyrin on Amine Silane-Modified Substrate for the Optical Gas Sensor

Tipplook, M; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 667 - 674 2018.5

The Nano-Structure and Their Properties of Exfoliation Several Layers-Stacked Graphene Prepared from Graphite Dispersed in Aqueous Solutions by Solution Plasma

Chae, S; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 784 - 789 2018.5

The Initial Reactions from Pyridine to Hetero-Carbon Nanomaterials Through Solution Plasma

Kim, K; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 814 - 819 2018.5

Photoinduced glycerol oxidation over plasmonic au and aum (M = Pt, Pd and Bi) nanoparticle-decorated TiO<inf>2</inf> photocatalysts

Jedsukontorn T., Saito N., Hunsom M.

Nanomaterials Vol. 8 ( 4 ) 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanomaterials

In this study, sol-immobilization was used to prepare gold nanoparticle (Au NP)-decorated titanium dioxide (TiO2) photocatalysts at different Au weight % (wt. %) loading (Aux/TiO2, where x is the Au wt. %) and Au–M NP-decorated TiO2 photocatalysts (Au3M3/TiO2), where M is bismuth (Bi), platinum (Pt) or palladium (Pd) at 3 wt. %. The Aux/TiO2 photocatalysts exhibited a stronger visible light absorption than the parent TiO2 due to the localized surface plasmon resonance effect. Increasing the Au content from 1 wt. % to 7 wt. % led to increased visible light absorption due to the increasing presence of defective structures that were capable of enhancing the photocatalytic activity of the as-prepared catalyst. The addition of Pt and Pd coupled with the Au3/TiO2 to form Au3M3/TiO2 improved the photocatalytic activity of the Au3/TiO2 photocatalyst by maximizing their light-absorption property. The Au3/TiO2, Au3Pt3/TiO2 and Au3Pd3/TiO2 photocatalysts promoted the formation of glyceraldehyde from glycerol as the principle product, while Au3Bi3/TiO2 facilitated glycolaldehyde formation as the major product. Among all the prepared photocatalysts, Au3Pd3/TiO2 exhibited the highest photocatalytic activity with a 98.75% glycerol conversion at 24 h of reaction time.

DOI： 10.3390/nano8040269

Accelerated formation of nanocarbons in solution plasma using benzene substituted with CF<inf>3</inf> group

Panomsuwan G., Li O.L., Saito N., Ishizaki T.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Nanocarbons were synthesized by a solution plasma method using benzene (C6H6) and benzotrifluoride (C5H5CF3) as precursors. The effects of the substituted CF3 group on the overall properties of synthesized nanocarbons were investigated and discussed. As determined from the characterization results, the nanocarbons obtained from both benzene and benzotrifluoride mainly exhibited an amorphous structure and their diameter was about 20-40 nm. There were no notable differences in morphology, surface area, and crystalline structure observed between them. Interestingly, the synthesis rate of nanocarbons from benzotrifluoride (20.3 mg/min) was almost three fold higher than that from benzene (7.6 mg/min). Moreover, a lower H/C ratio was observed in the case of nanocarbons from benzotrifluoride, indicating its more efficient H abstraction. The higher synthesis rate and lower H/C ratio of nanocarbons from benzotrifluoride were possibly attributed to the CF3 radicals generated in the reaction fields of solution plasma during synthesis.

DOI： 10.7567/JJAP.57.0102B6

Degradation of chitosan hydrogel dispersed in dilute carboxylic acids by solution plasma and evaluation of anticancer activity of degraded products

Chokradjaroen C., Rujiravanit R., Theeramunkong S., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Chitosan is a polysaccharide that has been extensively studied in the field of biomedicine, especially its water-soluble degraded products called chitooligosaccharides (COS). In this study, COS were produced by the degradation of chitosan hydrogel dispersed in a dilute solution (i.e., 1.55 mM) of various kinds of carboxylic acids using a non-thermal plasma technology called solution plasma (SP). The degradation rates of chitosan were influenced by the type of carboxylic acids, depending on the interaction between chitosan and each carboxylic acid. After SP treatment, the water-soluble degraded products containing COS could be easily separated from the water-insoluble residue of chitosan hydrogel by centrifugation. The production yields of the COS were mostly higher than 55%. Furthermore, the obtained COS products were evaluated for their inhibitory effect as well as their selectivity against human lung cancer cells (H460) and human lung normal cells (MRC-5).

DOI： 10.7567/JJAP.57.0102B5

In vitro cytotoxicity of carbon black nanoparticles synthesized from solution plasma on human lung fibroblast cells

Panomsuwan G., Chokradjaroen C., Rujiravanit R., Ueno T., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Carbon black nanoparticles (CB-NPs) have been synthesized from liquid benzene by a solution plasma method at room temperature and atmospheric pressure. The morphological observation by scanning electron microscopy revealed the agglomeration of aggregated fine particles. The synthesized CB-NPs were predominantly amorphous as confirmed by X-ray diffraction. The in vitro cytotoxicity of CB-NPs on the human lung fibroblast (MRC-5) cell line was assessed by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and systematically compared with those of two types of commercial carbon blacks (i.e., Vulcan XC-72 and Ketjenblack EC-600JD). Cell viabilities were studied at different concentrations of 32.5, 65, 125, and 250 μg/mL. It was found that the CB-NPs derived from solution plasma exhibited a lower cytotoxicity on the MRC-5 cells than the other two comparative carbon blacks. The viability of MRC-5 cells exposed to CB-NPs remained higher than 90% even at a high concentration of 250 μg/mL. This result preliminarily confirmed the biosafety and potential use of CB-NPs in the field of biological applications.

DOI： 10.7567/JJAP.57.0102BG

Plasma in Solution and Its Applications

Saito N., Nakamura J., Shirafuji T., Ishizaki T.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Solution plasma applications for the synthesis/modification of inorganic nanostructured materials and the treatment of natural polymers

Watthanaphanit A., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Reducing the use of toxic chemicals, production steps, and time consumption are important concerns for researchers and process engineers to contribute in the quest for an efficient process in any production. If an equipment setup is simple, the process additionally becomes more profitable. Combination of the mentioned requirements has opened up various applications of the solution plasma process (SPP) - a physical means of generating plasma through an electrical discharge in a liquid medium at atmospheric pressure and room temperature. This review shows the progress of scientific research on the applications of the SPP for the synthesis/modification of inorganic nanostructured materials and the treatment of natural polymers. Development achieved in each application is demonstrated.

DOI： 10.7567/JJAP.57.0102A3

Solution plasma: A new reaction field for nanomaterials synthesis

Saito N., Bratescu M.A., Hashimi K.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Solution plasma is a new electrical discharge process where an atmospheric non-equilibrium plasma is generated, usually at room temperature, in a liquid environment, such as an aqueous solution or an organic compound. There are a large variety of combinations used in experiments among solutions, electrode materials, plasma configurations, volumes, and reactor geometries, as well as the characteristics of the power supply. The solution plasma process (SPP) combines gas discharge physics, fluid thermodynamic properties, and fluid interfaces reactions. In SPP, nanoparticles with various sizes, shapes, crystallinities, and compositions could be obtained. The synthesis of carbon and hetero-carbon nanomaterials proves that SPP is an efficient and rapid method for their production. The polymerization of benzene in SPP can form graphene. By simply changing the organic precursor, carbon-doped nanostructures can be synthesized with a controlled composition. This review demonstrates that SPP is a new reaction field for nanomaterial production.

DOI： 10.7567/JJAP.57.0102A4

Synthesis of silicon-carbon black composite as anode material for lithium ion battery

Kim H., Yun Y., Lee Y.C., Lee M.H., Saito N., Kang J.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Silicon has been attracting attention as an anode material that can be used for the design of high-capacity lithium ion batteries (LIB). However, the long-term cycling performance of silicon is limited owing to exfoliation from the current collector, resulting from volumetric expansion upon alloying with lithium in the charging process. However, carbon black is an agglomerate of primary particles that form a network and can incorporate a sufficient void space between network structures to accommodate the volumetric expansion of silicon. In this study, we propose the possibility of preventing the volume expansion and exfoliation of silicon by capturing silicon nanoparticles in the void space of the carbon black network. A silicon-carbon black composite material with this structure was successfully synthesized by solution plasma processing.

DOI： 10.7567/JJAP.57.0102B2

Enhancement of nitrogen self-doped nanocarbons electrocatalyst via tune-up solution plasma synthesis

Lee S., Saito N.

RSC Advances Vol. 8 ( 62 ) page： 35503 - 35511 2018

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

The development of a metal-free carbon based electrocatalyst for the oxygen reduction reaction (ORR) is an essential issue for energy conversion systems. Herein, we suggest a tune-up solution plasma (SP) synthesis based on a simple one-step and cost-effective method to fabricate nitrogen self-doped graphitic carbon nanosheets (NGS) as an electrocatalyst. This novel strategy using a low-pass filter circuit provides plasma stability and energy control during discharge in pyridine, determining the graphitic structure of nanocarbons doped with nitrogen. Notably, NGS have a relatively high surface area (621 m2 g−1), and high contents of nitrogen bonded as pyridinic-N and pyrrolic-N of 55.5 and 21.3%, respectively. As an efficient metal-free electrocatalyst, NGS exhibit a high onset potential (−0.18 V vs. Ag/AgCl) and a 3.8 transferred electron pathway for ORR in alkaline solution, as well as better long-term durability (4% current decrease after 10 000 s of operation) than commercial Pt/C (22% current drop). From this point of view, the nitrogen self-doped graphitic carbon nanosheet material synthesized using the tune-up SP system is a promising catalyst for the ORR, as an alternative to a Pt catalyst for application in energy conversion devices.

DOI： 10.1039/C8RA06614K

The solution plasma process for heteroatom-carbon nanosheets: The role of precursors

Hyun K., Saito N.

Scientific Reports Vol. 7 ( 1 ) 2017.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

The solution plasma process (SPP), known as non-equilibrium cold plasma at atmospheric pressure and room temperature, was used to investigate the synthesis of nitrogen-carbon nasnosheets (NCNs). To verify the effect of elementary composition and structure of N-methyl-2-pyrrolidone (NMP), various precursors were used in the SPP to synthesize NCNs via the bottom-up synthesis method for the first time. The NCNs were analyzed by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Among the various precursors, SPP of 2-pyrrolidone was demonstrated to facilitate the formation of highly ordered NCNs. On the other hand, the SPP with cyclopentanone, cyclohexanone and pyrrole did not lead to the formation of carbon nanosheets. The results of this study would uncover new parameter fields for the growth of heteroatom-carbon nanosheets using this synthesis system. In addition, the study is expected to contribute toward research in improving the large-area growth and quality of two-dimensional nanostructures, such as heteroatom-carbon nanosheets or graphene, for various applications in other synthesis methods.

DOI： 10.1038/s41598-017-04190-x

Solution Plasma Process-Derived Defect-Induced Heterophase Anatase/Brookite TiO<inf>2</inf> Nanocrystals for Enhanced Gaseous Photocatalytic Performance

Pitchaimuthu S., Honda K., Suzuki S., Naito A., Suzuki N., Katsumata K.I., Nakata K., Ishida N., Kitamura N., Idemoto Y., Kondo T., Yuasa M., Takai O., Ueno T., Saito N., Fujishima A., Terashima C.

ACS Omega Vol. 3 ( 1 ) page： 898 - 905 2017.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Omega

We report a simple room-temperature synthesis route for increasing the reactivity of a TiO2 photocatalyst using a solution plasma process (SPP). Hydrogen radicals generated from the SPP chamber interact with the TiO2 photocatalyst feedstock, transforming its crystalline phase and introducing oxygen vacancy defects. In this work, we examined a pure anatase TiO2 as a model feedstock because of its photocatalytic attributes and well-characterized properties. After the SPP treatment, the pure anatase crystalline phase was transformed to an anatase/brookite heterocrystalline phase with oxygen vacancies. Furthermore, the SPP treatment promoted the absorption of both UV and visible light by TiO2. As a result, TiO2 treated by the SPP for 3 h showed a high gaseous photocatalytic performance (91.1%) for acetaldehyde degradation to CO2 compared with the activity of untreated TiO2 (51%). The SPP-treated TiO2 was also more active than nitrogen-doped TiO2 driven by visible light (66%). The overall photocatalytic performance was related to the SPP treatment time. The SPP technique could be used to enhance the activity of readily available feedstocks with a short processing time. These results demonstrate the potential of this method for modifying narrow-band gap metal oxides, metal sulfides, and polymer composite-based catalyst materials. The modifications of these materials are not limited to photocatalysts and could be used in a wide range of energy and environment-based applications.

DOI： 10.1021/acsomega.7b01698

Synthesis of Few-Layer Graphene by Peeling Graphite Flakes via Electron Exchange in Solution Plasma

Chae S., Bratescu M., Saito N.

Journal of Physical Chemistry C Vol. 121 ( 42 ) page： 23793 - 23802 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Compared with conventional graphene, few-layer graphene is an easy-to-use material because of its interesting mechanical and chemical properties. Meanwhile, solution plasma (SP) represents a nonequilibrium discharge, which induces electron exchange similar to a catalyst. Thus, SP serves as an electron donor and acceptor between organic molecules and graphite flakes in a solution. Finally, electron exchange leads to the formation of few-layer graphene by peeling graphite flakes. Furthermore, CN-functionalized few-layer graphene (f-FLG) exhibits excellent stability and dispersibility because of the balance of attractive and repulsive forces, i.e., the van der Waals force between the planes and the electrostatic force of the nitrile functional groups on the edges. In this study, f-FLG was successfully synthesized by peeling graphite flakes via electron exchange induced by SP in an aqueous solution containing an ionic liquid (IL) (1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA)). X-ray diffraction measurements revealed that the intensity of the 002 diffraction of graphite and the crystallite size along the [001] direction decreased to about 5 nm after SP treatment, indicating the progress of graphite flake peeling. Furthermore, the purified product comprised three layers with a crystallite size along the basal plane of about 80 nm evaluated by the deconvolution of the Raman 2D band. X-ray photoelectron spectroscopy confirmed that the synthesized f-FLG contains 7.7 atom % nitrogen, and the IR spectrum revealed the presence of the CN functional group. To understand the peeling mechanism, the ionization potential (IP) and electron affinity (EA) of the IL in water, and the averaged electron excitation temperature (Te) in plasma were estimated by ab initio molecular orbital calculations, cyclic voltammetry, and optical emission spectroscopy. An energy diagram of IP, EA, and Te shows that SP served to pump electrons for their circulation via EMIM-DCA and to remove electrons from graphite flakes and inject into f-FLG.

DOI： 10.1021/acs.jpcc.7b08516

Conversion of cellulose into reducing sugar by solution plasma process (SPP)

Prasertsung I., Chutinate P., Watthanaphanit A., Saito N., Damrongsakkul S.

Carbohydrate Polymers Vol. 172 page： 230 - 236 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

In the present study, cellulose colloids are treated with the solution plasma process in order to prepare reducing sugar. The investigated parameters are treatment time, type of electrodes, and applied pulse frequency of the bipolar supply. The reducing sugar was characterized by DNS method and the%yield of total reducing sugar (TRS) was then calculated. The crystal structure and chemical structure of plasma-treated cellulose was measured by XRD and FT-IR, respectively. The%yield of TRS was greatly enhanced by solution plasma treatment using Fe electrode. SEM and TEM micrograph indicated that Fe electrode yield the incidental Fe nanoparticles, hypothesized to catalyze the cellulose degradation during SPP treatment. The crystal structure of cellulose was destroyed. Solution plasma treatment of cellulose using Fe electrode at the high applied frequency pulse provided the highest%TRS.

DOI： 10.1016/j.carbpol.2017.05.025

Generation of non-equilibrium condition in solution plasma discharge using low-pass filter circuit

Heo Y., Lee S., Bratescu M., Kim S., Lee G., Saito N.

Plasma Processes and Polymers Vol. 14 ( 8 ) 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Processes and Polymers

Solution plasma process has been researched as one of the synthetic methods of nano- and functional materials using plasma discharge in liquids. In this study, a low-pass filter circuit was introduced to increase the density and temperature of electrons involved in a non-equilibrium condition. The discharge properties of the solution plasma generated by conventional and low-pass filter circuits were characterized and comparatively analyzed. Filtration of the MHz range current oscillations, an increase in the maximum discharge current, and a higher stability of solution plasma were obtained by simply inserting a resistor-capacitor (RC) component in the circuit, which leads to the increases in the density and temperature of electrons.

DOI： 10.1002/ppap.201600163

Simple Solution Plasma Synthesis of Hierarchical Nanoporous MnO<inf>2</inf> for Organic Dye Removal

Kim H., Watthanaphanit A., Saito N.

ACS Sustainable Chemistry and Engineering Vol. 5 ( 7 ) page： 5842 - 5851 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Sustainable Chemistry and Engineering

We have demonstrated a simple and green approach to synthesize hierarchical nanoporous MnO2 by applying plasma in a liquid precursor; the approach is named the "solution plasma process (SPP)." Three types of sugar, i.e., glucose, fructose, and sucrose, were used as inducers for the nanoporous MnO2 formation (hereafter called G-MnO2, F-MnO2, and S-MnO2). These were successfully synthesized within a few minutes (7-19 min) under ambient conditions. It was confirmed that the generated numerous reactive species (e.g., electrons, radicals, and ions) accelerated the reduction of MnO4-. The reaction rate as well as the physical and chemical features of resulting products were found to be related to the type of sugars. Their high surface areas (F-MnO2 (169.1 m2·g-1) > G-MnO2 (141.0 m2·g-1) > S-MnO2 (85.5 m2·g-1)) provided efficient capability for the adsorption of cationic dye molecules, i.e., methylene blue. The dye removal efficiencies of all samples were >99% for an initial dye concentration (C0) of 10 mg·L-1 within 2 min and >82% for C0 = 50 mg·L-1 within 30 min. We expect that the synthesis route presented in this study can be extended to the large-scale production of effective adsorbents and to find practical applications for the industrial and green infrastructure.

DOI： 10.1021/acssuschemeng.7b00560

Enhanced degradation of chitosan by applying plasma treatment in combination with oxidizing agents for potential use as an anticancer agent

Chokradjaroen C., Rujiravanit R., Watthanaphanit A., Theeramunkong S., Saito N., Yamashita K., Arakawa R.

Carbohydrate Polymers Vol. 167 page： 1 - 11 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Solution plasma (SP) treatment in combination with oxidizing agents, i.e., hydrogen peroxide (H2O2), potassium persulfate (K2S2O8) and sodium nitrite (NaNO2) were adopted to chitosan degradation in order to achieve fast degradation rate, low chemicals used and high yield of low-molecular-weight chitosan and chitooligosaccharide (COS). Among the studied oxidizing agents, H2O2 was found to be the best choice in terms of appreciable molecular weight reduction without major change in chemical structure of the degraded products of chitosan. By the combination with SP treatment, dilute solution of H2O2 (4–60 mM) was required for effective degradation of chitosan. The combination of SP treatment and dilute solution of H2O2 (60 mM) resulted in the great reduction of molecular weight of chitosan and water-soluble chitosan was obtained as a major product. The resulting water-soluble chitosan was precipitated to obtain COS. An inhibitory effect against cervical cancer cell line (HeLa cells) of COS was also examined.

DOI： 10.1016/j.carbpol.2017.03.006

Crystallinity and surface state of cellulose in wet ball-milling process

Nemoto S., Ueno T., Watthanaphanit A., Hieda J., Saito N.

Journal of Applied Polymer Science Vol. 134 ( 22 ) 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Polymer Science

We report the effect of wet ball-milling process under mild neutral salt conditions on the alteration of crystallinity and surface state of microcrystalline cellulose (MC). The ball-milling experiments were performed when the MC was immersed in H2O, NaCl aqueous solution, and KCl aqueous solution. Two collation groups, i.e., MC immersed in H2O2 and nonimmersed MC were additionally investigated for comparison. Except when H2O2 was present, the highest decrease in the cellulose crystallinity index (CI) was observed in dilute KCl. On the other hand, the CI of wet-milled MC/NaCl was greater than that of the wet-milled MC/H2O, however, still lower than that of the non-immersed MC. XPS results showed that the carbonization progressed in dry-milled MC and wet-milled MC/NaCl surfaces. Though, the surface oxidization progressed in wet-milled MC/H2O and wet-milled MC/KCl. Lastly, the ball-milling processes in different solutions led to various decreases of the crystallinity and the surface degradation due to carbonization and/or oxidization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44903.

DOI： 10.1002/app.44903

The plasma-assisted formation of Ag@Co<inf>3</inf>O<inf>4</inf> core-shell hybrid nanocrystals for oxygen reduction reaction

Kim S.M., Jo Y.G., Lee M.H., Saito N., Kim J.W., Lee S.Y.

Electrochimica Acta Vol. 233 page： 123 - 133 2017.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

In this study, Ag@Co3O4 core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co3O4 core-shell nanocrystals are ca. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the O[sbnd]O bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.

DOI： 10.1016/j.electacta.2017.03.049

Enhanced ferromagnetism in graphite-like carbon layer-coated ZnO crystals

Tu N., Dung N.H., Lan N.T., Nguyen K.T., Dung N.D., Viet D.X., Tuan N.T., Bui H.V., Nam D.V., Huy P.T., Saito N.

Journal of Alloys and Compounds Vol. 695 page： 233 - 237 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

We report on the preparation of graphite-like carbon-coated ZnO nanoparticles by ball milling a powder mixture of ZnO and C. Magnetic measurements indicated that carbon coating can strongly enhance the room-temperature ferromagnetism of ZnO nanoparticles, depending on preparation conditions. This enhancement may stem from robust ferromagnetism at the ZnO/C interface. The origin of interfacial ferromagnetism is attributed to crystallographic defects at the surface of ZnO crystals which are stabilized by the carbon shell layer.

DOI： 10.1016/j.jallcom.2016.10.200

Facile preparation of defective black TiO<inf>2</inf> through the solution plasma process: Effect of parametric changes for plasma discharge on its structural and optical properties

Jedsukontorn T., Ueno T., Saito N., Hunsom M.

Journal of Alloys and Compounds Vol. 726 page： 567 - 577 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Defective TiO2 or black TiO2 nanoparticles (NPs) are remarkably attractive for photocatalytic applications, since the defect-disordered structure crucially affects the optical properties. In this work, high visible light-active black TiO2 NPs were synthesized by an innovative solution plasma process (SPP) with a titanium (Ti) electrode in HNO3 solution. The effects of the plasma operating parameters, in terms of the pulse frequency (20–80 kHz) and pulse width (0.5–2.0 μs) under two different HNO3 concentrations (0.3 mM and 3.0 mM) on the morphology, structural and optical properties of the obtained black TiO2 NPs were explored. Increasing the pulse frequency, pulse width and concentration of HNO3 all increased the input energy per pulse and energy per second, which induced an increased volume-based particle size, synthesis rate and Ti3+/Ti4+ ratio, but decreased the rutile mass fraction, the Ti-OH/TiO ratio and the band gap energy of the obtained black TiO2 NPs. Among all the prepared black TiO2 NP samples, those prepared at a pulse frequency of 20 kHz, pulse width of 2 μs (energy input per second of 17.3 J) in 3.0 mM HNO3 exhibited the highest visible-light absorption capability (the lowest band gap energy of ∼2.44 eV). The variation in the band gap energy was more strongly dependent on the Ti3+/Ti4+ ratio than the Ti-OH/TiO ratio in the structure of black TiO2 NPs.

DOI： 10.1016/j.jallcom.2017.08.028

New insights into vegetable oil pyrolysis by cold plasma technique

Meeprasertsagool P., Watthanaphanit A., Ueno T., Saito N., Reubroycharoen P.

Energy Procedia Vol. 138 page： 1153 - 1158 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Energy Procedia

Green liquid fuels are alternatively produced by pyrolysis of vegetable oil. Still, this process requires high processing temperature and high energy consumption per unit cost. Recently, solution/liquid-phase plasma (cold plasma) is the novel method to provide the direct energy at highly excited energy state. In this study, the investigation of the green fuel synthesis from vegetables oils using cold plasma was examined. The cold plasma reactor was connected to a bipolar pulsed power supply under 200 ml of palm oil, the pulse frequency adjusted from 15-45 kHz and the voltage adjusted in ranges of 1.2-1.5 kV with 40 minutes of discharge times, pulse width 2 μs, electrode distance 0.5 mm. Properties of generated plasma were investigated by optical emission spectroscopy (OES) methods. The liquid products were analysed by GC-MS. In order to identify components of the liquid product, a GC-MS chromatogram was carried out; the main peaks were oleic acid and palmitic acid. Therefore, the other peak showed which products were cracked to short-chain hydrocarbon and hexadecane was one of the compounds which were cracked in palm oil. In conclusion, the results showed that plasma has potential and enough energy to convert vegetable oils in liquid fuels at room temperature which can also provide the direct energy better than pyrolysis.

DOI： 10.1016/j.egypro.2017.10.224

Photocatalytic behavior of metal-decorated TiO<inf>2</inf> and their catalytic activity for transformation of glycerol to value added compounds

Jedsukontorn T., Saito N., Hunsom M.

Molecular Catalysis Vol. 432 page： 160 - 171 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Molecular Catalysis

In this work, TiO2 was decorated with one of four different metals (Bi, Pd, Pt and Au) by sol immobilization at ambient condition. The individual addition of each metals on the TiO2 did not affect the crystallite size or band gap energy of TiO2, but increased its visible light absorption ability due to the localized surface plasmon resonance effect of the doped metals, except for Bi, as well as the mechanism of the charge transfer. Among all the prepared metal-decorated TiO2 photocatalysts, Au/TiO2 exhibited the highest visible light absorption ability and an appropriate mechanism of charge transfer, which consequently alleviated the e−–h+ recombination. It also provided the highest photocatalytic activity for glycerol conversion (92.8% at 14 h) and yield of dihydroxyacetone, glyceraldehyde, glycolic acid, hydroxypyruvic acid and formaldehyde of 12.0, 23.1, 10.7, 13.6 and 15.3%, respectively.

DOI： 10.1016/j.mcat.2017.02.022

Novel synthesis of PtPd nanoparticles with good electrocatalytic activity and durability

Zhang J., Hu X., Yang B., Su N., Huang H., Cheng J., Yang H., Saito N.

Journal of Alloys and Compounds Vol. 709 page： 588 - 595 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

PtPd nanoparticles in the size range of 2–5 nm have been directly synthesized from their metal wire electrodes via a one-step plasma sputtering technique in a solution of water and methanol under atmospheric pressure. PtPd nanoparticles produced in the water/methanol solution have good dispersibility compared with those produced in water because methanol successfully reduces the aggregation of the nanoparticles during the plasma sputtering process. Further, the solution plasma technique provides a novel reaction field with a highly energetic state for the PtPd nanoparticle synthesis. KB-supported PtPd nanoparticles (PtPd/KB, 12 wt% Pt) exhibit excellent electrocatalytic activity (over 4 times mass activity compared with commercial Pt/C) and stability (maintaining 43% mass activity after 300 cycles) towards methanol electrooxidation because of their large electrochemical surface area (ECSA, that is 2.5 times greater than that of commercial Pt/C) and synergistic effect of the binary alloy. Thus, as-synthesized PtPd/KB catalysts may have potential applications in direct methanol fuel cells (DMFCs) to lower their cost and improve their cycle efficiency.

DOI： 10.1016/j.jallcom.2017.03.202

Simple introduction of carboxyl head group with alkyl spacer onto multiwalled carbon nanotubes by solution plasma process

Nemoto S., Ueno T., Watthanaphanit A., Hieda J., Bratescu M.A., Saito N.

Japanese Journal of Applied Physics Vol. 56 ( 9 ) 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

A simple method of fabricating carboxyl-terminated multiwalled carbon nanotubes (MWCNTs) with alkyl spacers was developed to improve the dispersion quality of MWCNTs in aqueous solutions using solution plasma (SP) in a 6-aminocaproic acid solution. The formation of SP in the solution led to better dispersion of MWCNTs in aqueous solutions. Fourier transform infrared spectroscopy (FT-IR) results indicate that a carboxyl group with an alkyl spacer can be introduced by SP treatment in the 6-aminocaproic acid solution. Sedimentation tests show that the SP-treated MWCNTs in the 6-aminocaproic acid solution retained their good dispersion quality in aqueous solutions of pHs 5 6 and 9. The alkyl spacer plays an important role in the preservation of dispersion states particularly at pH 6.

DOI： 10.7567/JJAP.56.096202

Synthesis of carbon nanoparticles from used motor oil and benzene via solution plasma process

Seangarunthong N., Khongthong P., Panomsuwan G., Ueno T., Saito N., Eiad-Ua A.

Key Engineering Materials Vol. 751 KEM page： 773 - 778 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Key Engineering Materials

Carbon nanoparticles (CNPs) were successfully synthesized from the mixture of used motor oil and benzene via a solution plasma process (SPP). The synthesis was achieved within a single step at room temperature and atmospheric pressure. The effects of mixing ratio between used motor oil and benzene on the physical and chemical properties of CNPs were investigated by means of field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy. The results revealed that there were no significant changes in morphological feature and chemical functional groups on CNPs at different mixing ratios. The CNPs exhibited the aggregates of fine particles with the diameter of about 20-30 nm. The crystallinity of CNPs was found to be slightly increased when synthesized under the presence of used motor oil, possibly due to the effect of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in used motor oil. We expect that the conversion of used motor oil into CNPs by SPP could be another attractive way to add the value to used motor oil prior to disposing.

DOI： 10.4028/www.scientific.net/KEM.751.773

Solution plasma synthesis of Pt/ZnO/KB for photo-assisted electro-oxidation of methanol

Hu X., Ge C., Su N., Huang H., Xu Y., Zhang J., Shi J., Shen X., Saito N.

Journal of Alloys and Compounds Vol. 692 page： 848 - 854 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

A high electrocatalytic performance Pt/ZnO/KB is well fabricated by a solution plasma technique in water at atmospheric pressure. Their electrocatalytic performance toward methanol oxidation is evaluated in alkaline with light irradiation or in dark. The electrocatalytic activity of Pt is improved in dark because the distribution and reactive sites of Pt nanoparticles are improved by coupling ZnO. And higher electrocatalytic activity is detected under light irradiation because of synergistic effect of photo- (ZnO) and electro-catalyst (Pt). Compared with several morphologies ZnO, ZnO nanowires give better catalytic activity for methanol oxidation than porous ZnO nanosheets because ZnO nanowires possess better electron transport property and smaller resistance. Under light irradiation, Pt/ZnO/KB coupled with ZnO nanowires shows over 3 times higher catalytic activity (ca. 964 mA mgPt−1) than Pt/KB (ca. 306 mA mgPt−1). And the tolerance to CO-poisoning and stability of Pt/ZnO/KB are also improved. Therefore, Pt/ZnO/KB nanocomposite will be a highly efficient potential anode catalyst in DMFCs with light irradiation.

DOI： 10.1016/j.jallcom.2016.09.032

Solution plasma synthesis of a boron-carbon-nitrogen catalyst with a controllable bond structure

Lee S., Heo Y., Bratescu M.A., Ueno T., Saito N.

Physical Chemistry Chemical Physics Vol. 19 ( 23 ) page： 15264 - 15272 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Synthesis of boron-carbon-nitrogen (BCN) nanocarbon with a controllable bond structure for enhanced oxygen reduction reaction (ORR) activity and durability was performed using a new method of discharge in organic solution mixtures named the 'Solution Plasma Process'. Using selected precursors a new strategy for the simultaneous synthesis of nanocarbon co-doped with heteroatoms was found. The synergistic effect of N and B in an uncoupling bond state improved the formation of new active sites for the ORR performance by changing the electronic structure of the base carbon. Meanwhile, when B and N are bonded together, the BCN catalyst contributes to a reduced ORR activity by forming a balanced electronic structure in carbon. The BCN nanocarbon with an uncoupling bond state exhibits an enhanced ORR activity under alkaline conditions, with an onset potential of -0.25 V versus -0.31 V for B/N coupling and 3.43 transferred electrons during the ORR. Although the ORR activity of the B/N uncoupling nanocarbon was not as good as the typical Pt/C, the durability of this synthesized material (15.1% current decrease after 20000 s of operation) was significantly better than that of the Pt/C catalyst (61.5% current drop under the same conditions). After the durability test, the increase of the chemical states containing oxygen was higher for Pt/C than B/N uncoupling.

DOI： 10.1039/c6cp06063c

In-situ one-step synthesis of carbon-encapsulated naked magnetic metal nanoparticles conducted without additional reductants and agents

Kang J., Kim Y., Kim H., Hu X., Saito N., Choi J., Lee M.

Scientific Reports Vol. 6 2016.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

C-encapsulated highly pure Ni, Co, and Fe magnetic nanoparticles (MNPs/C) were synthesized by an innovative one-step in-situ plasma in liquid method (solution plasma processing, SPP) without any additional reductants, agents, or treatment. Successful encapsulation of MNPs was demonstrated by using inductively coupled plasma-atomic emission spectrometry and cyclic voltammetry techniques. The obtained X-ray diffraction patterns and transmission electron microscopy images corresponded to MNPs with average diameters of 5 nm and good crystalline structure. The C capsules with spherical shapes (containing onion-like layers) were characterized by uniform sizes (ranging from 20 nm to 30 nm) and chain-like morphologies. The synthesized MNPs/C exhibited superparamagnetic properties at room temperature and might be utilized in data storage, biomedical, and energy applications since various NPs (including bimetallic ones) could be easily prepared by changing working electrodes. This study shows the potential of SPP to be a candidate for the next-generation synthesis method of NPs/C.

DOI： 10.1038/srep38652

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes

Morishita T., Ueno T., Panomsuwan G., Hieda J., Yoshida A., Bratescu M., Saito N.

Scientific Reports Vol. 6 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C-H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma-solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.

DOI： 10.1038/srep36880

Effect of electron acceptors H<inf>2</inf>O<inf>2</inf> and O<inf>2</inf> on the generated reactive oxygen species <sup>1</sup>O<inf>2</inf> and OH<sup>·</sup> in TiO<inf>2</inf>-catalyzed photocatalytic oxidation of glycerol

Jedsukontorn T., Meeyoo V., Saito N., Hunsom M.

Cuihua Xuebao/Chinese Journal of Catalysis Vol. 37 ( 11 ) page： 1975 - 1981 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Cuihua Xuebao/Chinese Journal of Catalysis

The effect of the electron acceptors H2O2 and O2 on the type of generated reactive oxygen species (ROS), and glycerol conversion and product distribution in the TiO2-catalyzed photocatalytic oxidation of glycerol was studied at ambient conditions. In the absence of an electron acceptor, only HO· radicals were generated by irradiated UV light and TiO2. However, in the presence of the two electron acceptors, both HO· radical and 1O2 were produced by irradiated UV light and TiO2 in different concentrations that depended on the concentration of the electron acceptor. The use of H2O2 as an electron acceptor enhanced glycerol conversion more than O2. The type of generated value-added compounds depended on the concentration of the generated ROS.

DOI： 10.1016/S1872-2067(16)62519-6

Differences in intermediate structures and electronic states associated with oxygen adsorption onto Pt, Cu, and Au clusters as oxygen reduction catalysts

Morishita T., Ueno T., Panomsuwan G., Hieda J., Bratescu M., Saito N.

Journal of Physics D: Applied Physics Vol. 49 ( 41 ) 2016.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

We used ab initio molecular orbital (MO) calculations to study the differences in the intermediate structures and the electronic states involved in the adsorption of O2 onto 13-atom metal clusters of Pt, Cu, and Au. Additionally, the conditions required for the electrocatalytic oxygen reduction reaction (ORR) on the Pt, Cu, and Au clusters were investigated and discussed. The intermediates involved in O2 adsorption onto Pt, Cu, and Au were found to be (Pt-O)-(Pt-O), Cu-O, and Au-O2, respectively. The differences in the O2 adsorption intermediates is explained on the basis of our analysis of the projected density of state (PDOS) area of the new MOs produced from a mixture of the 2pπ ∗ orbitals of O2 and the d orbitals of the metal clusters. The formation of the (Pt-O)-(Pt-O) intermediate after the adsorption of O2 onto the Pt cluster is attributed to the emergence of an antibonding orbital above the Fermi level. Thus, this electronic state can lead to the decomposition and desorption of O2 molecules, thereby promoting the high-activity level of ORR. For the Cu cluster, a new antibonding orbital was observed below the Fermi level. Moreover, the Cu cluster surface can only promote O2 decomposition and not O2 desorption due to the formation of copper oxides. For the Au cluster, no new MOs related to 2pπ ∗ orbitals of O2 appeared because O2 was molecularly adsorbed, implying that the Au cluster is an inefficient ORR catalyst.

DOI： 10.1088/0022-3727/49/41/415305

Fabrication of bacterial cellulose-ZnO composite via solution plasma process for antibacterial applications

Janpetch N., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 148 page： 335 - 344 2016.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Zinc oxide (ZnO) was successfully synthesized by applying a solution plasma, a plasma discharge in a liquid phase, without the addition of a reducing agent and simultaneously deposited into a bacterial cellulose pellicle that functioned as a template. By the reasons of its nano-sized structure as well as favorable porous configuration, the BC pellicle has been proved to be a splendid upholding template for the coordination of ZnO. In addition, the ZnO-deposited BC composites demonstrated strong antibacterial activity without a photocatalytic reaction against both Staphylococcus aureus and Escherichia coli. Hence, the ZnO-deposited BC composites can be used as an antibacterial material in wound dressing and water disinfection applications.

DOI： 10.1016/j.carbpol.2016.04.066

Heterocarbon nanosheets incorporating iron phthalocyanine for oxygen reduction reaction in both alkaline and acidic media

Hyun K., Ueno T., Panomsuwan G., Li O., Saito N.

Physical Chemistry Chemical Physics Vol. 18 ( 16 ) page： 10856 - 10863 2016.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Heterocarbon nanosheets incorporating iron phthalocyanine (FP-NCNs-SP) have been successfully synthesized by a facile one-pot solution plasma process at high repetition frequency. It was found that the Fe-N4 catalytic active sites could be preserved on the FP-NCNs-SP without degradation. The FP-NCNs-SP also possessed large surface area, good conductivity and high degree of graphitization. Electrochemical evaluations demonstrated that NCNs-SP had excellent electrocatalytic activity and selectivity toward oxygen reduction reaction (ORR) in alkaline medium through a direct four-electron pathway. Although the significant improvement in ORR activity was clearly observed in acidic medium, it was much poorer than in alkaline medium. We believe that the results presented in this work will shed light on the advanced synthesis and design of ORR electrocatalysts at room temperature with an abundance of catalytically active sites and high ORR performance.

DOI： 10.1039/c5cp07739g

High Efficiency DNA Extraction by Graphite Oxide/Cellulose/Magnetite Composites Under Na<sup>+</sup> Free System

Akceoglu G., Li O., Saito N.

JOM Vol. 68 ( 4 ) page： 1071 - 1077 2016.4

Language：English Publishing type：Research paper (scientific journal) Publisher：JOM

DNA extraction is the key step at various research areas like biotechnology, diagnostic development, paternity determination, and forensic science. Solid support extraction is the most common method for DNA purification. In this method, Na+ ions have often been applied as binding buffers in order to obtain high extraction efficiency and high quality of DNA; however, the presence of Na+ ions might be interfering with the downstream DNA applications. In this study, we proposed graphite oxide (GO)/magnetite composite/cellulose as an innovative material for Na+-free DNA extraction. The total wt.% of GO was fixed at 4.15% in the GO/cellulose/magnetite composite. The concentration of magnetite within the composites were controlled at 0–3.98 wt.%. The extraction yield of DNA increased with increasing weight percentage of magnetite. The highest yield was achieved at 3.98 wt.% magnetite, where the extraction efficiency was reported to be 338.5 ng/µl. The absorbance ratios between 260 nm and 280 nm (A260/A280) of the DNA elution volume was demonstrated as 1.81, indicating the extracted DNA consisted of high purity. The mechanism of adsorption of DNA was provided by (1) π–π interaction between the aromatic ring in GO and nucleobases of DNA molecule, and (2) surface charge interaction between the positive charge magnetite and anions such as phosphates within the DNA molecules. The results proved that the GO/cellulose/magnetite composite provides a Na+-free method for selective DNA extraction with high extraction efficiency of pure DNA.

DOI： 10.1007/s11837-016-1826-0

Nitrogen-Doped Carbon Nanoparticle-Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction

Panomsuwan G., Saito N., Ishizaki T.

ACS Applied Materials and Interfaces Vol. 8 ( 11 ) page： 6962 - 6971 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle-carbon nanofiber (NCNP-CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP-CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP-CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP-CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP-CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal-air batteries.

DOI： 10.1021/acsami.5b10493

Electrocatalytic oxygen reduction on nitrogen-doped carbon nanoparticles derived from cyano-aromatic molecules via a solution plasma approach

Panomsuwan G., Saito N., Ishizaki T.

Carbon Vol. 98 page： 411 - 420 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Metal-free nitrogen-doped carbon nanoparticles (NCNPs) have been synthesized via a solution plasma process with the potential to achieve uniformly distributed nitrogen atoms. A set of cyano-aromatic molecules, including benzonitrile, 2-cyanopyridine, and cyanopyrazine, were used as a single-source precursor in the synthesis without the addition of a metal catalyst source. The resultant NCNPs reveal uniformly nanosized particles (20-40 nm) and an interconnected hierarchical pore structure with a high specific surface area (210-250 m2 g-1). The difference in carbon/nitrogen mole ratios of organic precursors gives rise to the variation of nitrogen-doping level in NCNPs from 0.63 to 1.94 atom %. Detailed electrochemical evaluation toward the oxygen reduction reaction (ORR) demonstrates that NCNPs exhibit a significant improvement in terms of both onset potential and current density under alkaline and acidic conditions. The predominant distribution of graphitic-N and pyridinic-N sites on NCNPs plays an essential role in enhancing the ORR activity and the selectivity toward a four-electron reduction pathway. More importantly, NCNPs possess excellent robust long-term durability and strong methanol tolerance compared with those of a commercial Pt/carbon catalyst.

DOI： 10.1016/j.carbon.2015.11.013

Synthesis of Fe-Cu bi-functional catalysts by solution plasma process for li-air battery application

Li O.L., Takahashi R., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 10 ( 1 ) page： 51 - 56 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

This research reported an innovative method to synthesize inexpensive and bi-functional catalyst electrode material for the application in Li-air battery. Non-novel metal, Cu and Fe were served, respectively, as alternative Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). Solution Plasma Process was applied to synthesized Cu-Fe metal nanoparticles and carbon nanoparticles simultaneously. SPP was generated in benzene 100 mL using a bipolar pulse power supply. Iron and copper of diameter 1.0 mm were used for the discharge electrode and precursor of the bimetallic nanoparticles. Solution was reacted and stirred continuously for 20 minutes. Based on the amount of electrode consumption and ICP-AES analysis, the percentage of Cu and Fe supported on carbon were respectively, 2.8 and 1.0 wt%. The diameter of metal nanoparticles was approximately 10 nm, where the carbon nanoparticles ranged between 20-30 nm. From XRD analyses, the presences of Cu, Fe and CuFe2O4 were confirmed. In the performance of cyclic voltammetry, Fe and Cu nanoparticles showed the catalytic activity, respectively, for ORR and OER, at -0.38 and above 0.5 V. In the case of Fe-Cu bimetallic nanoparticles, it showed the combined catalytic activities of the single particles.

Analysis of benzoquinone decomposition in solution plasma process

Bratescu M., Saito N.

Journal of Instrumentation Vol. 11 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Instrumentation

The decomposition of p-benzoquinone (p-BQ) in Solution Plasma Processing (SPP) was analyzed by Coherent Anti-Stokes Raman Spectroscopy (CARS) by monitoring the change of the anti-Stokes signal intensity of the vibrational transitions of the molecule, during and after SPP. Just in the beginning of the SPP treatment, the CARS signal intensities of the ring vibrational molecular transitions increased under the influence of the electric field of plasma. The results show that plasma influences the p-BQ molecules in two ways: (i) plasma produces a polarization and an orientation of the molecules in the local electric field of plasma and (ii) the gas phase plasma supplies, in the liquid phase, hydrogen and hydroxyl radicals, which reduce or oxidize the molecules, respectively, generating different carboxylic acids. The decomposition of p-BQ after SPP was confirmed by UV-visible absorption spectroscopy and liquid chromatography.

DOI： 10.1088/1748-0221/11/01/C01009

Adsorption of carbon dioxide by solution-plasma-synthesized heteroatom-doped carbon nanospheres

Thongwichit N., Helena Li O.L., Yaowarat W., Saito N., Suriyapraphadilok U.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Porous carbon nanospheres (CNSs) synthesized by a plasma-in-liquid technique were applied as an adsorbent for CO2 adsorption. Two different types of aromatic solvents, benzene and pyridine, were used as precursors to generate CNSs. The prepared CNSs were carbonized and then activated with CO2 to obtain carbon materials with a suitable porous structure for CO2 adsorption. To improve CO2 adsorption capacity, activated CNSs were then chemically modified using different approaches of surface treatment, namely, HNO3 oxidation, amination without HNO3 preoxidation, and amination with HNO3 preoxidation. The CO2 adsorption capacities of the samples were investigated at 1 atm and 40 °C using a simultaneous thermal analyzer. It was found that the CO2 adsorption of CNSs was enhanced through the development of textural properties. All of the surface treatment approaches led to the increase in CO2 adsorption capacity of the activated CNSs owing to the presence of nitrogen or oxygen functional groups introduced onto the carbon surface during the treatment.

DOI： 10.7567/JJAP.55.01AE10

Highly durable silica-coated Pt/carbon nanotubes for proton-exchange membrane fuel cells application

Yaowarat W., Helena Li O.L., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Platinum nanoparticles supported on carbon nanotubes (Pt/CNTs) have been used as an electrocatalyst in proton-exchange membrane fuel cells (PEMFCs). These catalysts show higher activity in oxygen reduction reaction in PEMFCs than conventional carbon-black-supported Pt nanoparticles. However, their durability is lower than that of other metal-alloy-based or nonmetal-based catalysts. In this study, Pt/CNTs were synthesized by solution plasma followed by coating with silica layer by the sol-gel method using a cationic surfactant [cetyltrimethylammonium bromide (CTAB)]. This material can be used as a cathode in PEMFCs. The silica layer was coated on the surface of Pt/CNTs to prevent agglomeration and detachment of Pt nanoparticles from carbon nanotubes during operation. The formation of silica layers significantly improved the durability of the Pt/CNT catalysts under acidic conditions. After 300 cycles of the cyclic voltammetry test in 0.5#M sulfuric acid (H2SO4), silicacoated Pt/CNTs increased the durability by 43.0 and 24.0% compared with those of noncoated commercial Pt/C and Pt/CNTs, respectively.

DOI： 10.7567/JJAP.55.01AE23

Synthesis of nitrogen-containing carbon by solution plasma in aniline with high-repetition frequency discharges

Hyun K., Ueno T., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Nitrogen-containing carbon nanoparticles were synthesized in aniline by solution plasma with high-repetition frequency discharges. We developed a bipolar pulsed power supply that can apply high-repetition frequencies ranging from 25 to 200 kHz. By utilizing high-repetition frequencies, conductive carbons were directly synthesized. The crystallinity was increased and H/C ratio of carbon was decreased. Furthermore, nitrogen atoms were simultaneously embedded in the carbon matrix. Due to the presence of nitrogen atoms, the conductivity and electrocatalytic activity of the samples were remarkably improved compared to that of a pure carbon matrix synthesized from a benzene precursor.

DOI： 10.7567/JJAP.55.01AE18

Synthesis of SnO<inf>2</inf> nanoparticles using a solution plasma and their gas-sensing properties

Zhang J., Hu X., Shi J., Lu P., Shen X., Xu P., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

A simple solution plasma method was applied to the synthesis of SnO2 nanoparticles directly from tin(II) chloride solution, without adding any precipitant, stabilizer, or other agents at atmospheric pressure, because solution plasma provides a reaction field with a highly excited energy state. The results of X-ray power diffraction (XRD) analysis and transmission electron microscopy (TEM) verified that well-crystallized SnO2 nanoparticles in the size range of 2-5 nm were synthesized. SnO2 nanoparticles show satisfactory sensitivities to acetaldehyde and ethanol.

DOI： 10.7567/JJAP.55.01AE17

A simple synthesis method for nanostructured Co-WC/carbon composites with enhanced oxygen reduction reaction activity

Kang J., Kim H., Saito N., Lee M.

Science and Technology of Advanced Materials Vol. 17 ( 1 ) page： 37 - 44 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Science and Technology of Advanced Materials

Co nanoparticles (Co NPs) and nanoscale tungsten carbide (WC) are successfully synthesized simultaneously with mesoporous structured carbon black (C) using an innovative simple method, which is known as solution plasma processing (SPP), and NPs are also loaded onto carbon black at the same time by SPP. The introduction of Co NPs led to not only superior oxygen reduction reaction (ORR) activity in terms of onset potential and peak potential, but also to a more efficient electron transfer process compared to that of pure WC. Co-WC/C also showed durability for long-term operation better than that of commercial Pt/C. These results clearly demonstrate that the presence of Co NPs significantly enhanced the ORR and charge transfer number of neighboring WC NPs in ORR activities. In addition, it was proved that SPP is a simple method (from synthesis of NPs and carbon black to loading on carbon black) for the large-scale synthesis of NP-carbon composite. Therefore, SPP holds great potential as a candidate for nextgeneration synthetic methods for the production of NP-carbon composites.

DOI： 10.1080/14686996.2016.1140305

DFT calculation of oxygen adsorption on a core-single shell ZnNb catalyst

Morishita T., Ueno T., Panomsuwan G., Hieda J., Antoaneta Bratescu M., Saito N.

RSC Advances Vol. 6 ( 100 ) page： 98091 - 98095 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Oxygen adsorption onto Pt, Nb, and core-single shell ZnNb particles is studied using ab initio molecular orbital (MO) calculations to realize their ability for the oxygen reduction reaction (ORR). The calculations demonstrate that the electronic state of oxygen adsorption on core-single shell ZnNb is very close to that on Pt, rather than that on Nb. The energy levels of the oxygen 2pσ∗ orbital and the antibonding orbital formed by the oxygen 2pπ∗ and metal d orbitals are different depending on the type of catalyst. In contrast, the energy level of the Nb-O π∗ (O2 2pπ∗ + Nb 4d antibonding) orbital of the core-single shell ZnNb is located at a position close to that of Pt. Our finding suggests that the oxygen adsorbed on the core-single shell ZnNb particle can easily be dissociated and desorbed owing to the disappearance of the interaction between the oxygen and Nb subsurface atoms through the replacement of Zn. We expect that core-single shell ZnNb can be utilized as an efficient and cost-effective catalyst for the ORR in a polymer electrolyte fuel cell.

DOI： 10.1039/c6ra19311k

Enhancement of conductivity in nano carbon balls by the addition of carbon tetrachloride: Via room temperature solution plasma process

Li O.L., Hayashi H., Ishizaki T., Saito N.

RSC Advances Vol. 6 ( 57 ) page： 51864 - 51870 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

The conductivity of carbon nanoballs (CNBs) was enhanced by two orders of magnitude with the addition of carbon tetrachloride through a room temperature solution plasma process without post-heat treatment. The synthesized CNBs demonstrated the lowest resistivity of 8 Ω cm when the ratio of benzene to carbon tetrachloride was adjusted to 3:2. The morphologies from Transmission Electron Microscopy (TEM) showed the benzene-synthesized CNBs appeared as amorphous carbon while CNBs generated from the mixture of carbon tetrachloride and benzene were presented as short range graphite with turbostratic structure. From Raman spectroscopy and X-ray diffraction patterns, the results indicated the transition from amorphous carbon to nanocrystalline-graphite (NCG). From chemical elemental analysis, the hydrogen mole percentage decreased 20-50% when 20-60 vol% of carbon tetrachloride was added into benzene. We expect that this approach can be extended to enhance the conductivity of all kinds of amorphous carbonaceous materials in other synthesis technologies under room temperature.

DOI： 10.1039/c6ra02453j

Effect of treatment time in the Mg(OH)<inf>2</inf>/Mg–Al LDH composite film formed on Mg alloy AZ31 by steam coating on the corrosion resistance

Kamiyama N., Panomsuwan G., Yamamoto E., Sudare T., Saito N., Ishizaki T.

Surface and Coatings Technology Vol. 286 page： 172 - 177 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

The corrosion resistant films were fabricated on Mg alloy AZ31 substrates by steam coating method using Al(NO3)3·9H2O aqueous solution as a steam source. The treatment temperature was maintained at 433 K, while the treatment time was varied at 3, 5, 7 and 9 h. X-ray diffraction (XRD) analysis demonstrated that the coated films were composed of a mixed structure of Mg(OH)2 and Mg–Al layered double hydroxide (Mg–Al LDH) phases. As revealed by the scanning electron microscopy (SEM) observation, the surface of coated films had a good uniformity of changing treatment times. The deposition rate increased exponentially with increasing treatment time. Fourier transform infrared (FT-IR) spectra showed that carbonate and nitrate ions were co-existed in the interlayer of Mg–Al LDH. The potentiodynamic polarization curves of the film coated for 7 h exhibited the lowest corrosion current density, which was almost four orders of magnitude lower than that of bare AZ31. The enhanced corrosion resistance was well consistent with the increase of Mg–Al LDH content in the films.

DOI： 10.1016/j.surfcoat.2015.11.051

Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61

Serizawa A., Iwase Y., Sudare T., Saito N., Kamiyama N., Ishizaki T.

Keikinzoku/Journal of Japan Institute of Light Metals Vol. 66 ( 1 ) page： 9 - 14 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Keikinzoku/Journal of Japan Institute of Light Metals

Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61 (AZX612) were investigated. An extruded and twin-rolled casting magnesium alloys AZX612 were used with a view to better understanding the relationship between microstructure and these properties. The microstructures of the magnesium alloys were characterized by optical microscope (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS). The shapes of compounds in the alloys observed by EDS were significantly different; spherical distribution in grain for the extruded magnesium alloy and preferential formation on grain boundaries for the twin-rolled casting magnesium alloy. The different microstructure of the two alloys resulted in showing the different properties. Immersion test in 5 mass% NaCl aqueous solution revealed that the corrosion rates for the extruded and twin-rolled casting magnesium alloys AZX612 were estimated to be 6.5 and 15.0 mm/year, respectively, indicating that the corrosion resistance of the extruded magnesium alloys AZX612 were more superior than that of the twin-rolled casting one. On the contrary, the heat resistance of the alloy did not change depending on the microstructure.

DOI： 10.2464/jilm.66.9

Fe-N-doped carbon-based composite as an efficient and durable electrocatalyst for the oxygen reduction reaction

Panomsuwan G., Saito N., Ishizaki T.

RSC Advances Vol. 6 ( 115 ) page： 114553 - 114559 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

We herein report the preparation of an Fe-N-doped carbon nanoparticle-carbon nanofiber (Fe-N-CNP-CNF) composite using a solution plasma process followed by heat treatment. The resulting Fe-N-CNP-CNF exhibits excellent catalytic activity, durability, and methanol tolerance for the oxygen reduction reaction (ORR) in an alkaline solution. The enhanced ORR activity of Fe-N-CNP-CNF can reasonably be attributed to the synergistic contributions provided by a high degree of graphitization of CNF, meso/macroporosity of CNP, presence of catalytically active sites for ORR (i.e., graphitic N and Fe-N bond), and existence of carbon-encapsulated Fe/Fe3C particles.

DOI： 10.1039/C6RA24214F

Synthesis of colloidal MnO<inf>2</inf> with a sheet-like structure by one-pot plasma discharge in permanganate aqueous solution

Kim H., Watthanaphanit A., Saito N.

RSC Advances Vol. 6 ( 4 ) page： 2826 - 2834 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Stable colloidal MnO2 - consisting of MnO2 with a sheet-like structure - was synthesized by solution plasma process (SPP). The synthesis was completed in one-step by discharging the plasma in potassium permanganate (KMnO4) aqueous solution without using any dispersants or stabilizers. An alteration of the manganese oxide oxidation state, from MnO4- to MnO2 as a function of the discharge time, was investigated by UV-vis spectroscopy. Morphology and elemental constituents were observed by TEM and EDS mapping. Results indicated that the discharge time was an important feature for the formation of MnO2 in the SPP system. Specifically at neutral pH (pH = 7), MnO4- was completely reduced to MnO2 within a discharge time of 18 min. After that the obtained MnO2 was converted rapidly to Mn2+. To better understand the possible pathways of MnO2 formation by the SPP, we compared aspects of the reaction under different pH conditions. Formation of MnO2 under additional, controlled pH conditions, i.e. 2 and 12, was studied. Results suggested that hydrogen species played a key role for the reduction of MnO4- in the water-based SPP system. In comparison to the existing routes for the synthesis of MnO2 nanosheets with a single or low number of layers, the SPP holds excellent promise as an effective alternative means regarding its simplicity, time-energy preserving, and scalability.

DOI： 10.1039/c5ra20416j

Synthesis of heteroatom-carbon nanosheets by solution plasma processing using: N -methyl-2-pyrrolidone as precursor

Hyun K., Ueno T., Li O., Saito N.

RSC Advances Vol. 6 ( 9 ) page： 6990 - 6996 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Nitrogen-carbon nanosheets (NCNS), composed of multi-layer graphene with turbostratic stacking, were successfully synthesized through a solution plasma processing (SPP) at room temperature and an atmospheric pressure. The plasma was generated in 200 mL of N-methyl-2-pyrrolidone (NMP), which was applied as the carbon and nitrogen precursors. The NCNS presented an electrical resistivity of 0.065 Ω cm, which is comparable with that of N-doped carbon nanofibers (CNFs) and N-doped carbon nanotubes (CNTs). The synthesis rate of NCNS was 20 mg min-1. From the characteristics analyses, NCNS showed the surface area of 277 m2 g-1, a pore volume of 0.95 cm3 g-1 and a moderate nitrogen content of 1.3 at%. The synthesized NCNS also exhibited catalytic activity towards oxygen reduction reaction (ORR). This unique synthesis method can be applicable to synthesize multiple types of heteroatom-carbon nanosheets.

DOI： 10.1039/c5ra23659b

Verification of Radicals Formation in Ethanol-Water Mixture Based Solution Plasma and Their Relation to the Rate of Reaction

Sudare T., Ueno T., Watthanaphanit A., Saito N.

Journal of Physical Chemistry A Vol. 119 ( 48 ) page： 11668 - 11673 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry A

Our previous research demonstrated that using ethanol-water mixture as a liquid medium for the synthesis of gold nanoparticles by the solution plasma process (SPP) could lead to an increment of the reaction rate of ∼35.2 times faster than that in pure water. This drastic change was observed when a small amount of ethanol, that is, at an ethanol mole fraction (χethanol) of 0.089, was added in the system. After this composition, the reaction rate decreased continuously. To better understand what happens in the ethanol-water mixture-based SPP, in this study, effect of the ethanol content on the radical formation in the system was verified. We focused on detecting the magnetic resonance of electronic spins using electron spin resonance spectroscopy to determine the type and quantity of the generated radicals at each χethanol. Results indicated that ethanol radicals were generated in the ethanol-water mixtures and exhibited maximum quantity at the xethanol of 0.089. Relationship between the ethanol radical yield and the rate of reaction, along with possible mechanism responsible for the observed phenomenon, is discussed in this paper.

DOI： 10.1021/acs.jpca.5b07224

Adsorption and desorption of DNA tuned by hydroxyl groups in graphite oxides-based solid extraction material

Akceoglu G., Li O., Saito N.

Colloids and Surfaces B: Biointerfaces Vol. 136 page： 1 - 6 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Colloids and Surfaces B: Biointerfaces

The extraction of DNA is the most crucial method used in molecular biology. Up to date silica matrices has been widely applied as solid support for selective DNA adsorption and extraction. However, since adsorption force of Si. OH functional groups is much greater than that of desorption force, the DNA extraction efficiency of silica surfaces is limited. In order to increase the DNA extraction yield, a new surface with different functional groups which possess of greater desorption property is required. In this study, we proposed cellulose/graphite oxide (GO) composite as an alternative material for DNA adsorption and extraction. GO/Cellulose composite provides the major adsorption and desorption of DNA by C. OH, which belongs to alkyl or phenol type of OH functional group. Compared to Si. OH, C. OH is less polarized and reactive, therefore the composite might provide a higher desorption of DNA during the elution process. The GO/cellulose composite were prepared in spherical structure by mixing urea, cellulose, NaOH, Graphite oxide and water. The concentration of GO within the composites were controlled to be 0-4.15. wt.%. The extraction yield of DNA increased with increasing weight percentage of GO. The highest yield was achieved at 4.15. wt.% GO, where the extraction efficiency was reported as 660.4. ng/μl when applying 2. M GuHCl as the binding buffer. The absorbance ratios between 260. nm and 280. nm (A260/A280) of the DNA elution was demonstrated as 1.86, indicating the extracted DNA consisted of high purity. The results proved that GO/cellulose composite provides a simple method for selective DNA extraction with high extraction efficiency of pure DNA.

DOI： 10.1016/j.colsurfb.2015.07.080

Influences of solution plasma conditions on degradation rate and properties of chitosan

Tantiplapol T., Singsawat Y., Narongsil N., Damrongsakkul S., Saito N., Prasertsung I.

Innovative Food Science and Emerging Technologies Vol. 32 page： 116 - 120 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Innovative Food Science and Emerging Technologies

In this work, the effects of solution plasma conditions on the degradation rate and properties of chitosan are investigated. Various types of electrodes including tungsten (W), copper (Cu), and iron (Fe) were used. The treatment time and the applied pulse frequency of the bipolar supply varied from 0 to 210 min and 15 to 30 kHz, respectively. The plasma-treated chitosan was characterized by GPC, XRD, FT-IR, and fractionation analysis. The results showed that after plasma treatment for 210 min, the molecular weight of chitosan decreased remarkably, when compared to those of untreated samples. The plasma treatment of chitosan using Fe electrode and high pulse frequency strongly promoted the degradation rate of chitosan. The XRD analysis showed that the crystallinity of plasma-treated chitosan was destroyed. FT-IR analysis revealed that the chemical structure of chitosan was not changed by solution plasma treatment. Solution plasma treatment of chitosan using an Fe electrode provided the highest %yield of water-soluble chitosan. Industrial Relevance In this study, the solution plasma process is introduced to treat chitosan in order to prepare low-molecular-weight chitosan. According to our finding, the solution plasma could be a potential method for the preparation of low-molecular-weight chitosan and chitooligosaccharides. Since the solution plasma is generated under mild conditions (i.e.; the reaction proceeds at room temperature and ambient pressure), therefore, it is very attractive for the degradation of polysaccharide polymer and applicable to industrial materials process such as medicine, food, chemical industry, and cosmetics. In addition, we expected that plasma technology could be used instead of conventional enzymatic treatment and chemical treatment which was high cost and contamination process.

DOI： 10.1016/j.ifset.2015.09.014

Route of glycerol conversion and product generation via TiO<inf>2</inf>-induced photocatalytic oxidation in the presence of H<inf>2</inf>O<inf>2</inf>

Jedsukontorn T., Meeyoo V., Saito N., Hunsom M.

Chemical Engineering Journal Vol. 281 page： 252 - 264 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Journal

The objective of this study was to explore the route of glycerol conversion and product generation via the TiO2-induced photocatalytic oxidation in the presence of H2O2. Effects of TiO2 dosage (1-3g/L), H2O2 concentration (0.3-1.5M), light UV intensity (1.1-4.7mW/cm2) and irradiation time (4-8h) on the level of glycerol conversion and product selectivity were identified using a 2k factorial design. It was found that TiO2 and H2O2 played a simultaneous positive effect on the glycerol conversion in the presence of UV-light. Among all investigated parameters, the most important parameter on glycerol conversion and product selectivity was the irradiation time. Glycerol conversion and product generation can proceed via both h+-mediate and radical-mediated routes, but the radical-mediated route was dominant.

DOI： 10.1016/j.cej.2015.06.078

Accelerated nanoparticles synthesis in alcohol-water-mixture-based solution plasma

Sudare T., Ueno T., Watthanaphanit A., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 45 ) page： 30255 - 30259 2015.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

An extraordinary high-speed synthesis of gold nanoparticles (AuNPs) was discovered by synthesizing the AuNPs in ethanol-water mixtures using a solution plasma process (SPP). The influence of the ethanol mole fraction (χethanol) in the ethanol-water mixtures on the reduction rate of gold chloride ions to AuNPs under the SPP system was studied. The results indicated that the reaction rate of the AuNPs synthesis exhibited a maximum value (i.e. 35.2 times faster than in a pure water system) at the significant point where the partial molar volumes of ethanol and water changed drastically.

DOI： 10.1039/c5cp05168a

The Effect of Electrode Gap Distance on the Synthesis of Carbon Materials by Using Solution Plasma Process

Lee H., Ueno T., Saito N.

JOM Vol. 67 ( 11 ) page： 2550 - 2556 2015.10

Language：English Publishing type：Research paper (scientific journal) Publisher：JOM

Carbon nanomaterials were synthesized by using the solution plasma process and the carbon structure was precisely controlled through adjusting electrode gap distances. Transmission electron microscope and diffraction images showed ordered graphitic layers and clear ring patterns when the electrode distance was wider. The measurement of conductive properties has been improved approximately 400 times from 19 k Ω cm to 47 Ω cm, and the C/H ratio from the result of elemental analysis decreased from 0.31 to 0.18 with decreasing resistivity of carbon. These results showed that the electrode distance was an important factor to control the energy input during the synthesis of carbon materials in the plasma/gas zone generated by solution plasma processing and strongly affect the properties of synthesized carbon materials.

DOI： 10.1007/s11837-015-1660-9

Innovative Graphite Oxide-Cellulose Based Material Specific for Genomic DNA Extraction

Akceoglu G.A., Li O.L., Saito N.

JOM Vol. 67 ( 11 ) page： 2557 - 2563 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：JOM

Extraction of genomic DNA from various types of samples is often challenging for commercial silica spin column. In this study, we proposed graphite oxide (GO)/cellulose composite as an alternative material for genomic DNA extraction. The purity of DNA and extraction efficiency were compared to that of commercial silica product. In this study, the total weight % of GO was fixed at 4.15% in GO/Cellulose composite. Chewed gum, nail clip, cigarette bud paper, animal tissue and hair sample were used as various genomic DNA sources for extraction experiments. Among all types of samples, the extraction efficiencies were 4 to 12 times higher than that of commercial silica spin column. The absorbance ratio of 260 nm to 280 nm (A260/A280) of all samples ranged between 1.6 and 2.0. The results demonstrated that GO/Cellulose composites might serve as an innovative solid support material for genomic DNA extraction.

DOI： 10.1007/s11837-015-1610-6

Electrocatalytic oxygen reduction activity of boron-doped carbon nanoparticles synthesized via solution plasma process

Panomsuwan G., Saito N., Ishizaki T.

Electrochemistry Communications Vol. 59 page： 81 - 85 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochemistry Communications

The synthesis of boron-doped carbon nanoparticles (BCNP) has been achieved through a solution plasma process without the addition of a metal catalyst source using a mixture of benzene and triphenyl borate as precursor. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of BCNP can be improved in terms of onset potential and current density compared to that of undoped carbon nanoparticles in alkaline solution. Moreover, BCNP possesses superior long-term durability and tolerance to methanol oxidation in the ORR.

DOI： 10.1016/j.elecom.2015.07.005

Thermal plasma treatment of stormwater sediments: Comparison between DC non-transferred and partially transferred arc plasma

Li O.L., Guo Y., Chang J.S., Saito N.

Environmental Technology (United Kingdom) Vol. 36 ( 13 ) page： 1672 - 1679 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Environmental Technology (United Kingdom)

The disposal of enormous amount of stormwater sediments becomes an emerging worldwide problem. Stormwater sediments are contaminated by heavy metals, phosphorus, trace organic and hydrocarbons, and cannot be disposed without treatment. Thermal plasma decontamination technology offers a high decomposition rate in a wide range of toxic organic compound and immobilization of heavy metal. In this study, we compared the treatment results between two different modes of thermal plasma: (1) a non-transferred direct current (DC) mode and (2) a partial DC-transferred mode. The reductions of total organic carbon (TOC) were, respectively, 25% and 80% for non-transferred and partially transferred plasma, respectively. Most of the toxic organic compounds were converted majorly to CxHy. In the gaseous emission, the accumulated CxHy, CO, NO and H2S were significantly higher in partially transferred mode than in non-transferred mode. The solid analysis demonstrated that the concentrations of Ca and Fe were enriched by 500% and 40%, respectively. New chemical compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed after treatment in partially DC-transferred mode. The power inputs were 1 and 10 kW, respectively, for non-transferred DC mode and a partially DC-transferred mode. With a lower energy input, non-transferred plasma treatment can be used for decontamination of sediments with low TOC and metal concentration. Meanwhile, partially transferred thermal plasma with higher energy input is suitable for treating sediments with high TOC percentage and volatile metal concentration. The organic compounds are converted into valuable gaseous products which can be recycled as an energy source.

DOI： 10.1080/09593330.2014.1003981

Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity

Panomsuwan G., Watthanaphanit A., Ishizaki T., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 21 ) page： 13794 - 13799 2015.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Black titania spheres (H-TiO<inf>2-x</inf>) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO<inf>2-x</inf>, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO<inf>2-x</inf> can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti<sup>3+</sup> sites.

DOI： 10.1039/c5cp00171d

Simple one-step synthesis of fluorine-doped carbon nanoparticles as potential alternative metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Saito N., Ishizaki T.

Journal of Materials Chemistry A Vol. 3 ( 18 ) page： 9972 - 9981A 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A

Fluorine-doped carbon nanoparticles (FCNPs) were synthesized via a simple one-step solution plasma process for the first time. This synthesis strategy can be achieved at relatively low temperature and atmospheric pressure without the involvement of a metal catalyst. A mixture of toluene (C<inf>6</inf>H<inf>5</inf>CH<inf>3</inf>) and trifluorotoluene (C<inf>6</inf>H<inf>5</inf>CF<inf>3</inf>) was used as a precursor for the synthesis. The fluorine doping content can be varied from 0.95 to 4.52 at%, depending on the precursor mixing ratio. The structural analyses reveal that FCNPs mainly exhibit a disordered amorphous structure. The incorporation of fluorine atoms results in the creation of more defect sites and disordered structure in the carbon particles. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of FCNPs in an alkaline solution shows a significant improvement with increasing fluorine doping content, as reflected in an increased limiting current density and a positively shifted onset potential. In association with X-ray photoelectron spectroscopy (XPS) analysis, an improved ORR activity is possibly attributed to the intercalation of ionic C-F and semi-ionic C-F bonds in the carbon structure. In addition, FCNPs possess excellent long-term operation durability and strong tolerance to methanol oxidation compared to those of a commercial Pt-based catalyst. Our results from this study not only confirm the applicability of the solution plasma process to the synthesis of FCNPs with a controllable fluorine doping level but also provide detailed information of FCNPs as potential alternative ORR catalysts for the electrocatalysis research.

DOI： 10.1039/c5ta00244c

A new approach of nonpoint source pollution/stormwater sludge treatment by an integrated thermal plasma system

Li O.L., Guo Y., Chang J.S., Urashima K., Saito N.

International Journal of Environmental Science and Technology Vol. 12 ( 5 ) page： 1769 - 1778 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Environmental Science and Technology

In this study, we designed and demonstrated the effectiveness of an integrated waste treatment system for contaminated stormwater sludge. The system is comprised of two components: pulsed arc electrohydraulic discharge (PAED) for aqueous-phase treatment and thermal plasma decontamination for solid-phase treatment. PAED provided a reduction of 80 % in total organic carbon (TOC) within a treatment time of 5 min in the aqueous phase. With a prolonged treatment of 30 min, the decontamination of TOC reached over 90 % in the aqueous phase, accompanied with 20 % carbon and 70 % sulfur decreases in weight in the solid phase. A huge weight reduction can be achieved prior to further solid treatment. The solid phase, named as the PAED-treated sludge, was separated by sedimentation and transferred to thermal plasma treatment. The thermal plasma-treated sludge was slightly melted, and the formation of slag was possible. X-ray energy dispersion solid analysis showed that carbon and sulfur were reduced to zero after treatment. Si, Mg, and Al decreased by 25, 30, and 60 %, respectively, while Ca and Fe enriched by 400 and 25 %, respectively. The emission gas analyses demonstrated a possible energy recovery from gaseous compounds with adequate gaseous treatment devices. This research demonstrates an innovative treatment approach of various sludge types, especially those types that contain high water contents and are severely contaminated by toxic organic compounds.

DOI： 10.1007/s13762-014-0570-7

Nitrogen-doped carbon nanoparticles derived from acrylonitrile plasma for electrochemical oxygen reduction

Panomsuwan G., Saito N., Ishizaki T.

Physical Chemistry Chemical Physics Vol. 17 ( 9 ) page： 6227 - 6232 2015.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Nitrogen-doped carbon nanoparticles were synthesized via a solution plasma process, with acrylonitrile as a single-source precursor, followed by a post-thermal annealing process. The nitrogen-bonding states can be tuned by varying the annealing temperature. The best electrocatalytic activity for oxygen reduction reaction (ORR) in terms of both onset potential and limiting current density can be achieved for the catalyst annealed at an optimal temperature of 800 °C because of the high content of graphitic-N catalytic sites and a large specific surface area.

DOI： 10.1039/c4cp05995f

One-step facile synthesis of carbon-supported PdAu nanoparticles and their electrochemical property and stability

Hu X., Shi J., Zhang J., Tang W., Zhu H., Shen X., Saito N.

Journal of Alloys and Compounds Vol. 619 page： 452 - 457 2015.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Well-crystallized PdAu nanoparticles supported on Ketjen Black (KB) were successfully fabricated when both Pd and Au wires were served as the electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of PdAu nanoparticles was almost simultaneous with their dispersion on KB. As-obtained PdAu nanoparticles were confirmed to be alloy by ultraviolet-visible spectrophotometer, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) of each particle. PdAu nanoparticles with the average diameter of 2-5 nm were equably distributed on KB. PdAu nanoparticles showed good electrocatalytic activity both in acidic and alkaline solution corresponding to their obvious oxidation and reduction features. PdAu nanoparticles have improved electrochemical stability compared with the electrochemical properties of Pd and Au nanoparticles mixture after long time multi-scan cyclic voltammetry. Multi-scan cyclic voltammetry also presented the PdAu nanoparticles in alkaline solution have better stability than that in acidic solution. Thus as-obtained PdAu alloy nanoparticles would become a promising electrocatalysts for fuel cells or Li-air batteries. This novel process showed its potential applications in designing optimization of catalysts for fuel cells or Li-air batteries in future.

DOI： 10.1016/j.jallcom.2014.09.051

Enhancement of ORR catalytic activity by multiple heteroatom-doped carbon materials

Kim D., Li O., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 1 ) page： 407 - 413 2015.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Heteroatom-doped carbon matrices have been attracting significant attention due to their superior electrochemical stability, light weight and low cost. Hence, in this study, various types of heteroatom, including single dopants of N, B and P and multiple dopants of B-N and P-N with a carbon matrix were synthesized by an innovative method named the solution plasma process. The heteroatom was doped into the carbon matrix during the discharge process by continuous dissociation and recombination of precursors. The chemical bonding structure, ORR activity and electrochemical performance were compared in detail for each single dopant and multiple dopants. According to the Raman spectra, the carbon structures were deformed by the doped heteroatoms in the carbon matrix. In comparison with N-doped structures (NCNS), the ORR potential of PN-doped structures (PNCNS) was positively shifted from -0.27 V to -0.24 V. It was observed that doping with N decreased the bonding between P and C in the matrix. The multiple doping induced additional active sites for ORR which further enhanced ORR activity and stability. Therefore, PNCNS is a promising metal-free catalyst for ORR at the cathode in a fuel cell.

DOI： 10.1039/c4cp03868a

Communication-In situ formation of anticorrosive Mg(OH)<inf>2</inf>/Carbon composite film on magnesium alloy by ascorbic acid-assisted hydrothermal process

Ishizaki T., Kamiyama N., Yamamoto E., Kumagai S., Sudare T., Saito N.

Journal of the Electrochemical Society Vol. 162 ( 14 ) page： C741 - C743 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society

An Mg(OH)2/carbon composite film was prepared on magnesium alloy AZ31 by an ascorbic acid (AA)-assisted hydrothermal method. All films were composed of crystalline brucite type Mg(OH)2. Film thickness decreased with an increase in the amount of AA added. X-ray photoelectron spectroscopy studies revealed that a peak component related to sp2-hybridized carbons contributed to improve film conductivity. Film resistivity decreased with an increase in C content. The film obtained from the aqueous solution containing 10 g/L of AA showed the lowest corrosion current density of all samples.

DOI： 10.1149/2.0351514jes

Direct deposition of gold nanoparticles on cellulose fiber by solution plasma process

Nemoto S., Watthanphanit A., Saito N.

Materials Research Society Symposium Proceedings Vol. 1723 page： 1 - 7 2015

From Cyano-aromatic Molecules to Nitrogen-doped Carbons by Solution Plasma for the Oxygen Reduction Reaction in Alkaline Medium

Panomsuwan G., Saito N., Ishizaki T.

Materials Today: Proceedings Vol. 2 ( 8 ) page： 4302 - 4308 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today: Proceedings

Nitrogen-doped carbon nanoparticles (NCNPs) were synthesized by a solution plasma process followed by a thermal annealing at 900°C. Cyano-aromatic molecules, including cyanobenzene (C7H5N), 2-cyanopyridine (C6H4N2), and cyanopyrazine (C5H3N3), were used as single source precursors for the synthesis. The morphological features of NCNPs were governed by the aggregates and agglomerates of uniform nanosized particles (20-40nm). The structural analyses confirmed that NCNPs mainly exhibited a disordered amorphous carbon structure. The nitrogen doping contents determined from an X-ray photoelectron spectroscopy were found to be 0.58, 1.36, and 1.29 at% for NCNPs synthesized from cyanobenzene, 2-cyanopyridine, and cyanopyrazine, respectively. The improvements of oxygen reduction reaction activity and selectivity toward a four-electron pathway in an alkaline solution of NCNPs were correlated with the nitrogen doping content and nitrogen bonding state. The NCNPs also possessed excellent long-term durability and strong methanol tolerance in an alkaline solution compared to those of a commercial Pt/carbon catalyst.

DOI： 10.1016/j.matpr.2015.09.017

In situ solution plasma synthesis of mesoporous nanocarbon-supported bimetallic nanoparticles

Kang J., Saito N.

RSC Advances Vol. 5 ( 37 ) page： 29131 - 29134 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Herein, is reported a novel in situ one-step synthesis method of bimetallic nanoparticles (NPs) supported on carbon black, which can markedly prevent the aggregation and growth of NPs, resulting in a small particle size (average 5 nm), good dispersion, and high-electrocatalytic-activity. This journal is

DOI： 10.1039/c5ra04220h

Highly durable silica coated Pt/Cs with different surfactant types for proton exchange membrane fuel cell applications

Yaowarat W., Li O., Saito N.

RSC Advances Vol. 5 ( 55 ) page： 44258 - 44262 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Platinum supported on carbon Vulcan XC-72 (Pt/Cs) for application as a cathode in proton exchange membrane fuel cells (PEMFCs) was coated with silica layers by a sol-gel method with three types of surfactants with different charging properties. The three various types of surfactants (1) cationic surfactant (cetyltrimethylammonium bromide (CTAB)), (2) anionic surfactant (sodium dodecylbezenesulfonate (SDBS)), and (3) non-ionic surfactant (Pluronic 123 (P123)) were applied to prevent agglomeration of the Pt nanoparticles and prevent detachment of the Pt nanoparticles from the carbon supports during operation. The degree of improvement depended on the type of surfactant applied in the sol-gel method. The formation of silica layers by SDBS and P123 significantly improved the durability of the Pt/Cs catalysts under acid conditions. Silica coated Pt/Cs formed using SDBS and P123 showed improved durability after 500 cycles in a cyclic voltammetry test in 0.5 M sulfuric acid (H<inf>2</inf>SO<inf>4</inf>) by 27.3% and 22.7%, respectively.

DOI： 10.1039/c5ra03343h

Cellulose conversion to sugar alcohol by solution plasma processing

Watthanaphanit A., Lee H., Saito N.

Materials Research Society Symposium Proceedings Vol. 1745 page： 22 - 27 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Cellulose was selectively converted to sugar alcohols (sorbitol and mannitol) over a supported-metal catalyst ruthenium on carbon (RuJC) by the application of plasma in cellulose aqueous suspension. Generally, conversion of cellulose to sugar alcohol should be done under H2 pressure and high temperature. The goal of using solution plasma process (SPP) in this study is to initiate "self-hydrogenation" by reactive hydrogen species generated from the plasma due to dissociation of water medium. The sugar alcohols were produced at room temperature and atmospheric pressure. Electrospray ionization mass spectrometric analysis indicates that the SPP is a potent tool to promote the conversion of cellulose to sugar alcohols.

DOI： 10.1557/opl.2015.787

A study on electron impact dissociative ionization of organosilicon precursors for plasma processing

Yun Y., Lee M., Inoue Y., Saito N., Takai O.

Journal of Nanoscience and Nanotechnology Vol. 14 ( 12 ) page： 9653 - 9656 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology

We discussed the electron impact dissociation behavior of the organosilicon molecules with methyl groups, based on the fragment pattern and molecular-orbital calculation of the bond dissociation energies for the molecules. From the calculation of bond dissociation energy of the organosilicon molecules, methyl groups, which bonded directly to the silicon atom, were found to have the weakest. Regarding the fragment patterns of the reactants investigated by a quadrupole mass spectrometer, the hexamethyldisiloxane was harder to dissociate than the trimethylmethoxysilane due to the strong Si-O bonding force, which also affected the dissociation in the plasma. From the above considerations, dissociation reactions by electron impact could be partly identified.

DOI： 10.1166/jnn.2014.10175

One-step facile synthesis of Pd nanoclusters supported on carbon and their electrochemical property

Shi J., Hu X., Zhang J., Tang W., Li H., Shen X., Saito N.

Progress in Natural Science: Materials International Vol. 24 ( 6 ) page： 593 - 598 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Natural Science: Materials International

Well-crystallized Pd nanoclusters supported on Ketjen Black (KB) were successfully fabricated when Pd wires were served as an electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of Pd nanoclusters was almost simultaneous with their dispersion on KB. Pd nanoclusters with the average diameter of about 2. nm were equably distributed on KB, and showed good electrochemical property corresponding to their obvious characteristic peaks. Multi-scan cyclic voltammetry and chronoamperometry clarified that as-prepared Pd nanoclusters have better electrochemical stability in alkaline solution than that of in acidic solution. Thus as-obtained Pd nanoclusters would become a promising electrocatalyst for fuel cells or Li-air batteries.

DOI： 10.1016/j.pnsc.2014.10.011

In situ solution plasma synthesis of nitrogen-doped carbon nanoparticles as metal-free electrocatalysts for the oxygen reduction reaction

Panomsuwan G., Chiba S., Kaneko Y., Saito N., Ishizaki T.

Journal of Materials Chemistry A Vol. 2 ( 43 ) page： 18677 - 18686 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A

We report the in situ synthesis of nitrogen-doped carbon nanoparticles (NCNPs) by a solution plasma process without the addition of metal catalysts. Organic liquid mixtures of benzene and pyrazine were used as the precursors for the synthesis. The nitrogen-doping content can be easily controlled by changing the amount of pyrazine in the precursor. The NCNPs synthesized from the solution plasma process exhibit a turbostratic structure with highly uniform nanoscale particles. The nitrogen atoms can be homogeneously incorporated into the entire carbon structure due to the in situ doping during the growth and formation of the carbon particles. The electrochemical activity toward the oxygen reduction reaction (ORR) of the NCNPs in an alkaline medium reveals the improvement in terms of both the onset potential and current density as the nitrogen-doping content increases. The enhanced ORR activity of the NCNPS is mainly attributed to the presence of pyridinic-N and graphitic-N bonding configurations. They also possess long-term durability and excellent tolerance to methanol crossover effects. The results obtained in this study have demonstrated that the solution plasma process has great potential for the synthesis of metal-free nitrogen-doped carbon electrocatalysts for the ORR. We expect that this approach can be extended to the synthesis of other heteroatom-doped carbonaceous materials for a broad range of research applications in energy conversion and storage.

DOI： 10.1039/c4ta03010a

Solution plasma synthesis of nitrogen-doped carbon nanoballs as effective metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Chiba S., Saito N., Ishizaki T.

Prehospital and Disaster Medicine Vol. 1641 ( 4 ) 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Prehospital and Disaster Medicine

Nitrogen-doped carbons nanoballs were synthesized from an organic liquid precursor (a mixture of benzene and pyrazine) by solution plasma process. After synthesis, they were further annealed at 700 and 900 °C under N2 atmosphere. The nitrogen-doped carbon nanoballs before and after thermal annealing process exhibit a similar morphological feature, and their diameters are in the range between 20 and 40 nm. With higher annealing temperature, the graphitization of the nitrogen-doped carbon nanoballs increases. For the electrocatalytic activity in an alkaline solution, the limiting current density and onset potential for the ORR activity can be significantly improved for the samples after thermal annealing at 900 °C. We anticipate that solution plasma process will be a viable alternative way for synthesizing heteroatom-doped carbon electrocatalysts for broad application in the field of fuel cells, metal-air batteries, and supercapacitors.

DOI： 10.1557/opl.2014.319

Influence of the discharge time of solution plasma process on the formation of gold nanoparticles in alginate matrix

Watthanaphanit A., Heo Y.K., Saito N.

Journal of the Taiwan Institute of Chemical Engineers Vol. 45 ( 6 ) page： 3099 - 3103 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Taiwan Institute of Chemical Engineers

Gold nanoparticles (AuNPs) stabilized in alginate matrix were synthesized by applying the plasma into alginate aqueous solution containing gold(III) chloride trihydrate precursor. Effect of the solution plasma process (SPP) discharge time on the physical properties, including shape and size, and the optical absorption properties of the synthesized AuNPs were investigated by varying the discharge times to be 0, 5, 10, 20 and 30. min. Results reveal that the increase in the discharge time leads to a size reduction of the AuNPs. Also, the particles tend to be more spherical. Appearance of the obtained AuNPs-alginate suspensions along with the change in their UV-vis absorption spectra intensity after samples were left standing for several time intervals suggest that alginate solution itself can act both as a stabilizer and a reducing agent for the AuNPs formation while the application of plasma helps to improve the controllability of shape and size of the synthesized particles. Furthermore, the method is simple, reproducible, and does not need any manipulative skill. Since the reducing agent is not required, the method is suitable for utilizing in biomedical application.

DOI： 10.1016/j.jtice.2014.09.001

Effect of growth temperature on structural and morphological evolution of epitaxial SrTiO<inf>3</inf> thin films grown on LaAlO<inf>3</inf> (001) substrates by ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Vacuum Vol. 109 page： 175 - 179 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Vacuum

A series of epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates by ion beam sputter deposition (IBSD) at various growth temperatures in the range of 350-800 °C. Our results have shown that the growth temperature plays an essential role in influencing the structural and morphological evolution of the STO thin films. X-ray structural analysis demonstrates that the STO thin films are grown under in-plane compressive strain due to the effect of lattice mismatch. The out-of-plane lattice constant is found to decrease with increasing growth temperature. Atomic force microscopy observation reveals that the growth mode of STO thin films transforms from a three-dimensional island mode to a two-dimensional layer-by-layer mode at a sufficiently high growth temperature of 750 °C. We believe that high-quality epitaxial STO thin films with atomically flat surface prepared by IBSD in this study would be beneficial for the fabrication of perovskite STO-based superlattices. © 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2014.07.007

Hierarchical meso-macro structure porous carbon black as electrode materials in Li-air battery

Kang J., Li O.L., Saito N.

Journal of Power Sources Vol. 261 page： 156 - 161 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Power Sources

A new class of hierarchical structure porous carbon black, carbon nanoballs (CNBs), was generated by solution plasma process (SPP) with benzene. The structural characterization revealed that CNBs have excellent meso-macro hierarchical pore structure, with an averaged diameter size of 14.5 nm and a total pore volume of 1.13 cm3 g-1. The CNBs are aggregated forming inter-connected pore channels in different directions on both the meso- and macrometer length scales. The discharge capacity of CNBs reached 3600 mAh g-1, which exceeded the capacity of Ketjen Black EC-600JD (a commercial carbon black with highest cell performance) by 30-40%. The excellent discharge capacity was contributed by the co-existence of high pore volume and meso-macro hierarchical porous structure. This new class carbon material exhibited higher discharge capacity compared to commercial porous carbon materials, and is possible to apply as the next generation of electrode materials in lithium-air (Li-air) battery. The structural and electrochemical properties accompanied with the synthesis mechanism of CNBs were discussed in details. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2014.03.072

Plasma-induced synthesis of CuO nanofibers and ZnO nanoflowers in water

Hu X., Zhang X., Shen X., Li H., Takai O., Saito N.

Plasma Chemistry and Plasma Processing Vol. 34 ( 5 ) page： 1129 - 1139 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Chemistry and Plasma Processing

Fiber-shaped cupric oxide (CuO) nanoparticles and flower-shaped ZnO nanoparticles were facilely synthesized by plasma-induced technique directly from copper and zinc electrode pair in water, respectively. The phase composition, morphologies and optical property of nanoparticles have been investigated by energy dispersive X-ray analysis, X-ray powder diffraction, transmission electron microscopy and UV-vis. The in situ analysis by an optical emission spectroscopy clarified the formation mechanism. Plasma was generated from the discharge between a metal electrode pair in water by a pulse direct current power. CuO and ZnO nanoparticles were synthesized via almost the same formation mechanism, which were prepared via the rapid energetic radicals' bombardment to electrodes' surface, atom vapour diffusion, plasma expansion, solution medium condensation, and in situ oxygen reaction and further growth. This novel plasma-induced technique will become a potential application in nanomaterials synthesis. © 2014 Springer Science+Business Media New York.

DOI： 10.1007/s11090-014-9546-0

X-ray analysis of strain distribution in two-step grown epitaxial SrTiO<inf>3</inf> thin films

Panomsuwan G., Takai O., Saito N.

Applied Physics Letters Vol. 105 ( 5 ) 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150°C prior to growing the STO main layer at 750°C. The thickness of the STO buffer layer was varied at 3, 6, and 10nm, while the total film thickness was kept constant at approximately 110nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4892827

Controlled crystalline orientation of SrTiO<inf>3</inf> thin films grown on Pt(1 1 1)/Ti/α-Al<inf>2</inf>O<inf>3</inf>(0 0 0 1) substrates: Effect of growth temperature and Ti layer thickness

Panomsuwan G., Takai O., Saito N.

Applied Surface Science Vol. 309 page： 95 - 105 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

SrTiO3 (STO) thin films were grown on Pt(1 1 1)/Ti/α-Al2O3(0 0 0 1) substrates by ion beam sputter deposition. Growth temperature was varied between 600 and 750 °C, while Ti layer thickness was adjusted from 3 to 36 nm. Experimental results demonstrate that both the crystalline orientation and surface morphology are significantly dependent on change in the growth temperature and Ti layer thickness. From X-ray structural analysis, the STO thin films grown at 600 °C are perfectly (1 1 0)-oriented in spite of the change in Ti layer thickness. The STO thin films with a perfect (1 1 1) orientation are achievable at a sufficiently high growth temperature (≥700 °C) and a thin Ti layer (3-6 nm). Each crystalline orientation of STO thin films has a specific in-plane orientation relationship with respect to the Pt(1 1 1) layer. Flat-, rod-, and triangle-shaped grains are clearly observed from atomic force microscopy investigation, which are associated with the (1 1 0)-, (1 0 0)-, and (1 1 1)-oriented grains, respectively. Their grain orientations also show a good correlation with the X-ray structural analysis. The growth mechanism of each crystalline orientation can be described in term of surface diffusion, surface energy anisotropy, electrostatic, and role of TiOx seeds. © 2014 Elsevier B.V.

DOI： 10.1016/j.apsusc.2014.04.186

The role of the central Fe atom in the N<inf>4</inf>-macrocyclic structure for the enhancement of oxygen reduction reaction in a heteroatom nitrogen-carbon nanosphere

Kim D.W., Li O.L., Saito N.

Physical Chemistry Chemical Physics Vol. 16 ( 28 ) page： 14905 - 14911 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

In the present work, we demonstrated the significance of a central transition metal, Fe, in a N4-macrocycle for the enhancement of ORR activity and other electrochemical properties. The catalysts were synthesized by a solution plasma process. Fe-phthalocyanine/benzene and phthalocyanine/benzene were chosen as the precursors of Fe-phthalocyanine based mesoporous carbon (FP-MCS) and phthalocyanine based mesoporous carbon (P-MCS) catalysts, respectively. The existence of Fe-N4 and N4 macrocyclic structures was confirmed by X-ray photoelectron spectroscopy. From the chemical bonding structure, FP-MCS demonstrated that the Me-N peaks increased as the amount of iron-phthalocyanine introduced in the experiment increased. The dominant active site was shifted from pyridinic nitrogen to Me-N when iron-phthalocyanine was present. The analysis of Tof-SIMS indicated that the relative intensity of FeN4Cy+ ions was approximately 50% of the total amount of ionized species of ∑FeN xCy+. Both XPS and Tof-SIMS results confirmed that the Fe-N4 site was the most favourable structure in the matrix. From CV measurements, the cathodic peak current corresponding to ORR activity slightly shifted from -0.19 V to -0.17 V when the active site changed from N4 to Fe-N4 macrocyclic structure. The current density increased more than 30% in the presence of iron. Based on the calculation of Koutecky-Levich plots, the electron transfer numbers for ORR reaction in P- and FP-MCSs were 3.25 and 3.98, respectively. These results clearly demonstrated that the presence of a Fe central ion in the N4-macrocyclic structure significantly enhanced the ORR and charge transfer number in ORR activities. © the Partner Organisations 2014.

DOI： 10.1039/c4cp01406e

Synthesis of mono-dispersed nanofluids using solution plasma

Heo Y., Bratescu M., Ueno T., Saito N.

Journal of Applied Physics Vol. 116 ( 2 ) 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

Small-sized and well-dispersed gold nanoparticles (NPs) for nanofluidics have been synthesized by electrical discharge in liquid environment using termed solution plasma processing (SPP). Electrons and the hydrogen radicals are reducing the gold ions to the neutral form in plasma gas phase and liquid phase, respectively. The gold NPs have the smallest diameter of 4.9nm when the solution temperature was kept at 20°C. Nucleation and growth theory describe the evolution of the NP diameter right after the reduction reaction in function of the system temperature, NP surface energy, dispersion energy barrier, and nucleation rate. Negative charges on the NPs surface during and after SPP generate repulsive forces among the NPs avoiding their agglomeration in solution. Increasing the average energy in the SPP determines a decrease of the zeta potential and an increase of the NPs diameter. An important enhancement of the thermal conductivity of 9.4% was measured for the synthesized nanofluids containing NPs with the smallest size. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4887806

Growth of highly (100)-oriented SrTiO <inf>3</inf> thin films on Si(111) substrates without buffer layer

Panomsuwan G., Takai O., Saito N.

Journal of the American Ceramic Society Vol. 97 ( 5 ) page： 1383 - 1385 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the American Ceramic Society

The SrTiO3 (STO) thin films were directly grown on Si(111) substrates without buffer layer by an electron-cyclotron-resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X-ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate-shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current-voltage characteristics of the Au/STO/Si(111) metal-insulator-semiconductor capacitors are investigated and discussed in considerable detail. © 2014 The American Ceramic Society.

DOI： 10.1111/jace.12912

Erratum: A phonon thermodynamics approach of gold nanofluids synthesized in solution plasma (Applied Physics Letters (2014) 104 (111902))

Heo Y., Antoaneta Bratescu M., Aburaya D., Saito N.

Applied Physics Letters Vol. 104 ( 14 ) 2014.4

A phonon thermodynamics approach of gold nanofluids synthesized in solution plasma

Kang Heo Y., Antoaneta Bratescu M., Aburaya D., Saito N.

Applied Physics Letters Vol. 104 ( 11 ) 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

The phonon thermodynamics theory for liquids was applied to explain the thermal characteristics of gold nanofluids synthesized by a simple, one-step, and chemical-free method using an electrical discharge in a liquid environment termed solution plasma process. The specific heat capacity of nanofluids was measured with a differential scanning calorimeter using the ratio between the differential heat flow rate and the heating rate. The decrease of the specific heat capacity with 10% of gold nanofluids relative to water was explained by the decrease of Frenkel relaxation time with 22%, considering a solid-like state model of liquids. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4868872

Depolymerization of chitosan-metal complexes via a solution plasma technique

Pornsunthorntawee O., Katepetch C., Vanichvattanadecha C., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 102 ( 1 ) page： 504 - 512 2014.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Chitosan-metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag +, Zn2+, Cu2+, and Fe3+ ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu2+ or Fe3+ ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan-Ag+ and chitosan-Zn2+ complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan-metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan-Fe3+ complex with the plasma treatment time of 180 min. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbpol.2013.11.025

A novel one-step synthesis of gold nanoparticles in an alginate gel matrix by solution plasma sputtering

Watthanaphanit A., Panomsuwan G., Saito N.

RSC Advances Vol. 4 ( 4 ) page： 1622 - 1629 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

We report a novel strategy to produce stable colloidal gold nanoparticles (AuNPs) in alginate aqueous solution which can be done in one step and without any chemicals. The AuNPs were produced by applying a voltage across a pair of gold electrodes which were immersed in alginate aqueous solution. Since the generation of AuNPs was caused by the sputtering of gold electrodes, the process was named the solution plasma sputtering (SPS) process. We utilize the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in a liquid environment, (2) to endow biocompatibility to the AuNPs, and (3) to provide colloidal stability to the AuNPs-alginate aqueous suspensions. The alginate concentrations were varied as 0.2, 0.5, and 0.9 %w/v. The concentration-dependent effect on the particle size of AuNPs, the physical absorption property and the stability of the AuNPs-alginate suspensions were studied. Results indicate that preparation of chemical-free colloidal AuNPs-alginate aqueous suspension is successful by the SPS process. The obtained colloidal suspensions were stable and able to retain their strong plasmon absorption bands within a reasonable time period. As a consequence, this is a high-potential technique to produce AuNPs suspended in alginate aqueous solution appropriate for biomedical applications. © 2014 The Royal Society of Chemistry.

DOI： 10.1039/c3ra45029e

Solution plasma exfoliation of graphene flakes from graphite electrodes

Lee H., Bratescu M., Ueno T., Saito N.

RSC Advances Vol. 4 ( 93 ) page： 51758 - 51765 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Graphene flakes were successfully produced by a simple method named a solution plasma process. The plasma was generated between two carbon electrode tips which were immersed in distilled water. The production approach is a continuous energy accumulation induced by focusing of plasma streamers on the surface of electrodes. This focused energy produces thermal gradient zones where a proper energy level is produced. Concisely, the energy is enough to extract graphene layers from the graphite structure but not enough to break covalent C-C bonds within the graphene sheets. Optical emission spectroscopy results showed the decomposition of carbon from the graphite electrodes with different intensities for the carbon species. Transmission electron microscopy images confirmed the hexagonal honeycomb structure of the graphene flakes. Furthermore, broadening of the 2D band in the Raman spectra revealed that the graphene flakes were disordered multilayers. This journal is

DOI： 10.1039/c4ra03253e

Solution plasma synthesis process of tungsten carbide on N-doped carbon nanocomposite with enhanced catalytic ORR activity and durability

Kim D., Li O., Pootawang P., Saito N.

RSC Advances Vol. 4 ( 32 ) page： 16813 - 16819 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

In this study, the enhancement of ORR activity and durability by an N-doped carbon nanocomposite on tungsten carbide (WC) nanoparticles was reported. The nanocomposite of tungsten carbide on two different carbon matrices, pure carbon matrix (WC/C) and N-doped carbon matrix (WC/N-C), was at first prepared by a simple discharge process in the mixture of benzene/dodecane and pyrrole/dodecane. The nanoparticles of tungsten carbide were formed via the sputtering effect of tungsten electrodes during discharge. The results of TEM and XRD demonstrated that tungsten carbide nanoparticles with a mean size of 6 nm were evenly dispersed on both carbon matrices. The results of cyclic voltammetry measurements showed that both obtained metal/carbon matrices promoted a significant oxygen reduction reaction (ORR) in alkaline solution. The ORR potential of tungsten carbide/carbon matrix and nitrogen-doped carbon were -0.29 V and -0.36 V, respectively. The enhancement of ORR activity in WC/N-C was attributed to the combined catalytic effects of WC and N in the carbon matrix. Although the ORR activity of WC/N-C was still incomparable with commercial Pt/C, the durability of the catalyst was significant higher than that of Pt/C in a methanol environment. The catalyst did not exhibit an evident change of initial current after 4000 s. Therefore, the inexpensive N-doped WC/C nanocomposite might be a promising and highly durable catalytic material for cathodes in fuel cell applications. © 2014 the Partner Organisations.

DOI： 10.1039/c4ra02380c

Solution plasma synthesis of nitrogen-doped carbon nanoballs as effective metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Chiba S., Saito N., Ishizaki T.

Materials Research Society Symposium Proceedings Vol. 1641 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Nitrogen-doped carbons nanoballs were synthesized from an organic liquid precursor (a mixture of benzene and pyrazine) by solution plasma process. After synthesis, they were further annealed at 700 and 900 °C under N2 atmosphere. The nitrogen-doped carbon nanoballs before and after thermal annealing process exhibit a similar morphological feature, and their diameters are in the range between 20 and 40 nm. With higher annealing temperature, the graphitization of the nitrogen-doped carbon nanoballs increases. For the electrocatalytic activity in an alkaline solution, the limiting current density and onset potential for the ORR activity can be significantly improved for the samples after thermal annealing at 900 °C. We anticipate that solution plasma process will be a viable alternative way for synthesizing heteroatom-doped carbon electrocatalysts for broad application in the field of fuel cells, metal-air batteries, and supercapacitors. © 2014 Materials Research Society.

DOI： 10.1557/opl.2014.319

Charge doping of large-area graphene by gold-alloy nanoparticles

Bratescu M., Saito N.

Journal of Physical Chemistry C Vol. 117 ( 50 ) page： 26804 - 26810 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

We present a facile, one-step, and surfactant-free method for direct synthesis and loading of stable gold and gold-alloy nanoparticles (NPs) on large-area graphene using an electrical discharge in a liquid environment, termed solution plasma. We observed a charge doping of graphene by the gold NPs, which depends on the particles' chemical composition, even if the NPs contain a few percent of trivalent sp metals, such as indium (In) or gallium (Ga). Raman and electron energy loss spectroscopy (EELS) methods show that graphene is doped with electrons (n-type) in the case of gold NPs and with holes (p-type) in the case of gold-alloy NPs. The Raman band shift indicates that the amount of the transferred electrons from the gold NPs to graphene is -2 × 10 -4 electrons per unit cell. The gold-alloy NPs receive from graphene (2 and 4) × 10-5 electrons per unit cell if the gold NPs contain In and Ga, respectively. In the EELS spectra, the decrease in the intensity of the 1s-π* transition and the shift of the π* peak to higher energy confirm the depopulation of the antibonding states caused by the electron transfer from graphene to the gold-alloy NPs. © 2013 American Chemical Society.

DOI： 10.1021/jp409368c

Functionalization of multiwalled carbon nanotubes by solution plasma processing in ammonia aqueous solution and preparation of composite material with polyamide 6

Shirafuji T., Noguchi Y., Yamamoto T., Hieda J., Saito N., Takai O., Tsuchimoto A., Nojima K., Okabe Y.

Japanese Journal of Applied Physics Vol. 52 ( 12 ) 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Solution plasma processing (SPP) has been performed on multiwalled carbon nanotubes (MWCNTs) in ammonia aqueous solution. The MWCNTs, which do not disperse in aqueous solution, uniformly dispersed after the SPP. Only 2 h was required to obtain 10 g of the dispersed MWCNTs, while 7 days and additional chemicals were required for 185mg in a previous study. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the SPP-treated MWCNTs revealed that nitrogen- and oxygen-containing groups are formed on the MWCNTs. Serious damage to the MWCNT structure was not observed in the Raman spectrum or transmission electron microscopy images of the SPP-treated MWCNTs. The composite materials prepared using polyamide 6 with the SPP-treated MWCNTs showed better tensile, bending, and impact strength than those prepared with nontreated MWCNTs. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.125101

Gold nanoparticle synthesis using three-dimensionally integrated micro-solution plasmas

Shirafuji T., Ueda J., Nakamura A., Cho S.P., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 52 ( 12 ) 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Three-dimensionally integrated micro-solution plasmas (3D IMSPs), in which microplasmas are generated in gas bubbles in an aqueous solution held in a porous dielectric material, have been applied to gold nanoparticle synthesis. Conventional solution plasma processes require additional chemicals to increase the electrical conductivity of the aqueous solution for generating plasmas. In contrast to this, 3D IMSPs have been found to generate plasmas without such a procedure when the aqueous solution has a low electrical conductivity as in the case of HAuCl4 for gold nanoparticle synthesis. The gold nanoparticle synthesis has been confirmed through the observation of optical absorption due to the plasmon resonance at 550 nm, and also through the characterization of their size, crystallinity, and composition by transmission electron microscopy and energy dispersive X-ray spectroscopy. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.126202

Degradation of β-chitosan by solution plasma process (SPP)

Prasertsung I., Damrongsakkul S., Saito N.

Polymer Degradation and Stability Vol. 98 ( 10 ) page： 2089 - 2093 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

In this work, the solution plasma process (SPP) is used to treat β-chitosan solutions in order to induce the degradation of chitosan. The effects of solution plasma on the properties of chitosan solutions are investigated. The treatment time was varied from 0 to 300 min. The plasma-treated chitosan was characterized by the following methods; molecular weight by GPC, viscosity, crystal structure by XRD, chemical characteristics by FT-IR, solubility by UV-vis spectrophotometer, and fractional analysis. The results showed that after treatment with plasma for 15-120 min, the viscosity of the chitosan solution and apparent molecular weight of chitosans decreased remarkably, when compared to those of untreated sample. Longer treatment times had less effect on both viscosity and molecular weight of the samples. This suggested that the degradation process of chitosan occurred during plasma treatment. The XRD analysis showed that the crystallinity of chitosan was destroyed, resulting in amorphous structure. FT-IR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. The %yield of water-soluble chitosan was increased with increasing plasma treatment time. These results implied that solution plasma process is able to induce the degradation of chitosan solutions. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.07.001

Highly efficient treatment of industrial wastewater by solution plasma with low environmental load

Cai L., Wu Y., Wu Y., Yamauti S., Saito N.

Water Science and Technology Vol. 68 ( 4 ) page： 923 - 928 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Water Science and Technology

Advanced oxidation techniques are efficient processes to dispose of organic contaminants in industrial wastewater with low secondary pollution. The solution plasma technique was featured as an advanced oxidation technique with low secondary pollution and high efficiency. However, the solution plasma technique reported previously could only treat wastewater of less than 200 mL owing to the limited plasma generated by only one pair of electrodes. In this work, multiple pairs of electrodes were installed at the bottom of the reaction vessel to generate plasma for decomposing methylene blue trihydrate (MB) and methyl orange (MO) solutions with a batch amount of 18 L/batch. The solution plasma technique was compared with direct ozonation in decomposition of MB and MO wastewater. A surprising phenomenon is that MO was more readily decomposed than MB by using direct ozonation, whereas the removal of MO was too low, and MB was more readily decomposed than MO by using the solution plasma technique. © IWA Publishing 2013.

DOI： 10.2166/wst.2013.321

Epitaxial growth of (111)-oriented BaTiO<inf>3</inf>/SrTiO<inf>3</inf> perovskite superlattices on Pt(111)/Ti/Al<inf>2</inf>O<inf>3</inf>(0001) substrates

Panomsuwan G., Takai O., Saito N.

Applied Physics Letters Vol. 103 ( 11 ) 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λ = 4.8 - 48 nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4820780

Generation of three-dimensionally integrated micro solution plasmas and its application to decomposition of organic contaminants in water

Shirafuji T., Himeno Y., Saito N., Takai O.

Journal of Photopolymer Science and Technology Vol. 26 ( 4 ) page： 507 - 511 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Photopolymer Science and Technology

Three-dimensionally integrated micro solution plasmas were generated in gas bubbles in porous dielectric materials filled with gas/liquid mixed medium. The methylene blue molecules in aqueous solution were decomposed by the treatment with the three-dimensionally integrated micro solution plasmas. Decomposition efficiency was 16 times higher than conventional solution plasma in the case of applied voltage of 5 kV. With decreasing applied voltage from 5 to 2 kV, the decomposition efficiency was improved up to 360% in comparison to that of 5 kV, while reduction in the decomposition rate was 40%. © 2013 SPST.

DOI： 10.2494/photopolymer.26.507

Solution plasma synthesis process of carbon nano particles in organic solutions

Li H., Kang J., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 7 ( 1 ) page： 31 - 36 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

In this study, solution plasma process (SPP) was applied to synthesis carbon nanoparticles in organic solution. In the SPP process, carbon nanoparticles were formed by carbon atoms supplied by two different groups of organic solutions, sugar and aromatic hydrocarbon solutions. Glucose, sucrose and fructose were used as sugar solution, whereas benzene and toluene were applied for the aromatic hydrocarbon solutions. Within the same group of solution, the carbon structure and size distribution were found to be similar. On average, 100 ml sugar solution produced 15 mg of carbon by weight. The particles included hemisphere and sphere in shape, with a size distribution between 100 - 600 nm. For aromatic hydrocarbon solutions, 930 and 1000 mg of carbon could be generated, respectively, from 100 ml of pure toluene and benzene. The particles were spherical shape with a size distribution of 20 - 30 nm. Fundamental characteristics of plasma discharge including voltage and current waveforms, as well as active species generated were compared. The discharge in sugar solution occurred in three different phases: pre-discharge, the initiation and the formation of discharge, whereas the discharge in benzene happened in two main steps: pre-discharging and the formation of discharge. From the optical emission spectrum, the major active species obtained from sugar solution were Hα (656 nm), followed by atomic O (777 nm), Hβ (486 nm) and relatively low intensity of atomic C (247 nm). For benzene and toluene solutions, the majority active species were observed to be C2 (513 nm) and CH (431 nm) and followed by Hα (656 nm). The results indicated pure benzene might be suitable solution applied for the synthesis of carbon nanoparticles in solution plasma process.

Crosslinking of a gelatin solutions induced by pulsed electrical discharges in solutions

Prasertsung I., Damrongsakkul S., Saito N.

Plasma Processes and Polymers Vol. 10 ( 9 ) page： 792 - 797 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Processes and Polymers

This study uses discharges in solutions for the treatment of gelatin solutions in order to generate crosslinking. The effects of plasma on the properties of gelatin solutions were investigated, the latter including viscosity, amino acid contents, chemical analyses, and gel strengths. The results show that, after short duration plasma treatments (5-10 min), the viscosity of the gelatin solutions increased, while the concentration of OH · free radicals decreased. After adding ethanol to the gelatin solutions, a greater increase in viscosity, and a greater decrease in free radicals were found. This suggests that ethanol provides more free radicals that can promote the crosslinking of the gelatin solution during the plasma treatment, resulting in higher viscosity. The gel strength of the gelatin was greatly enhanced by the plasma treatment of the solution. The results regarding the free amino acid contents showed that the crosslinking degree of plasma-treated gelatin was higher than that of the untreated gelatin. FTIR measurements show that after plasma treatment, the IR bands at 1 668 and 1 558 cm-1, corresponding to the amide I and II groups of gelatin, shifted to higher wavenumbers, i.e. 1 672 and 1 564 cm-1, respectively. This suggests that crosslinking has occurred between gelatin molecules. The results show that discharges in solutions may be able to induce crosslinking reactions in the gelatin. Electrical discharges in solutions can be chemical-free, alternative crosslinking methods. Electrical discharges are investigated for the treatment of gelatin solutions as potential crosslinking, non-toxic methods. Plasmas were found to induce crosslinking of gelatin molecules, as demonstrated by the increased viscosity, decreased free amino contents, and increased gel strength. The addition of ethanol in gelatin solutions enhanced the crosslinking; this is because ethanol provides more free radicals necessary for crosslinking reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/ppap.201200148

Synthesis of structure-controlled carbon nano spheres by solution plasma process

Kang J., Li O., Saito N.

Carbon Vol. 60 page： 292 - 298 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Structure-controlled carbon nanospheres (CNSs) were synthesized by an innovative plasma in liquid method, termed solution plasma processing (SPP). CNSs were formed by using benzene as a carbon precursor. Typically, 500 mg of CNSs were obtained from 100 ml of benzene with 20 min of treatment. The average diameters of CNSs increased from 20 to 100 nm when the pulse frequency of the bipolar power supply adjusted from 25 to 65 kHz. The TEM images showed that CNSs synthesized at 25-50 kHz consisted of amorphous carbon, while CNSs generated at 65 kHz were composed of continuous short range graphite with turbostratic structure. X-ray diffraction (XRD) patterns and TEM images showed that CNSs synthesized at 25-50 kHz had a low graphitization degree, while CNSs synthesized at 65 kHz consisted of graphite sheets with regular and ordering structure in basal planes. The increase of D/G intensity ratio in Raman spectroscopy confirmed the transition from amorphous carbon to nanocrystalline-graphite (NCG) with increasing pulse frequency. The resistivity of CNSs also increased with increasing pulse frequency. CNSs synthesized at 65 kHz have shown similar degree of resistivity as other commercial carbon black materials. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2013.04.040

A simple synthesis method for nano-metal catalyst supported on mesoporous carbon: The solution plasma process

Kang J., Li O., Saito N.

Nanoscale Vol. 5 ( 15 ) page： 6874 - 6882 2013.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanoscale

High-electrocatalytic-activity noble nanoparticles (NPs) supported on carbon nanoballs (CNBs) were synthesized using an innovative plasma-in-liquid method, which is known as solution plasma processing (SPP). This technique uses a one-step method for the synthesis of NPs on carbon materials. CNBs are formed using benzene as a carbon precursor while gold (Au) or platinum (Pt) nanoparticles are generated instantaneously via sputtering from metal electrodes. The synthesized NP/CNBs were annealed at 850 °C in order to increase the conductivity of the material. The results of structural characterizations reveal that the Au and Pt NPs are smaller than 10 nm and have a uniform size distribution, and these NPs are successfully loaded onto highly mesoporous CNBs that have an average pore diameter between 13 and 16 nm. In the results from cyclic voltammetry measurements, the Au/CNBs and Pt/CNBs show clear peaks corresponding to the oxidation and reduction features in the catalytic reactions. Apart from noble nanoparticles, SPP can also be used to synthesize various kinds of NPs including bimetallic NPs loaded on spherical carbon supports by changing the working electrodes. The proposed mechanism for the synthesis is discussed in detail. This method shows potential to be a candidate for the next-generation synthesis of NP/carbon in the future. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3nr01229h

One-step synthesis of gold bimetallic nanoparticles with various metal-compositions

Bratescu M., Takai O., Saito N.

Journal of Alloys and Compounds Vol. 562 page： 74 - 83 2013.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

A rapid, one-step process for the synthesis of bimetallic nanoparticles by simultaneous metal reduction and gold erosion in an aqueous solution discharge was investigated. Gold bimetallic nanoparticles were obtained by alloying gold with various types of metals belonging to one of the following categories: divalent sp metals, trivalent sp metals, 3d or 4d metals. The composition of the various gold bimetallic nanoparticles obtained depends on electrochemical factors, charge transfer between gold and other metal, and initial concentration of metal in solution. Transmission electron microscopy and energy dispersive spectroscopy show that the gold bimetallic nanoparticles were of mixed pattern, with sizes of between 5 and 20 nm. A red-shift of the surface plasmon resonance band in the case of the bimetallic nanoparticles Au-Fe, Au-Ga, and Au-In, and a blue-shift of the plasmon band of the Au-Ag nanoparticles was observed. In addition, the interaction of gold bimetallic nanoparticles with unpaired electrons, provided by a stable free radical molecule, was highest for those NPs obtained by alloying gold with a 3d metal. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2013.02.033

Effect of polymer concentration on the depolymerization of sodium alginate by the solution plasma process

Watthanaphanit A., Saito N.

Polymer Degradation and Stability Vol. 98 ( 5 ) page： 1072 - 1080 2013.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

Depolymerization of alginate was accessed, for the first time, by the plasma treatment in solution called solution plasma process (SPP). The process was done by applying an electrical discharge into a reactor containing sodium alginate aqueous solution. The key of the production is the generation of reactive species induced by the plasma in a liquid environment that can lead to the scission of polymer chains. Effect of polymer concentration on the SPP processing parameters and the depolymerization efficiency were studied. Three concentrations of sodium alginate solutions, i.e., 0.2, 0.5, and 0.9 %w/v, were prepared. The results showed that increasing concentration of the alginate solution decreased the applied voltage required for the generation of plasma. Optical emission spectra demonstrated that the generation of reactive species was the highest at the lowest alginate concentration (i.e. 0.2 %w/v). Therefore, molecular weight reduction of this concentration after the SPP was more remarkable than the others. The most significant species required for the depolymerization of alginate was the reactive hydrogen species. Molecular weight distributions (MWD) of the obtained low molecular weight alginates (LMALGs) for all concentrations were narrow. Furthermore, reduction trends of molecular weight and viscosity of alginate with varying operation times indicated that the depolymerization of alginate in aqueous solution by the SPP was affected by the combined contribution of two factors: (1) the amount of reactive species generated during the process and (2) the degree of chain entanglement of the polymers. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.01.011

Solution plasma sputtering processes for the synthesis of PtAu/C catalysts for Li-Air batteries

Terashima C., Iwai Y., Cho S.P., Ueno T., Zettsu N., Saito N., Takai O.

International Journal of Electrochemical Science Vol. 8 ( 4 ) page： 5407 - 5420 2013.4

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Electrochemical Science

Clean, nanosized PtAu/C catalysts were fabricated, using a simple one-step synthesis technique that involved sputtering discharge in liquid, and did not require the use of chemical species such as surfactants and/or reductants. This solution plasma sputtering was driven by a pulsed power supply, and was performed on the discharge between Pt and Au targets in a liquid dispersion of carbon black. Fine PtAu nanoparticles with an average diameter of 5.7 nm were uniformly deposited on the carbon support. The production and composition of the PtAu nanoparticles could be controlled via changes in the sputtering conditions. The Au-rich Pt19Au81/C (atomic %) catalysts provided higher specific capacity, even in carbonate-based electrolyte Li-air batteries, reducing the amount of Li2CO3 that was deposited on the bare carbon. © 2013 by ESG.

Facile fabrication of PtAu alloy clusters using solution plasma sputtering and their electrocatalytic activity

Hu X., Shen X., Takai O., Saito N.

Journal of Alloys and Compounds Vol. 552 page： 351 - 355 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Well-crystallized PtAu alloy clusters of about 2.0 nm in mean diameter are successfully fabricated via a one-step route of solution plasma sputtering at atmospheric pressure. The solution plasma provides a novel reaction field with highly energetic state for the formation of PtAu alloy clusters. The synergetic effects of rapid energetic radicals' bombardment, atom vapor diffusion, plasma expansion and solution medium condensation resulted in the formation of PtAu alloy clusters with various relative atom amount ratios. PtAu alloy clusters are highly dispersive in water for a long time without any polymeric stabilizer. As-fabricated PtAu alloy clusters show well electrocatalytic activity. PtAu alloy clusters are easily collected and well re-dispersed in various organic solvents for various potential applications. And PtAu alloy clusters supported on carbon were successfully fabricated by a one-step route. These results imply that this novel process will have potential application in future in the design and mass production of various multifunctional metal and/or alloy clusters. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2012.08.033

Fabrication and characterization of epitaxial SrTiO <inf>3</inf>/Nb-doped SrTiO <inf>3</inf> superlattices by double ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Vacuum Vol. 89 ( 1 ) page： 35 - 39 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Vacuum

Epitaxial oxide superlattices (SLs) of SrTiO 3 (STO) and Nb-doped SrTiO 3(STNO) were fabricated on LaAlO 3 (LAO) (001) substrates by an ion beam sputter deposition (IBSD) system having double electron cyclotron resonance (ECR) ion guns. The [STO x/STNO y] 10 SLs were epitaxially grown at different stacking sequences (x = 6 nm, y = 1-6 nm) and maintained the periodicity z of 10. Structural properties and surface morphology are found to be strongly dependent on the STNO sublayer thickness (y). Highly strained SLs with two-dimensional growth mode is observed at smaller STNO sublayer thickness (y = 1 nm). With increasing to a critical thickness (y = 4 nm), the SLs are freely strained and transformed to three-dimensional growth mode. The results demonstrate that the double ECR-IBSD is a versatile technique for the growth of high-quality oxide SLs. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2012.08.011

Growth of highly (110)- and (111)-textured SrTiO<inf>3</inf> thin films on Pt(111)/α-Al<inf>2</inf>O<inf>3</inf>(0001) substrates by ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Solid State Communications Vol. 158 page： 65 - 69 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Solid State Communications

SrTiO3 (STO) thin films were directly grown on Pt(111)/α-Al2O3(0001) substrates without Ti buffer layer using electron cyclotron resonance ion beam sputter deposition. Highly (110)- and (111)-textured STO films were obtained at 600 and 750 °C, respectively. The structural, morphological and electrical properties of both textured films were studied and compared. From high-resolution X-ray diffraction data and in-plane pole figure analysis, highly (110)-textured STO film was found to contain three orientation variants related by a 120°in-plane rotation, while highly (111)-textured STO film had two orientation variants related by a 180°in-plane rotation. The presence of rod- and triangular-shaped grains was observed for the (110)- and (111)-textured film surfaces, respectively. Their grain orientations were also consistent with the structural analysis. The leakage current characteristics of Pt/STO/Pt capacitors were found to follow the Schottky emission and Poole-Frenkel conduction mechanisms. A larger dielectric constant of (111)-textured film (320 at 100 kHz) was obtained in comparison with that of (110)-textured film (238 at 100 kHz) due to the effect of biaxial in-plane tensile strain and larger grain size. © 2013 Elsevier Ltd.

DOI： 10.1016/j.ssc.2012.12.026

Nanomechanical properties of amorphous and polycrystalline SrTiO <inf>3</inf> transparent thin films prepared by ion beam sputtering

Panomsuwan G., Takai O., Saito N.

Journal of Materials Engineering and Performance Vol. 22 ( 3 ) page： 863 - 868 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Engineering and Performance

Transparent SrTiO3 thin films were deposited on glass substrates by ion beam sputtering at various substrate temperatures. The structural characteristic of the deposited films shows the transition from amorphous phase to polycrystalline phase at 600 C. The films exhibit a good transparency in the visible region (∼80-85%) and a relatively smooth surface. The calculated band gaps for amorphous and polycrystalline films were ∼4.20 and ∼3.84 eV, respectively. The refractive index of the films increases with increasing the substrate temperature, and the extinction coefficient of the films in the visible region is in the order of 10-3, indicating low optical loss. The nanomechanical properties of the films were investigated using nanoindentation technique. Young's modulus and hardness for all films are found to be increased with the increase of substrate temperature. © 2012 ASM International.

DOI： 10.1007/s11665-012-0320-2

Discharge time dependence of a solution plasma process for colloidal copper nanoparticle synthesis and particle characteristics

Pootawang P., Saito N., Lee S.Y.

Nanotechnology Vol. 24 ( 5 ) 2013.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

In this study, we investigate a new synthetic route, termed the solution plasma process, for the synthesis of colloidal copper nanoparticles (CuNPs) in the presence of an amide and acid capping agent. Gelatin and ascorbic acid were selected as the capping agents to protect the particles against coalescence and oxidation side reaction. Using a high voltage power supply, CuNPs were rapidly formed by 1 min after the discharge. The size and shape of the CuNPs were dependent on the discharge time and were clearly influenced by the effect of the capping agents under two characteristics of the discharge medium (pH and temperature). With a long discharge time, the CuNP size tended to decrease with the formation of anisotropic particle morphologies: spherical, cubic, hexagonal, triangular and rod-like shapes. The decrease in CuNP size as a function of discharge time could be explained by the dissolution of CuNPs in a lower pH solution. After 5 min discharge the capping agent evidently allowed the protection of the synthesized CuNPs against oxidation with the presence of anisotropic CuNP shapes. It is demonstrated that the CuNP shape could be tuned from spherical to anisotropic shapes without the undesirable oxidation by adjusting the discharge time of the solution plasma. These advantages are valuable for material engineering to design the properties of Cu-based nanoparticles for the desired applications. © 2013 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/24/5/055604

Optical and mechanical properties of transparent SrTiO<inf>3</inf> thin films deposited by ECR ion beam sputter deposition

Panomsuwan G., Takai O., Saito N.

Physica Status Solidi (A) Applications and Materials Science Vol. 210 ( 2 ) page： 311 - 319 2013.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

SrTiO3 (STO) thin films have been deposited on glass substrates by electron cyclotron resonance (ECR) ion beam sputter deposition at different substrate temperatures (100-600 °C). The structural characteristics of the deposited films show a transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit good transparency with an interference pattern in the visible region and a very smooth surface without cracks. The refractive index of the films increases with an increase of the substrate temperature, and their dispersion was analyzed by a single-oscillator model. The extinction coefficient of the films in the visible region is of the order of 10 -3-10-2. The estimated values of the direct and indirect bandgap energies for the polycrystalline STO film are 3.80 and 3.32 eV, respectively. Its density is almost identical to the bulk STO single crystal, which is relatively high in comparison with those prepared by other techniques. The mechanical stability of the films is also improved with an increase of substrate temperature. Young's modulus and hardness of the polycrystalline STO film are 194.1 ± 15.5 and 22.5 ± 2.0 GPa, respectively. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201228077

Simple synthesis of platinum nanoparticles by plasma sputtering in water

Hu X., Takai O., Saito N.

Japanese Journal of Applied Physics Vol. 52 ( 1 PART2 ) 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

We applied a novel method of plasma sputtering in water for simple and fast preparation of carbon-supported platinum nanoparticles at atmospheric pressure from platinum wire electrodes without using any stabilizers, chemical reductant, plasma-generating gas, or salt solution in an open system. Upon plasma sputtering, special waveforms of voltage and current were obtained using a pulsed power supply. The obtained emission spectra clarified that platinum atoms were formed in the plasma region from the electrode surface owing to bombardment of the surface by highly energetic electrons and radicals derived from plasma. Thus, carbon-supported 2 nm and highly dispersed platinum nanoparticles were successfully synthesized by this fast and simple plasma sputtering method. Highly crystallized platinum nanoparticles show good electrocatalytic activity. This plasma sputtering technique has shown a potential application to the synthesis of other metal nanoparticles. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.01AN05

Gold nanoparticles supported on SrTiO<inf>3</inf> by solution plasma sputter deposition for enhancing UV- and visible-light photocatalytic efficiency

Panomsuwan G., Zettsu N., Saito N.

Materials Research Society Symposium Proceedings Vol. 1509 page： 80 - 85 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Gold (Au) nanoparticles were synthesized and deposited on the perovskite SrTiO3 (STO) via a one-step solution plasma sputter deposition (SPSD) without any reducing reagents at ambient condition. Good dispersion of the Au nanoparticles deposited on the STO surface was clearly observed. The synthesized Au nanoparticles were well-crystallized with a spherical shape and preferably exhibited multiply twinned structure. An average diameter of Au nanoparicles was estimated to be 6.1 ± 1.4 nm by transmission electron microscopy. Enhanced photocatalytic activity was found for the Au-STO when compared to the pure STO, as investigated from the degradation of methylene blue solution under ultraviolet and visible light irradiation. The SPSD seems to be a rapid and facile approach to prepare the Au nanoparticles supported on the metal oxide for photocatalytic applications. © 2013 Materials Research Society.

DOI： 10.1557/opl.2013.729

The role of activated nitrogen species on double-folded screen nitriding process

Kim S., Lee J., Saito N., Takai O.

Journal of Physics: Conference Series Vol. 417 ( 1 ) 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics: Conference Series

As clean and energy saving surface hardening technology, plasma nitriding techniques have been evolved with object of higher performance in the last decades. Even though the diffusion of nitrogen inward to steel is occurred at the final step, solid diffusion from surface, energy transition from gas molecule of nitrogen to atomic or an activated state have many different steps depending on the plasma conditions, parameters and the design of each equipment. And this study made comparative on nitrogen sources transfer with conventional DC plasma nitriding and novel nitriding process using plasma diagnosis and metallurgical observation. With different vacuum pressure, gas ratio and new designed electrode (double-folded screen cathode electrode), it showed a different behavior of DC plasma nitriding including the nano-sized nitride on the outer surface of specimen due to nitrogen source of determining plasma species. In this study, plasma species was able to identify with optical emission spectroscopy (OES) studies. From these observations, we could understand better role of ions or neutral nitrogen species, like neutral nitrogen (N), N2+ and NHx radicals in plasma nitriding process with different parameters. And cutting layers of nitride specimen were showed the results due to a different species gas flow ratio or plasma conditions.

DOI： 10.1088/1742-6596/417/1/012023

Synthesis of gold nanoparticles by solution plasma sputtering in various solvents

Hu X., Takai O., Saito N.

Journal of Physics: Conference Series Vol. 417 ( 1 ) 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics: Conference Series

Gold clusters (average particle size is 1.5 nm) and nanoparticles (average particle size is 3.5 nm) with spherical morphology were fabricated by solution plasma sputtering in solution medium. This process was carried out in an open system under atmospheric pressure. During plasma region, rapid energetic radicals' bombardment, atom vapour diffusion, plasma expansion and medium condensation resulted in the formation of gold nanoparticles from its electrode wires. As-fabricated gold particles have well crystalline even for less than 1 nm cluster. Gold nanoparticles with average size about 3.5 nm gave obviously surface plasmon resonance band at near 511 nm. While surface plasmon resonance band was disappearing for 1.5 nm-cluster formed in liquid nitrogen.

DOI： 10.1088/1742-6596/417/1/012030

In situ preparation of gold nanoparticles in alginate gel matrix by solution plasma sputtering process

Watthanaphanit A., Panomsuwan G., Saito N.

Materials Research Society Symposium Proceedings Vol. 1569 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

The rapid synthesis of gold nanoparticles (AuNPs) was done by solution plasma sputtering (SPS) process in the presence of a biopolymer, sodium alginate. We utilized the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in liquid environment, (2) to provide colloidal stability, and (3) to render biocompatibility to the AuNPs. The effect of sodium alginate concentration (varied as 0.2, 0.5, and 0.9 %w/v) and plasma sputtering time on the particle size and the physical absorption property of the AuNPs were studied. The results indicated that preparation of AuNPs in alginate gel matrix was successful by the SPS process in one step without any reducing agents. This technique has high potential as a novel strategy to produce AuNPs suspended in alginate aqueous solution which is suitable for biomedical application. Copyright © Materials Research Society 2013.

DOI： 10.1557/opl.2013.766

Synthesis of Nanomaterials by Solution Plasma Processing

Takai, O; Bratescu, MA; Ueno, T; Saito, N

MICRO-NANO MECHATRONICS - NEW TRENDS IN MATERIAL, MEASUREMENT, CONTROL, MANUFACTURING AND THEIR APPLICATIONS IN BIOMEDICAL ENGINEERING page： 109 - 121 2013

Orientation control of textured SrTiO<inf>3</inf> thin films on platinized α-Al<inf>2</inf>O<inf>3</inf> (0 0 0 1) by an ion beam sputter deposition method

Panomsuwan G., Takai O., Saito N.

Journal of Physics D: Applied Physics Vol. 45 ( 49 ) 2012.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

SrTiO3 (STO) thin films were grown on Pt/Al2O 3 substrates without a Ti adhesion layer by an ion beam sputter deposition method in a range of growth temperatures between 600 and 750 °C. The effect of growth temperature on the film orientation was investigated by high-resolution x-ray diffraction, pole figure measurements and in-plane grazing incidence x-ray diffraction. The film orientation showed a strong dependence on the growth temperature. The films exhibited a predominant (1 1 0) orientation at a low growth temperature of 600 °C. With an increase in growth temperature to 750 °C, a highly (1 1 1)-textured STO film with two different orientation variants was achieved on the Pt/Al2O3 substrate. A narrow full-width at half-maximum of 0.12° for the rocking curve measured on 2 2 2 STO reflection and a six-fold symmetry from {1 0 0} STO and {1 1 0} STO pole figures were observed. Three-dimensional island growth mode was observed on the surfaces of all films, as investigated with an atomic force microscope. The evolution of grain shape and size was apparently found with an increase in growth temperature. The root-mean-square roughness of the STO film grown at 750 °C was raised to be about 4 nm due to the surface faceting of (1 1 1)-oriented grains. The growth mechanism of the (1 1 0)- and (1 1 1)-textured STO films on the Pt/Al2O3 substrates was also explained and discussed in detail. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/45/49/494003

Rapid sterilization of Escherichia coli by solution plasma process

Andreeva N., Ishizaki T., Baroch P., Saito N.

Japanese Journal of Applied Physics Vol. 51 ( 12 ) 2012.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Solution plasma (SP), which is a discharge in the liquid phase, has the potential for rapid sterilization of water without chemical agents. The discharge showed a strong sterilization performance against Escherichia coli bacteria. The decimal value (D value) of the reduction time for E. coli by this system with an electrode distance of 1.0mm was estimated to be approximately 1.0 min. Our discharge system in the liquid phase caused no physical damage to the E. coli and only a small increase in the temperature of the aqueous solution. The UV light generated by the discharge was an important factor in the sterilization of E. coli. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.126201

15th International conference on thin films (ICTF-15)

Takai O., Saito N., Terashima C.

Journal of the Vacuum Society of Japan Vol. 55 ( 10 ) page： 464 - 468 2012.11

Synthesis and characteristics of Ag/Pt bimetallic nanocomposites by arc-discharge solution plasma processing

Pootawang P., Saito N., Takai O., Lee S.Y.

Nanotechnology Vol. 23 ( 39 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

Arc discharge in solution, generated by applying a high voltage of unipolar pulsed dc to electrodes of Ag and Pt, was used as a method to form Ag/Pt bimetallic nanocomposites via electrode erosion by the effects of the electric arc at the cathode (Ag rod) and the sputtering at the anode (Pt rod). Ag/Pt bimetallic nanocomposites were formed as colloidal particles dispersed in solution via the reduction of hydrogen radicals generated during discharge without the addition of chemical precursor or reducing agent. At a discharge time of 30s, the fine bimetallic nanoparticles with a mean particle size of approximately 5nm were observed by transmission electron microscopy (TEM). With increasing discharge time, the bimetallic nanoparticle size tended to increase by forming an agglomeration. The presence of the relatively small amount of Pt dispersed in the Ag matrix could be observed by the analytical mapping mode of energy-dispersive x-ray spectroscopy and high-resolution TEM. This demonstrated that the synthesized particle was in the form of a nanocomposite. No contamination of other chemical substances was detected by x-ray photoelectron spectroscopy. Hence, solution plasma could be a clean and simple process to effectively synthesize Ag/Pt bimetallic nanocomposites and it is expected to be widely applicable in the preparation of several types of nanoparticle. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/23/39/395602

Rapid synthesis of ordered hexagonal mesoporous silica and their incorporation with Ag nanoparticles by solution plasma

Pootawang P., Saito N., Takai O., Lee S.Y.

Materials Research Bulletin Vol. 47 ( 10 ) page： 2726 - 2729 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Bulletin

Rapid synthesis of silica with ordered hexagonal mesopore arrangement was obtained using solution plasma process (SPP) by discharging the mixture of P123 triblock copolymer/TEOS in acid solution. SPP, moreover, was utilized for Ag nanoparticles (AgNPs) incorporation in silica framework as one-batch process using silver nitrate (AgNO 3) solution as precursor. The turbid silicate gel was clearly observed after discharge for 1 min and the white precipitate formed at 3 min. The mesopore with hexagonal arrangement and AgNPs were observed in mesoporous silica. Two regions of X-ray diffraction patterns (2θ < 2° and 2θ = 35-90°) corresponded to the mesoporous silica and Ag nanocrystal characteristics. Comparing with mesoporous silica prepared by a conventional sol-gel route, surface area and pore diameter of mesoporous silica prepared by solution plasma were observed to be larger. In addition, the increase in Ag loading resulted in the decrease in surface area with insignificant variation in the pore diameter of mesoporous silica. SPP could be successfully utilized not only to enhance gelation time but also to increase surface area and pore diameter of mesoporous silica. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.materresbull.2012.04.040

Enhanced memory window of Au/BaTiO <inf>3</inf>/SrTiO <inf>3</inf>/Si(001) MFIS structure with high c-axis orientation for non-volatile memory applications

Panomsuwan G., Takai O., Saito N.

Applied Physics A: Materials Science and Processing Vol. 108 ( 2 ) page： 337 - 342 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics A: Materials Science and Processing

Metal-ferroelectric-insulator-semiconductor (MFIS) structures with BaTiO 3 (BTO) as a ferroelectric film and SrTiO 3 (STO) as an insulating buffer layer were fabricated on p-type Si(001) substrates using an ion beam sputter deposition technique. The effect of out-of-plane orientation on the electrical properties of the MFIS structures, including leakage current density and memory window behavior, were studied using the growth of the BTO ferroelectric film on Si substrate buffered by highly c-axis-oriented and randomoriented STO buffer layers. The experimental results show that the out-of-plane orientations of the BTO films were almost identical to those of the STO buffer layers. The MFIS structure with a high c-axis orientation exhibited a maximum clockwise capacitance-voltage memory window of 1.17 V with a low leakage current of 1.05 × 10 -7 A/cm 2 at an applied voltage of 4 V, which is a significant improvement compared to the MFIS structure with a random orientation. The difference in the electrical properties of the MFIS structures with both types of orientation is discussed in detail. The results obtained from this study indicate that the Au/BTO/STO/p-Si MFIS structure with high c-axis orientation has good potential for use in non-volatile memory applications. © Springer-Verlag 2012.

DOI： 10.1007/s00339-012-7011-6

Treatment of non-point sources by a thermal plasma system under DC partial transferred mode

Li O.L., Guo Y., Chang J.S., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 6 ( 1 ) page： 63 - 67 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

Stormwater from urban areas is often accompanied with a variety of chemicals such as heavy metals, phosphorus, trace organic and hydrocarbons. Thermal plasma under DC transferred mode was proposed for decontamination of sediment carried by urban stormwater. After dredging, stormwater sediment/sludge accumulated in a stormwater detention pond was spread on top of a filter and the residues were transferred to a thermal plasma reactor. The reduction of total organic carbon (TOC) is 22% on average. Sediment was melted into slag with thermal plasma treatment under DC partial transferred operating mode. After treatment, the major compositions of the original stormwater sludge (e.g. sand (SiO 2) and calcite (CaCO 3)) decreased while other compositions such as KAlSi 3O 8, Fe 3O 4, NaCl and CaSO 4 were formed. The accumulated concentrations of C xH y, CO, CO 2, NO, NO 2, H 2S and SO 2 after a twohour thermal plasma treatment were 6100, 10000, 6200, 9700, 140, 40 and 27 ppm, respectively.

Study on the combustion inhibition of poly phenylene ether alloy

Yamashita T., Nakashima E., Takeda K., Saito N., Takai O.

Kobunshi Ronbunshu Vol. 69 ( 6 ) page： 297 - 299 2012.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Kobunshi Ronbunshu

In this study, we evaluated the flame retardant properties of several chemical compounds to polyphenylene ether alloy. Some of them (metallic sulfide and a variety of carboxylate salts) are stronger than general flame retardants such as red phosphorus. Molybdenum disulfide is widely used as lubricant and sodium benzoate and disodium succinate are used as food additives. So it is a new insight that they have a significant effect on the flame retardancy of polyphenylene ether alloy. Molybdenum disulfide is a catalyst that degrades polyphenylene ether alloy. We also found a combinatorial effect when blending polyphenylene ether alloy with both molybdenum disulfide and sodium benzoate that show a stronger combustion inhibition than each single compound. ©2012, The Society of Polymer Science, Japan.

DOI： 10.1295/koron.69.297

Preparation and wettability examinations of transparent SiO<inf>2</inf> binder-added MgF<inf>2</inf> nanoparticle coatings covered with fluoro-alkyl silane self-assembled monolayer

Murata T., Hieda J., Saito N., Takai O.

Applied Optics Vol. 51 ( 13 ) page： 2298 - 2305 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Optics

SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on fused silica-glass substrates from autoclaved sols prepared at 100-180 °C. To give it hydrophobicity, we treated the samples with fluoro-alkyl silane (FAS) vapor to form self-assembled monolayers on the nanoparticle coating and we examined the wettability of the samples. The samples preserved good transparency even after the FAS treatment. The wettability examination revealed that higher autoclave temperatures produced a larger average MgF2 nanoparticle particle size, a larger surface roughness, and a higher contact angle and the roll-off angle. © 2012 Optical Society of America.

DOI： 10.1364/AO.51.002298

Active species generated by a pulsed arc electrohydraulic discharge plasma channel in contaminated water treatments

Li O.L., Takeuchi N., He Z., Guo Y., Yasuoka K., Chang J.S., Saito N.

Plasma Chemistry and Plasma Processing Vol. 32 ( 2 ) page： 343 - 358 2012.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Chemistry and Plasma Processing

Pulsed arc electrohydraulic discharge (PAED) direct plasma technique was applied for various types of contaminated water treatment. The experimental system consists of a spark-gap switch type pulse power supply (0.5 kJ/pulse) and a 3 L stainless steel reactor with eccentrically configured rod-to-rod electrodes. The current and voltage waveforms are fundamentally different for different conductivity water. Double pulse current discharges were observed for pond water with relatively higher conductivity (637 mS/m) while a single pulse current discharge was observed for lake water with relatively lower conductivity (78 mS/m). From the optical emission spectrum and UV dosimeters, UV-A, UV-B, excited molecules and radicals including N 2*, O, H, OH, O3 etc. were observed during the discharge period. Both optical emission and UV intensities in pond water are slightly lower than lake water. The decay time of the UV-A, N 2*, OH, H and O radicals were around 0.6 ms, where the discharge period ended around 0.4 ms. The results indicate that the radicals existed longer than the discharge period. The pH, dissolved oxygen and conductivity were changed during the course of PAED treatment. The ions and radicals such as H·, O·, H +, OH· etc. generated by PAED may cause alterations density decay time and the active species in water were present for a longer period. The reduction of total organic carbon (TOC) in pond water reached 80% after 5 min of PAED treatment Based on local thermal plasma equilibrium (LTE) model, LTE thermal plasma chemical composition model for 1 mol water vapour was used to compare to present experiments. PAED discharge in contaminated pond water generated peak concentration of OH = 28% and O 2H = 0.012% mol in gas-phase and migrated to water-phase via gas-liquid interfaces generated by arc and micro-bubbles to form more stable O3, H2O 2, H2 and O 2. The model suggested that the reduction of TOC occurred in gas/plasma phases or liquid-phase side of gas liquid interfaces. © Springer Science+Business Media, LLC 2011.

DOI： 10.1007/s11090-011-9346-8

High sensitive detection of volatile organic compounds using superhydrophobic quartz crystal microbalance

Andreeva N., Ishizaki T., Baroch P., Saito N.

Sensors and Actuators, B: Chemical Vol. 164 ( 1 ) page： 15 - 21 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical

A quartz crystal microbalance (QCM) chemical sensor coated with superhydrophobic film for detecting volatile organic compounds (VOCs) such as formaldehyde and toluene under ambient conditions was developed. The superhydrophobic film was deposited by means of microwave plasma enhanced chemical vapor deposition (MPECVD). The sensitivities of QCM sensor coated with superhydrophobic film to VOCs such as formaldehyde and toluene were investigated under ambient conditions. The sensitivity of the sensor to formaldehyde and toluene was considerably improved by the superhydrophobic surface modification. The surface modification promoted microscopic texturing to the film surface and thus increased the effective specific surface area of the sensor for the adsorption of formaldehyde and toluene. In addition, the adsorption of water molecules was minimized due to the superhydrophobic film deposited on the sensor surface, thus promoting the preferential adsorption of formaldehyde and toluene molecules on the QCM sensor coated with superhydrophobic film, compared to the conventional QCM sensor. Moreover, the adsorption mechanisms of formaldehyde-water and toluene-water molecules to the superhydrophobic film were discussed. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2012.01.051

Preparation of low molecular weight chitosan using solution plasma system

Prasertsung I., Damrongsakkul S., Terashima C., Saito N., Takai O.

Carbohydrate Polymers Vol. 87 ( 4 ) page： 2745 - 2749 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

The solution plasma system was introduced to treat chitosan solution in order to prepare low molecular weight chitosan. The plasma treatment time was varied from 0 min to 300 min. The plasma-treated chitosan was characterized including viscosity, molecular weight by GPC, and chemical characteristics by FT-IR. The results showed that after treated with plasma for 15-60 min, the viscosity of chitosan solution and apparent molecular weight of chitosans were remarkably decreased, compared to those of untreated sample. Longer treatment time had less effect on both viscosity and molecular weight of samples. Eventually, long treatment time (>180 min) showed no influence on both viscosity and apparent molecular weight. This suggested that the degradation process of chitosan occurred during plasma treatment. FTIR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. TOF-MS results showed that chitooligosaccharides with the degree of polymerization of 2-8 were also generated by solution plasma treatment. The results suggested that solution plasma system could be a potential method for the preparation of low molecular weight chitosan and chitooligosaccharides. © 2011 Elsevier Ltd.

DOI： 10.1016/j.carbpol.2011.11.055

Growth and characterization of highly c-axis textured SrTiO <inf>3</inf> thin films directly grown on Si(001) substrates by ion beam sputter deposition

Panomsuwan G., Cho S., Saito N., Takai O.

Crystal Research and Technology Vol. 47 ( 2 ) page： 187 - 194 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystal Research and Technology

Highly c-axis textured SrTiO 3 (STO) thin films have been directly grown on Si(001) substrates using ion beam sputter deposition technique without any buffer layer. The substrate temperature was varied, while other parameters were fixed in order to study effect of substrate temperature on morphology and texture evolution of STO films. X-ray diffraction, pole figure analysis, atomic force microscope, and high-resolution electron microscopy were used to characterize and confirm quality and texture of the STO films. The experimental results show that optimum substrate temperature to achieve highly c-axis textured films is at 700 °C. The full width at half maximum (FWHM) of 002 STO was found to be 2° and fraction of (011) orientation was as low as 1%. The surface morphology was Volmer-Weber growth mode with a small roughness ∼1 nm. The lowest leakage current density (5.8 μA/cm 2 at 2 V) and the highest dielectric constant (Îμ STO ∼ 98) were found for highly c-axis textured films grown at 700 °C. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/crat.201100573

Rapid synthesis and structural characterization of well-defined gold clusters by solution plasma sputtering

Hu X., Cho S., Takai O., Saito N.

Crystal Growth and Design Vol. 12 ( 1 ) page： 119 - 123 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystal Growth and Design

Ultrafine metal nanoparticles of a few nanometers in diameter exhibit size-dependent photonic and electric properties that are of interest for applications such as biosensors, catalysts, optics, and electronics. Chemical approaches and vacuum metal-vapor-condensation physical techniques were used to successfully synthesize gold nanoparticles. While it is difficult to obtain monodisperse and small sized gold nanoparticles without any reductant and polymer stabilizer or under vacuum conditions, in the present study, multiply twinned and near monodisperse gold clusters of diameter less than 2.0 nm were successfully fabricated for the first time by solution plasma sputtering in liquid nitrogen (LN 2) without any chemical additions (such as reductant and polymer stabilizer). Gold clusters formed in several microseconds simultaneously with solution plasma sputtering in an open system under atmospheric pressure. Gold clusters are identified to be well crystalline and multitwin-particles (MTPs) by high-resolution transmission electron microscopy. No surface plasmon resonance band was detected in the gold cluster aqueous solutions. Such MTPs with special corners and edges would be beneficial for tailoring catalytic properties at the nanoscale. The solution plasma sputtering method will have potential application in the future in the design and mass preparation of various multifunctional metal clusters. © 2011 American Chemical Society.

DOI： 10.1021/cg2008528

Effect of Sn<sup>4+</sup> additives on the microstructure and corrosion resistance of anodic coating formed on AZ31 magnesium alloy in alkaline solution

Salman S.A., Kuroda K., Saito N., Okido M.

Magnesium Technology page： 241 - 245 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：Magnesium Technology

Magnesium is the lightest structural metal with high specific strength and good mechanical properties. However, poor corrosion resistance limits its widespread use in many applications. Magnesium is usually treated with chromate conversion coatings. However, due to changing environmental regulations and pollution prevention requirements, a significant push exists to find new, alternative for poisonous Cr6+. Therefore, we aim to improve corrosion resistance of anodic coatings on AZ31 alloys using low cost non-chromate electrolyte. Anodizing was carried out in alkaline solutions with tin additives. The effect of tin additives on the coating film was characterized by SEM and XRD. The corrosion resistance was evaluated using anodic and cathodic polarizations and electrochemical impedance spectroscopy (EIS). Corrosion resistance property was improved with tin additives and the best anti-corrosion property was obtained with addition of 0.03 M Na 2SnO3.3H2O to anodizing solution.

DOI： 10.1002/9781118359228.ch45

Size-controlled gold nanoparticles synthesized in solution plasma

Bratescu M.A., Cho S.P., Takai O., Saito N.

Journal of Physical Chemistry C Vol. 115 ( 50 ) page： 24569 - 24576 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Size-controlled gold nanoparticles (NPs) have been synthesized using an electrical discharge in a liquid environment, termed solution plasma processing (SPP). The gold NPs exhibit sizes from 1 to 2 to 10 nm when the solution pH was adjusted in the range from 12 to 3, respectively. The chemical environment surrounding the gold NPs depends on the preparation conditions and determines the electrostatic interaction among the nanoparticles, which alters their final size. Information obtained from XPS analysis, ToF-SIMS mass spectra, and UV-vis absorption spectroscopy were consistent and demonstrate that the gold NPs are partially oxidized on the surface, when synthesized in a pH 12 solution, and remain surrounded by gold chloride compounds when synthesized in a pH 3 solution. Plasma diagnostics shows that a high electron density contributes to generating a larger number of hydrogen radicals, which represent the main component in the reduction process of the gold ion into the neutral form. © 2011 American Chemical Society.

DOI： 10.1021/jp207447c

Low-temperature fabrication of bunch-shaped ZnO nanowires using a sodium hydroxide aqueous solution

Hu X., Masuda Y., Ohji T., Saito N., Kato K.

Journal of Nanoscience and Nanotechnology Vol. 11 ( 12 ) page： 10935 - 10939 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology

Bunch-shaped ZnO nanowires film was successfully fabricated by the forced-hydrolysis-initiatednucleation of anhydrous zinc acetate in an aqueous solution of zinc acetate and sodium hydroxide at low temperature. X-ray diffraction and a field emission scanning electron microscope clarified their formation mechanism and morphology development. The morphology was controllable by adjusting the solution temperature and deposition time. ZnO nanowires obtained at 65 °C for 6 h have a high aspect ratio of about 106. The smaller diameter with higher aspect ratio of ZnO nanowires, the easier the formation of bunch shapes by the capillary force during the drying process. This fabrication technique indicated that bunched ZnO film was prepared at low cost, and fittable to low heat-resistance substrates such as a polymer substarte. Copyright © 2011 American Scientific Publishers All rights reserved.

DOI： 10.1166/jnn.2011.4045

Cell adhesion behaviors on polyethylene terephthalate surface modified by surface-wave plasma-initiated graft polymerization

Ishizaki T., Andreeva N., Saito N.

Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011 Vol. 1 page： 437 - 440 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011

Hydrophilic modification of polyethylene terephthalate (PET) was successfully achieved by surface wave plasma treatment followed by graft polymerization with acrylic acid (AA) monomer. The graft reaction was confirmed by water contact angle measurements and X-ray photoelectron spectroscopy (XPS). 3T3 fibroblast cells were cultured on the AA-modified PET surface. The protein adsorption behaviors were also investigated using an optical waveguide spectroscopy.

Microstructural characterization of gold nanoparticles synthesized by solution plasma processing

Cho S., Bratescu M., Saito N., Takai O.

Nanotechnology Vol. 22 ( 45 ) 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

Microstructural characteristics of gold nanoparticles (Au NPs) fabricated by solution plasma processing (SPP) in reverse micelle solutions have been studied by high-resolution transmission electron microscopy (HRTEM). The synthesized Au NPs, with an average size of 6.3 1.4nm, have different crystal characteristics; fcc single-crystalline particles, multiply twinned particles (MTPs), and incomplete MTPs (single-nanotwinned fcc configuration). The crystal structure characteristics of the Au NPs synthesized by the SPP method were analyzed and compared with similar-size Au NPs obtained by the conventional chemical reduction synthesis (CRS) method. The TEM analysis results show that the Au NPs synthesized by the CRS method have shapes and crystal structures similar to those nanoparticles obtained by the SPP method. However, from the detailed HRTEM analysis, the relative number of the Au MTPs and incomplete MTPs to the total number of the Au NPs synthesized by the SPP method was observed to be around 94%, whereas the relative number of these kinds of crystal structures fabricated by the CRS method was about 63%. It is most likely that the enhanced formation of the Au MTPs is due to the fact that the SPP method generates highly reaction-activated species under low environmental temperature conditions. © 2011 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/22/45/455701

Wettability characterization of transparent MgF<inf>2</inf> nanoparticle coatings with SiO<inf>2</inf> binder covered with fluoroalkylsilane self-assembled monolayers

Murata T., Hieda J., Saito N., Takai O.

Journal of Sol-Gel Science and Technology Vol. 60 ( 2 ) page： 125 - 130 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Sol-Gel Science and Technology

SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on silica-glass substrates from autoclaved sols prepared at 100-180 °C. The samples were exposed to fluoro-alkyl silane (FAS) vapor to give hydrophobicity. All nanoparticle samples before FAS treatment had transmittances higher than 93% and such values were preserved even after FAS treatment. We examined root mean square roughnesses of the nanoparticle coatings with a Scanning Probe Microscope. We also examined their static and dynamic wettabilities with a contact angle meter and calculated their adhesive energies and surface free energies (SFEs). The surface roughness of the nanoparticle coating increased with the increase of the autoclave temperature. In addition, higher autoclave temperature caused increases in the sliding angle and decreases in the SFE. Interestingly, the higher the contact angle was, the larger the sliding angle was, although smaller sliding angle was expected with a larger contact angle. © 2011 Springer Science+Business Media, LLC.

DOI： 10.1007/s10971-011-2566-9

Effect of the electrode work function on the water plasma breakdown voltage

Miron C., Bratescu M., Saito N., Takai O.

Current Applied Physics Vol. 11 ( 5 SUPPL. ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Current Applied Physics

Experimental studies on the plasma initiated in ultrapure water between pairs of tungsten and lanthanum hexaboride electrodes have been performed. The current - voltage characteristics showed the features of a spark discharge for the both types of electrodes used in the process. The breakdown voltage depended on the work function and on the surface morphology of the electrodes. The reactive species formed in the water plasma and their emission intensity depended on the electrode material. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cap.2011.04.005

Redox reactions in liquid plasma during iron oxide and oxide-hydroxide nanoparticles synthesis

Bratescu M., Saito N., Takai O.

Current Applied Physics Vol. 11 ( 5 SUPPL. ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Current Applied Physics

A new synthesis method of iron oxide and iron oxide-hydroxide nanoparticles by pulsed liquid plasma process is presented. The redox reaction rates in liquid phase depend on the relative number densities of oxygen and hydrogen atoms produced in plasma gas phase and on the injected energy per pulse. The oxidation rate was higher than the reduction one in both regimes of plasma operation as glow and arc discharge. An oxidation rate of 0.13 μg mL -1 s-1 and a reduction rate of 0.04 μg mL-1 s-1 of iron ion during the process were obtained when plasma operates in glow discharge regime. The α-Fe2O3 and β-FeO(OH) nanoparticles of 80 nm size with a rice-shape morphology can be rapidly synthesized using low energy injected in plasma. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cap.2011.06.007

Adhesion property of SiO<inf>x</inf>-doped Diamond-like Carbon Films Deposited on Polycarbonate by Inductively Coupled Plasma Chemical Vapor Deposition

Baek S.M., Shirafuji T., Saito N., Takai O.

Thin Solid Films Vol. 519 ( 20 ) page： 6678 - 6682 2011.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

SiOx-DLC (diamond-like coating) films as candidates for protection coating of polymers were prepared by using a pulse-biased inductively coupled plasma chemical vapor deposition system with acetylene, tetramethylsilane and oxygen gasses. Effects of the gas composition and O 2 plasma pre-treatment on adhesion of the SiOx-DLC films were investigated. Adhesion strength of Si-DLC films (with 0% oxygen) was almost the same to that of undoped DLC films. By employing O2-plasma pre-treatment, adhesion strength of the Si-DLC films was considerably improved, while that of the undoped DLC films was not. The SiOx-DLC films with the carbon to oxygen (O/C) ratio of 0.15 showed adhesion strength as high as that of the Si-DLC films on the O2-plasma pre-treated substrate. However, further improvement of adhesion strength of the SiOx-DLC was not realized by employing the O2-plasma pre-treatment. On the other hand, the SiOx-DLC films showed favorable feature of high deposition rate and large optical band gap although higher O/C ratio (> 0.15) brought about poor adhesion strength of the films. © 2011 Elsevier B.V.

DOI： 10.1016/j.tsf.2011.04.080

Solution plasma for template removal in mesoporous silica: PH and discharge time varying characteristics

Pootawang P., Saito N., Takai O.

Thin Solid Films Vol. 519 ( 20 ) page： 7030 - 7035 2011.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

The evaluation of the ability of solution plasma process, SPP, depending on the pH of the discharge solution and discharge time for template removal in mesoporous silica was described. In the synthesis of mesoporous silica, ternary surfactant system containing tri-block copolymer EO20PO 69EO20 (P123), sodium dodecylbenzene sulfonate (SDBS), and 1,1,2,2,3,3,4,4,4-nonafluoro-1-butyl sulfonate (NFBS) was chemically used for synthesis under acid condition via sol-gel method then SPP was employed for template removal. The ordered 2D hexagonal arrangement was observed by the evidence of high resolution TEM and the diffraction mode of X-ray. The efficiency of SPP depending on the pH of the discharge solution and discharge time was scientifically demonstrated as a function of BET surface area. In the case of pH dependence, it was achieved that the ability of template removal in acid and base solutions was clearly higher than those of such results in neutral solution. In the term of discharge time, moreover, the percentage of template removal comparing in the result of BET surface area increased as the increase in discharge time. © 2011 Elsevier B.V.

DOI： 10.1016/j.tsf.2011.01.213

Fabrication of transparent protective diamond-like carbon films on polymer

Baek S.M., Shirafuji T., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 50 ( 8 PART 2 ) 2011.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Si doped hydrogenated amorphous carbon (Si-DLC) films as a candidate protection coating for polycarbonate (PC) were prepared using a pulsebiased inductively coupled plasma chemical vapor deposition (ICP-CVD) system with a gas mixture of acetylene (C2H2) and tetramethylsilane [Si(CH3)4]. The effects of Si incorporation on the structure and optical properties of the Si-DLC films were investigated. In addition, plasma pretreatments with O2, N2, and Ar gases were carried out to enhance the adhesion strength of Si-DLC films on polycarbonate. Structural characterization through Raman and X-ray photoelectron spectroscopy (XPS) analyses showed that the incorporation of Si atoms in DLC films leads to an increase in the optical band gap (Eopt) with the formation of sp3 C-Si bonds. O2 plasma pretreatment improved the strength of adhesion of the Si-DLC films to polycarbonate, while Ar and N2 plasma treatments did not. This can be explained by the formation of an activated dense interfacial layer by O2 plasma pretreatment. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.08JD08

Wettability of MgF<inf>2</inf> porous nanoparticle layers covered with fluoroalkylsilane self-assembled monolayer

Murata T., Hieda J., Saito N., Takai O.

Journal of the Ceramic Society of Japan Vol. 119 ( 1391 ) page： 591 - 594 2011.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Ceramic Society of Japan

MgF2 porous nanoparticle coatings with SiO2 binder were formed on glasssubstrates by solgel method. The samples were exposed to fluoro-alkyl silane (FAS) vapor and heated at 150°C to give water repellency. We measured surface roughnesses and static contact angles of water of the samples and examined the relation between surface roughnesses and contact angles. Scanning Probe Microscopy (SPM) confirmed that the FAS treatment had no effect on the surfaceroughness. In the autoclave temperature region of 100180° C, the higher the autoclave temperaturewas, the larger the surface roughness was. The sample prepared from the 100°C autoclaved sol had the minimum surface roughness of 4.1 nm and showed the minimum static contact angle of 115°. On the other hand, the sample prepared from the 180°C autoclaved sol had the maximum surface roughness of 9.5 nm and showed the maximum static contact angle of 134°. © 2011 The CeramicSociety of Japan.

DOI： 10.2109/jcersj2.119.591

Optical diagnostic of bipolar electrical discharges in HCl, KCl, and KOH solutions

Miron C., Bratescu M.A., Saito N., Takai O.

Journal of Applied Physics Vol. 109 ( 12 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

In this work, the characteristics of the plasma generated in HCl, KCl, and KOH solutions were analyzed using electrical and optical diagnostic techniques. Electrical discharges were initiated between two tungsten electrodes. Current and voltage characteristics have shown the features of a spark discharge for all of the solutions used in the experiment. The reactive species identified in the optical emission spectra depended on the type of solution used to generate the plasma. The time evolution of the reactive species depended on the nature of the solution and on the polarity of the applied pulse. The absorption spectra of the OH radical (X2 → A2∑+) were acquired when the voltage pulses were applied to the electrodes, with the intensity being lower in the regions between the pulses. The OH radical density was highest for the HCl solution plasma (2 × 1017cm -3) when positive voltage pulses were applied to the electrodes. © 2011 American Institute of Physics.

DOI： 10.1063/1.3597790

Generation of plasmas in water: Utilization of a high-frequency, low-voltage bipolar pulse power supply with impedance control

Baroch P., Potocky S., Saito N.

Plasma Sources Science and Technology Vol. 20 ( 3 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Sources Science and Technology

Presented work focuses on the investigation and characterization of plasma discharges generated in water by newly developed bipolar pulse power supply. The main aim of our work was to solve and overcome problems with intensive arc discharge transition when the discharge is ignited and maintained by a low output impedance pulse power supply. For this purpose a novel type of bipolar pulse power supply was developed and tested. It was found that two distinguished stable modes of discharges generated in the water can be realized. Effects of water conductivity, pulse frequency and initial water temperature on the discharge properties were investigated. Optical emission spectroscopy was employed to study plasma parameters of the discharge and the correlation between the data obtained from the optical emission spectroscopy and the chemical species measured in the water was carried out. © 2011 IOP Publishing Ltd.

DOI： 10.1088/0963-0252/20/3/034017

Corrosion Resistant Performances of Alkanoic and Phosphonic Adds Derived Self-Assembled Monolayers on Magnesium Alloy AZ31 by Vapor-Phase Method

Ishizaki, T; Okido, M; Masuda, Y; Saito, N; Sakamoto, M

LANGMUIR Vol. 27 ( 10 ) page： 6009 - 6017 2011.5

Analysis of organic pollutant degradation in pulsed plasma by coherent anti-Stokes Raman spectroscopy

Bratescu M., Hieda J., Umemura T., Saito N., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 29 ( 3 ) 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The degradation of p -benzoquinone (p -BQ) in water was investigated by the coherent anti-Stokes Raman spectroscopy (CARS) method, in which the change of the anti-Stokes signal intensity corresponding to the vibrational transitions of the molecule is monitored during and after solution plasma processing (SPP). In the beginning of SPP treatment, the CARS signal intensity of the ring vibrational molecular transitions at 1233 and 1660 cm-1 increases under the influence of the electric field of the plasma, depending on the delay time between the plasma pulse and the laser firing pulse. At the same time, the plasma contributes to the degradation of p -BQ molecules by generating hydrogen and hydroxyl radicals, which decompose p -BQ into different carboxylic acids. After SPP, the CARS signal intensity of the vibrational bands of p -BQ ceased and the degradation of p -BQ was confirmed by UV-visible absorption spectroscopy and liquid chromatography analysis. © 2011 American Vacuum Society.

DOI： 10.1116/1.3569035

Ag nanoparticle incorporation in mesoporous silica synthesized by solution plasma and their catalysis for oleic acid hydrogenation

Pootawang P., Saito N., Takai O.

Materials Letters Vol. 65 ( 6 ) page： 1037 - 1040 2011.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Letters

The incorporation of Ag nanoparticles on mesoporous silica as the supporting material and their catalysis for oleic acid hydrogenation were described in this study. The template removal and Ag nanoparticle incorporation were concurrently taken place in the novel glow discharge in a solution, namely solution plasma process under controlled conditions. With only 15 min of discharge time, Ag nanoparticles were incorporated on the mesoporous silica matrix confirmed by the evidences of XRD and TEM and the template inside mesopores was mostly removed confirmed by FTIR spectra. The hydrogenation catalysis of oleic acid was preliminarily tested using UV-VIS spectroscopy after oxidation using permanganate ions (MnO4-). It was found that the conversion was observed to be 12.83% in the butanol system and reached to 90.56% in ethanol. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2011.01.009

Fabrication of vertically aligned diamond whiskers from highly boron-doped diamond by oxygen plasma etching

Terashima C., Arihara K., Okazaki S., Shichi T., Tryk D.A., Shirafuji T., Saito N., Takai O., Fujishima A.

ACS Applied Materials and Interfaces Vol. 3 ( 2 ) page： 177 - 182 2011.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Conductive diamond whiskers were fabricated by maskless oxygen plasma etching on highly boron-doped diamond substrates. The effects of the etching conditions and the boron concentration in diamond on the whisker morphology and overall substrate coverage were investigated. High boron-doping levels (greater than 8.4×10 20 cm -3) are crucial for the formation of the nanosized, densely packed whiskers with diameter of ca. 20 nm, length of ca. 200 nm, and density of ca. 3.8 × 10 10 cm -2 under optimal oxygen plasma etching conditions (10 min at a chamber pressure of 20 Pa). Confocal Raman mapping and scanning electron microscopy illustrate that the boron distribution in the diamond surface region is consistent with the distribution of whisker sites. The boron dopant atoms in the diamond appear to lead to the initial fine column formation. This simple method could provide a facile, cost-effective means for the preparation of conductive nanostructured diamond materials for electrochemical applications as well as electron emission devices. © 2010 American Chemical Society.

DOI： 10.1021/am1007722

Structural properties and microstructures of SrTiO<inf>3</inf>/SrTi1-xNbxO3 superlattices grown by ion beam deposition

Panomsuwan G., Saito N., Takai O.

Materials Science Forum Vol. 695 page： 598 - 601 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Science Forum

Superlattice structure of SrTiO3 and Nb-doped SrTiO3 have been epitaxially grown on atomically flat surface of LaAlO3 substrates by ion beam deposition method. Epitaxial superlattices were grown at 800 °C in the presence of partial oxygen pressure under optimizing growth conditions. The Nb-doped SrTiO3 layers were varied from 2 to 15 unit cell thickness approximately, while SrTiO3 layers are maintained at 15 unit cell thickness with 10 periods. The superlattices with various Nb-doped SrTiO 3 layer thicknesses were investigated using X-ray diffractometer (XRD) and atomic force microscope (AFM), in order to clearly understand structural properties and surface structure, which are significant for fabrication of the high quality superlattice structure. © (2011) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.695.598

Synthesis of gold nanoparticles on petal-shaped silica by solution plasma

Yamamoto T., Ueno T., Zettsu N., Takai O., Saito N.

2011 Int. Symp. on Micro-NanoMechatronics and Human Science, Symp. on "COE for Education and Research of Micro-Nano Mechatronics", Symposium on "Hyper Bio Assembler for 3D Cellular System Innovation" page： 186 - 191 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：2011 Int. Symp. on Micro-NanoMechatronics and Human Science, Symp. on "COE for Education and Research of Micro-Nano Mechatronics", Symposium on "Hyper Bio Assembler for 3D Cellular System Innovation"

Spherical silica and gold nanoparticles were attempted to be prepared by solution plasma. The silica was prepared from the following solutions by solution plasma treatment. Those are (a) tetraethoxysilane, ethanol, water and hexadecylamine (TEOS-EtOH-H2O-HDA) system and (b) tetraethoxysilane, ethanol, water, hexade-cylamine and aurochloric acid (TEOS-EtOH-H2O-HDA-HAuCl4 ) system. In the system (a), the spherical silica was produced. While, in the system (b), gold nanoparticles supported petal-shaped silica were produced. These shapes differs from the one prepared from the conventional acid and base solutions stober method. © 2011 IEEE.

DOI： 10.1109/MHS.2011.6102224

Attenuated total reflectance spectroscopy of coumarin organosilane molecules adsorbed on a fused silica surface

Bratescu M., Saito N., Takai O.

Applied Surface Science Vol. 257 ( 5 ) page： 1792 - 1799 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

Attenuated total reflectance (ATR) spectroscopy was used to investigate the adsorption of coumarin organosilane molecules onto a fused silica surface. The difference between the absorption spectra of the molecules on the surface and in solution was explained by the interaction of the adsorbed coumarin organosilane molecules with the hydroxyl groups on the fused silica surface. This interaction produces a perturbation of the π electron distribution and the electronic transitions of the coumarin chromophore of the organosilane molecules adsorbed on the surface. From the kinetics adsorption curves, the calculated enthalpy values of 74.8 ± 5.2 kJ mol -1 and free energy of -38.22 ± 0.70 kJ mol -1 at 23 °C indicates a chemisorption process. The high sensitivity of ATR spectroscopy allows the detection of a monolayer formed by a 10 nM concentration of coumarin organosilane molecules, which covers more than half of the maximum surface coverage at 60 °C. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2010.09.019

OH production enhancement in bubbling pulsed discharges

Lungu C., Porosnicu C., Jepu I., Chiru P., Zaroschi V., Lungu A., Saito N., Bratescu M., Takai O., Velea T., Predica V.

AIP Conference Proceedings Vol. 1282 page： 115 - 118 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings

The generation of active species, such as H2O2, O*, OH*, HO2*, O3, N2*, etc, produced in aqueous solutions by HV pulsed discharges was studied in order to find the most efficient way in waste water treatment taking into account that these species are almost stronger oxidizers than ozone. Plasma was generated inside gas bubbles formed by the argon, air and oxygen gas flow between the special designed electrodes. The pulse width and pulse frequency influence was studied in order to increase the efficiency of the OH active species formation. The produced active species were investigated by optical emission spectroscopy and correlated with electrical parameters of the discharges (frequency, pulse width, amplitude, and rise and decay time). © 2010 American Institute of Physics.

DOI： 10.1063/1.3508527

A novel 3-dimensional cell culture system for embryoid bodies' formation

Zou X., Wu Y., Zhuang D., Zha G., Saito N., Takai O.

Proceedings - 2010 3rd International Conference on Biomedical Engineering and Informatics, BMEI 2010 Vol. 4 page： 1627 - 1632 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings - 2010 3rd International Conference on Biomedical Engineering and Informatics, BMEI 2010

Nano-structured films with super hydrophobic surfaces were fabricated by microwave-plasma enhanced chemical vapor deposition (MPECVD) method. It was found that water droplets with a volume from 10 to 30 μl rolled and bounced without wetting or spreading on the surfaces of the nanostructured films (nano films). After 3 days of cultivation, aggregation of embryoid body (EB) cells from embryonic stem (ES) cells were formed as microspheres on nano films coating in petri disks. Growth of ES cells was shown to be the best on the nano films with a 150° water contact angle. The EBs derived from ES cells cultured in droplets on the nano films grew over the cultivation time until the 7 th day on which EBs began to spread out. The results showed that the nano-structured film with a super-hydrophobic surface is a useful material for obtaining EBs from undifferentiated ES cells, this is anticipated to be a stem cell source for transplantation due to their pluripotency and indefinite proliferation. ©2010 IEEE.

DOI： 10.1109/BMEI.2010.5639591

FTIR study of methylene blue plasma degradation products through plasma treatment on water

Shirafuji T., Hieda J., Takai O., Saito N., Morita T., Sakai O., Tachibana K.

IEEE Region 10 Annual International Conference, Proceedings/TENCON page： 1938 - 1942 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Region 10 Annual International Conference, Proceedings/TENCON

Plasma treatment of methylene blue solution has been performed in Ar/Air gas-mixture atmospheric pressure plasma by using a specially designed "mangrove-type" electrode. In addition to the measurements of transmittance of the solution before and after the plasma treatment, FTIR investigation of the products after the treatment has been performed for understanding chemical effects of the treatment on the methylene blue molecular structure. ©2010 IEEE.

DOI： 10.1109/TENCON.2010.5686449

Solution plasma process for template removal in mesoporous silica synthesis

Pootawang P., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 49 ( 12 ) 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

The plasma discharge in aqueous solution was scientifically studied and applied to template removal in mesoporous silica synthesis. Highly dispersed spherical mesoporous silica particles were synthesized by the ternary surfactant system containing the Pluronic P123 copolymer (EO20PO 69EO20), sodium dodecylbenzene sulfonate, and 1,1,2,2,3,3,4,4,4-nonafluoro-1-butane sulfonate, via the sol-gel method in acid solutions. The solution plasma process (SPP), instead of conventional thermal calcinations, was used to remove the template. The mechanism of the removal of the organic template occurred via oxidation by the hydroxyl radicals generated during discharge. The transformation of a mesopore structure from a disordered wormlike structure to a hexagonally arranged structure was observed by X-ray diffraction analysis and was confirmed by transmission electron microscopy. The results of the thermal analysis and functional group identification of mesoporous silica after SPP showed evidence of organic template removal. The surface area calculated using the Brunauer-Emmett-Teller (BET) theory and the mean pore diameter results could be used to evaluate the plasma efficiency, demonstrating that this method does not affect the pore size in the case of discharge in a solution of pH 3 compared with the results of thermal calcination. Hence, SPP was proved to be highly efficient for organic template removal, exhibiting short consumption time and less contamination. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.49.126202

Time-resolved optical emission spectroscopy in water electrical discharges

Miron C., Bratescu M., Saito N., Takai O.

Plasma Chemistry and Plasma Processing Vol. 30 ( 5 ) page： 619 - 631 2010.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Chemistry and Plasma Processing

The characteristics of the plasma initiated in ultrapure water between pairs of tungsten and tantalum electrodes were investigated by time-resolved optical emission spectroscopy. The deexcitation processes of the reactive species formed in the water plasma depended on the electrode material, but had been independent on the polarity of the applied voltage pulses. All the reactive species presented the same evolution with time and have been identified with high concentration in the emission spectra between the pulses. The current-voltage characteristics showed the features of a spark discharge for the both types of electrodes used in the process. When tantalum electrodes were used to generate the discharge, a broad emission continuum (350-940 nm) dominated the spectrum due to a transition to arc discharge. ©Springer Science+Business Media, LLC 2010.

DOI： 10.1007/s11090-010-9248-1

Corrosion resistance and chemical stability of super-hydrophobic film deposited on magnesium alloy AZ31 by microwave plasma-enhanced chemical vapor deposition

Ishizaki T., Hieda J., Saito N., Saito N., Takai O.

Electrochimica Acta Vol. 55 ( 23 ) page： 7094 - 7101 2010.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

A super-hydrophobic film was successfully deposited on magnesium alloy AZ31 by the microwave plasma-enhanced chemical vapor deposition (MPECVD) process. The film surface showed a static water contact angle of more than 150°. The hydrophobicity and root mean square roughness of the film surface increased with an increase in deposition time. The anticorrosion resistance of the deposited film was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the super-hydrophobic film considerably improved the anticorrosion resistant performance of magnesium alloy AZ31. The anticorrosion mechanism of the super-hydrophobic film was also considered. Moreover, the chemical stability of the super-hydrophobic film in acidic, neutral, and alkaline aqueous solutions was investigated. The super-hydrophobic film showed high chemical stability in acidic and neutral aqueous solutions. © 2010 Elsevier Ltd.

DOI： 10.1016/j.electacta.2010.06.064

Oxygen gas barrier properties of hydrogenated amorphous carbon thin films deposited with a pulse-biased inductively coupled plasma chemical vapor deposition method

Baek S., Shirafuji T., Cho S., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 49 ( 8 PART 2 ) 2010.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Hydrogenated amorphous carbon (a-C:H) films have been deposited on poly(ethylene terephthalate) (PET) films with an pulse-biased inductively coupled plasma chemical vapor deposition method using CH4 and C 2H2 gases. We have investigated the effects of the pulse-bias frequency on the oxygen transmission rate (OTR) of the a-C:H-coated PET sample, and discussed relationship between the OTR characteristics and the structure of the films based on the results of Raman and infrared absorption spectroscopy. In case of CH4 plasmas, the OTR of the sample has been reduced down to 1.12 cm3/(m2.day.atm) by increasing the bias-frequency to 2 kHz, and the structure of the a-C:H films has been modified from polymer-like to tetrahedral one. In case of C2H2 plasmas, the OTR of the samples has been 1.18 cm3/(m 2.day.atm) with the lower bias frequency of 0.5 kHz, and has not shown strong dependence on the pulse-bias frequency. This has been explained by the fact that the films prepared with C2H2 plasma can be modified to tetrahedral structures by applying the bias with the lower frequency. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.49.08JF10

Effect of increasing hardness on Si-containing diamond-like carbon film during tribo-test

Kim S.G., Kim S.W., Saito N., Takai O.

Diamond and Related Materials Vol. 19 ( 7-9 ) page： 1017 - 1020 2010.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Diamond and Related Materials

In this study, silicon-DLC film has been especially treated by plasma-enhanced chemical vapor deposition (PECVD) process at 500 °C in the same chamber without compound-layer for enhancement of hardness and adhesion. The effects of different levels of silicon content on the silicon-containing DLC films were tested in air condition at room temperature with relative humidity using a ball-on-disk tribometer. After the wear test, Raman spectrum analysis on the tested surface of silicon DLC showed the changed structure on the surface. Especially, it has shown the increasing hardness value in proportional to increase TMS gas rate after wear test. At the same time, it was shown that ID/IG values increased higher G-peak values and positions on wear track of silicon-containing DLC surfaces. Therefore, the structure of the coated DLC surface changed between the wear-tested surface and the original surface. High silicon content DLC showed increased IG value with suddenly increased ID/IG value after the wear test. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2010.03.010

Fabrication and application of super-hydrophobic surface

Takai O., Ishizaki T., Saito N.

Toraibarojisuto/Journal of Japanese Society of Tribologists Vol. 55 ( 4 ) page： 254 - 259 2010.6

Correlation of cell adhesive behaviors on superhydrophobic, superhydrophilic, and micropatterned superhydrophobic/superhydrophilic surfaces to their surface chemistry

Ishizaki T., Saito N., Takai O.

Langmuir Vol. 26 ( 11 ) page： 8147 - 8154 2010.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 μm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 μm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface. © 2010 American Chemical Society.

DOI： 10.1021/la904447c

Needle electrode erosion in water plasma discharge

Potocký S., Saito N., Takai O.

Thin Solid Films Vol. 518 ( 3 ) page： 918 - 923 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

Various active species are formed by a pulsed electrohydraulic discharge. Analyses of optical emission spectra, hydrogen peroxide production and erosion of needle electrodes in the pulsed discharge in water with a pulse energy of ≈ 10 mJ were investigated in dependence on the type of plasma discharge (unbridged and bridged), the electrode material (tungsten and stainless steel) and the electrical conductivity of the solution (500, 750, 1000 and 1250 μS/cm). It was found that the OH radical emission line intensity was strongly intensified in the case of unbridged discharge mode independently on the electrode material or on solution conductivity. Hydrogen peroxide production did not depend on the electrode material and was not correlated with OH radical emission line intensity. Lower erosion rate was measured for tungsten electrodes with further decrease in the case of unbridged discharge mode of operation. Stainless steel electrodes reveal opposite characteristics. Smooth crater-like morphology was found for stainless steel and finer surface structures with protrusions for the tungsten with a smaller average crater diameter, shorter protrusion size and distribution for unbridged discharge mode of operation. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.07.172

Synthesis process of gold nanoparticles in solution plasma

Saito N., Hieda J., Takai O.

Thin Solid Films Vol. 518 ( 3 ) page： 912 - 917 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

We describe the dynamics of the synthesis of gold nanoparticles by a glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. The initial [AuCl4]- ion concentration and the voltage applied between the electrodes were varied. The [AuCl4]- ion was reduced by the H radicals generated in the discharge. The reduction rates were calculated from the changes in the [AuCl4]- ion concentration during the discharge time. Dendrite-shaped nanoparticles of about 150 nm size were formed in discharge during 1 min. The pH of the solution decreased gradually with the increase of the discharge time. The decrease in pH led to the dissolution of gold nanoparticles. The reduction and the dissolution rates increased proportionately with the applied voltage. The size of the gold nanoparticles decreased at 20 nm after running the discharge during 45 min. Moreover gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon were also observed. The particles were confirmed to be as polycrystalline gold nanoparticles by electron diffraction patterns. In summary, when the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in size in the solution. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.07.156

Solution plasma surface modification for nanocarbon-composite materials

Hieda J., Shirafuji T., Noguchi Y., Saito N., Takai O.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 73 ( 12 ) page： 938 - 942 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

Surface modification of carbon nanoballs (CNBs) using a plasma in liquid phase (solution plasma) and preparation of CNB/polyamide 6 (PA6) nanocomposite were demonstrated. Reactive species such as OH radical and H2O 2 generated from solution plasma oxidized the surface of CNBs and changed into hydrophilic. Mechanical properties (modulus of elasticity in tension and flexural modulus, especially impact strength) of hydrophilic CNB/PA6 composite were improved as compared to PA6 and untreated CNB/PA6 composite. CNBs with hydrophilic surface modified by solution plasma were well-dispersed into PA6 matrix. © 2009 The Japan Institute of Metals.

DOI： 10.2320/jinstmet.73.938

Study of protein adsorption onto a polymer film by in-situ UV attenuated total reflectance spectroscopy

Bratescu M., Fujita S., Saito N., Takai O.

Materials Research Society Symposium Proceedings Vol. 1138 page： 60 - 66 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Our work presents results on human plasma protein adsorption onto a polyacrylic acid (PAA) film prepared via surface wave plasma (SWP) induced graft polymerization. The PAA film prepared in this manner is characterized by a carboxyl functional group and a constant contact angle in water of 35°. The adsorption kinetics of human plasma fibrinogen (HPF) and human serum albumin (HSA) proteins were measured by in-situ UV-ATR spectroscopy. The free energy of adsorption on PAA treated as well as untreated surfaces was -28 kJ M -1 and -22 kJ M-1 for HPF and HSA, respectively, regardless of surface chemistry. We determined that 14 μM and 6 μM HPF concentrations are enough to cover half of the maximum possible of surface coverage on silica and PAA film, respectively. HSA protein concentrations of 154 μM and 118 μM are enough to cover half of the maximum accessible surface of silica and PAA film, respectively. For surface treatment of implants with PAA polymer and protein, the necessary protein concentration for effective surface coverage should be known. © 2009 Materials Research Society.

Biomimetic materials processing

Ishizaki T., Hieda J., Bratescu M.A., Saito N., Takai O.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 7404 2009.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

A biomimetic super-hydrophobic/super-hydrophilic micro-patterned surface was successfully fabricated by microwave plasma enhanced chemical vapor deposition (MPECVD) and vacuum ultraviolet (VUV) light lithography. On the micropatterned surface, various site-selective immobilizations were carried out. The fluorescent polystyrene spheres and copper were deposited site-selectively on super-hydrophobic regions using electrostatic interactions. The micropatterned surface brought the discrete adhesions of E. coli and B. subtilis specifically on super-hydrophobic regions. On the other hand, NIH 3T3 fibroblast cells attached to the super-hydrophilic regions in a highly selective manner. © 2009 SPIE.

DOI： 10.1117/12.829207

Fabrication of microtemplates for the control of bacterial immobilization

Miyahara Y., Mitamura K., Saito N., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 27 ( 5 ) page： 1183 - 1187 2009.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The authors described a region-selective immobilization methods of bacteria by using superhydrophobic/superhydrophilic and superhydrophobic/poly(ethylene glycol) (PEG) micropatterns for culture scaffold templates. In the case of superhydrophobic/superhydrophilic micropatterns, the superhydrophobic surface was prepared first by microwave-plasma enhanced chemical vapor deposition (MPECVD) from trimethylmethoxysilane. Then the superhydrophilic regions were fabricated by irradiating the superhydrophobic surface with vuv light through a stencil mask. In the case of the superhydrophobic/PEG micropatterned surfaces, PEG surfaces were fabricated first by chemical reaction of ester groups of p -nitrophenyl PEG with N H2 group of N H2 -terminated self assembled monolayer from n -6-hexyl-3-aminopropyltrimethoxysilane. The superhydrophobic regions were fabricated by MPECVD thorough a stencil mask. In this study four bacteria were selected from viewpoint of peptidoglycan cell wall (E. coli versus B. subtilis), extracellular polysaccharide (E.coli versus P. stutzeri, P. aeruginosa), and growth rate (P. stutzeri versus P. aeruginosa). The former micropattern brought discrete adhesions of E. coli and B. subtilis specifically on the hydrophobic regions, Furthermore, using the superhydrophobic/PEG micropattern, adhesion of bacteria expanded for E. coli, B. subtilis, P. stutzeri, and P. aeruginosa. They observed a high bacterial adhesion onto superhydrophobic surfaces and the inhibitive effect of bacterial adhesion on PEG surfaces. © 2009 American Vacuum Society.

DOI： 10.1116/1.3179158

Surfactant-assisted fabrication of tin oxide nanowires through one-step electrochemically induced chemical deposition

Ishizaki T., Saito N., Takai O.

Journal of the Electrochemical Society Vol. 156 ( 10 ) 2009.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society

Tin oxide nanowires were successfully fabricated at the potentials of -0.6 to -0.8 V from nitric acid electrolytes containing 20 mM tin dichloride, 100 mM sodium nitrate, 75 mM nitric acid, and 5 mM sodium dodecyl sulfate (SDS) through a one-step electrochemically induced chemical deposition. The addition of SDS surfactant to the nitric acid electrolyte led to a dramatic change in the shapes of the deposits, resulting in the formation of the tin oxide nanowires. Field emission scanning electron microscope and tunneling electron microscope images of the deposits showed that the diameter and the length of the tin oxide nanowires were within the range of 30-400 nm and several tens to hundreds of micrometers, respectively. X-ray diffraction and the selected area electron diffraction patterns of the deposits revealed that the tin oxide nanowire had a polycrystalline tetragonal structure. The shapes of the obtained samples changed with the SDS surfactant concentrations. The formation mechanism of the tin oxide nanowires is also discussed. © 2009 The Electrochemical Society.

DOI： 10.1149/1.3190161

Characterization of platinum catalyst supported on carbon nanoballs prepared by solution plasma processing

Ichin Y., Mitamura K., Saito N., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 27 ( 4 ) page： 826 - 830 2009.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

In order to improve the energy-conversion efficiency in fuel cells, the authors loaded Pt nanoparticles on carbon nanoballs (CNBs) by using solution plasma processing (SPP) involving CNB and Pt ion with a protection group. In this study, we employed poly(vinylpyrrolidone) (PVP) or sodium dodecyl sulfate (SDS) to prepare Pt nanoparticles supported on CNB (Pt/CNB) by the SPP, and the electrochemical properties as a catalyst was evaluated by cyclic voltammetry. The carbon nanoballs were prepared by thermal decomposition process of ethylene and hydrogen gases. Color of the solution changed from yellow to dark brown as synthesis time. This change indicates the improvement of dispersibility of CNB. Moreover, transmission electron microscopy images and elemental mapping images showed the Pt nanoparticles supported on CNB. A catalytic activity of the Pt/CNB in use of SDS was shown to be higher than the Pt/CNB prepared with PVP system. The SDS-containing Pt/CNB also showed the higher activity than that obtained by the conventional method. © 2009 American Vacuum Society.

DOI： 10.1116/1.3077285

Surface modification of gold nanorods by organosilanes

Mitamura K., Imae T., Saito N., Takai O.

Composite Interfaces Vol. 16 ( 4 ) page： 377 - 385 2009.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Composite Interfaces

Gold nanorods protected by hexadecyltrimethylammonium bromide were treated by an organosilane, aminopropyltriethoxysilane (APS) or vinyltrimethoxysilane (VS) in the presence of mercaptopropyltrimethoxysilane (MPS) serving as a binder. After the APS- or VS-treatment, a shell about 4 nm thick surrounding the nanorods was found by means of transmission electron microscopy. Its formation enabled the nanorods to be dispersed in polar media (ethanol, methanol, acetone and acetonitrile/water mixtures). © 2009 VSP.

DOI： 10.1163/156855409X447138

Self-assembly of human plasma fibrinogens on binary organosilane monolayers with micro domains

Lee S., Saito N., Takai O.

Applied Surface Science Vol. 255 ( 18 ) page： 7912 - 7917 2009.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

The adsorption behavior and self-assembly of human plasma fibrinogen (HPF) on binary methyl- and amino-terminated self-assembled monolayers (SAMs) were investigated by atomic force microscopy (AFM). The binary SAMs were fabricated through self-assembly mechanism of organosilane molecules. The height of domains is the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the difference between the length of the alkyl chain of octadecyltrichlorosilane (OTS) and that of n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS). The fibrinogen solution used ultrapure water as the solvent and its pH was adjusted at 3 and 10. From the AFM results at pH 3, HPF only formed network structures on the OTS domains of the binary SAM at early immersion times, and then the network structures expanded and connected between OTS domains through the AHAPS surface at long immersion times. In this case, a few HPFs are discretely adsorbed on the AHAPS surface. However, HPF is uniformly adsorbed on the binary SAM under the other conditions of pH. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2009.04.201

Highly reproducible technique for three-dimensional nanostructure fabrication via anodization scanning probe lithography

Lee S.H., Saito N., Takai O.

Applied Surface Science Vol. 255 ( 16 ) page： 7302 - 7306 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

The effects of coated materials for Si probes on the sizes of line structure by using anodization scanning probe lithography (SPL) are investigated by using atomic force microscopy (AFM). Anodization SPL was carried out on the 1-decane monolayer directly attached to hydrogen-terminated silicon. Gold-coated, diamond-coated, and uncoated Si probes were used as the SPL probes in order to fabricate line structures of silicon oxide. In the cases of Au-coated and uncoated Si probes, the widths of line structures are widely influenced by the changes of scanning rate and applied bias voltage. However, the line width fabricated by use of the diamond-coated probe maintained 15 nm under any condition of scanning rate and applied bias voltage. One of the most narrow and three-dimensional nanostructures is found to be successfully fabricated on the hydrogen-terminated Si substrates when the diamond-coated probe was used as a probe of anodization SPL. In addition, this result indicated that high reproducibility of oxide nanostructures is attainable by anodization SPL used the diamond-coated probe. © 2009.

DOI： 10.1016/j.apsusc.2009.03.087

Adsorption of protein on polyelectrolyte brush surface

Higuchi, A; Tatematsu, H; Fujima, T; Saito, N; Takai, O

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 237 2009.3

Chemical dynamics of protein adsorption and desorption on regulated surfaces in aqueous solutions

Saito, N; Hieda, J; Takai, O

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 237 2009.3

Bioreorganization surface with hierarchical structure

Takai, O; Saito, N; Sato, H; Miura, Y; Kobayashi, K

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 237 2009.3

Effects of humidity on the friction coefficient of diamond-like carbon (DLC) coating

Kim S.G., Cho Y.K., Jang W.S., Kim S.W., Nagahiro S., Takai O.

Journal of the Korean Physical Society Vol. 54 ( 3 ) page： 1228 - 1236 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Korean Physical Society

A diamond-like Carbon (DLC) coating has been known to be a good tribological problem solver due to its low friction characteristics and high hardness. The friction coefficient values shown in the literature surveyed differ from the authors' due to different test conditions. When we plot these results and our own with the variable of humidity, the friction coefficient decreases with increasing environmental humidity. By using contact angle measurements to study the interface properties of these coatings, we conclude that this change comes from the hydrophilic and the hydrophobic properties of the surface and the eventual change of the wear mode. DLC films were deposited on SKD11 steel by using pulsed (DC PECVD) (a-CH, hydrogenated DLC, Si-containing DLC) and amorphous carbon filtered arc DLC (a-C, non-hydrogenated DLC). Deposited DLCs were tested according to humidity by using a tribometer. We used a SUJ2 (JIS standard) steel ball bearing for the counterpart of wear test. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and surface roughness testers were used for surface analysis of the DLC and the wear trace. The Raman spectra of the films showed that the carbon bonding structures changed according to the I(D)/I(G) intensity ratio for the wear trace at severe wear conditions. In normal humidity, 30-85 % RH, the DLC had a friction coefficient lower than it did in 5 % RH. In this case, the Si-containing hydrogenated DLC definitely had the lowest friction coefficient. Eventually, it also had the lowest contact angle, as expected. When we investigated two different kinds of DLCs in terms of hydrogen content, we observed the same effect of relative humidity on friction behavior.

DOI： 10.3938/jkps.54.1228

Friction behavior of diamond-like carbon coating with relative humidity

Kim S., Saito N., Otake N., Kim S., Takai O.

Proceedings of the 17th IFHTSE Congress Vol. 1 page： 373 - 376 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 17th IFHTSE Congress

Owing to the intrinsic beneficial tribological properties of DLC coating, it has attracted many researcher's interest in better understanding of wear phenomena. In this study, DLC films show a tendency to decrease the friction coefficient value as the humidity increases. These results come from a change in the hydrophilic and hydrophobic properties of DLC films through the evolution of the contact angle of interface with humidity. DLC films were deposited on SKD11 steel by filtered arc DLC (a-C, non-hydrogenated DLC) and pulsed DC PECVD (a-C:H, hydrogenated DLC and Si-containing hydrogenated DLC). Wear tests of the DLC films were carried out with a ball-on- disk tribometer machine in different level of humidity. In contrast to what had been expected, the wear volume of a-C:H DLC, which has the lower friction coefficient than a-C DLC, seems important the wear were occurred through first adhesive wear type and followed by producing small-sized DLC debris between the tribology system and finally the abrasive mode. In the case of the non-hydrogenated DLC wear test at the same condition, microscopic observation showed that the final abrasive wear occurred through the sliding small-size hydrophobic debris formed between the steel counter partner and the DLC coating layer. At the same humidity condition, the Si-containing hydrogenated a-C:H DLC showed different wear behavior that was caused by hydrophilic agglomerated debris. A large area seemed to be worn away for the DLC films and eventually Fe<inf>3</inf>O<inf>4</inf> comes out with Fe<inf>3</inf>O<inf>4</inf>from the substrate. Even though, the friction coefficient of hydrogenated DLC was lower, the wear loss seemed to be more severe due to the agglomeration of debris and the wear mode shift in the dry condition evaluation of tribological characteristic of DLC cannot be done by a simple index. The other side, at the normal humidity (30-85% RH) condition, the Si-containing hydrogenated DLC showed a very low friction coefficient with small wear volume compared to the dry condition. In a similar manner the non-hydrogenated DLC showed a gradual lower friction coefficient as the humidity increased.

Morphological control of vertically self-aligned nanosheets formed on magnesium alloy by surfactant-free hydrothermal synthesis

Ishizaki, T; Cho, SP; Saito, N

CRYSTENGCOMM Vol. 11 ( 11 ) page： 2338 - 2343 2009

High frequency bipolar pulsed spark electrohydraulic discharge characteristics and plasma parameters of liquid solution plasmas

Miron C., Chang J.S., Takeda T., Saito N., Takai O.

GD 2008 - 17th International Conference on Gas Discharges and Their Applications page： 489 - 492 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：GD 2008 - 17th International Conference on Gas Discharges and Their Applications

An experimental investigation has been conducted to study fundamental electrohydraulic discharge characteristics and plasma parameters of liquid solution plasmas. HF-bipolar high voltage was supplied to the rod-to-rod type plate electrodes with a few mm gap distance inside water with conductive KCl or Na2SO4 solutions. Experiments are conducted for applied maximum voltage from 1 to 6 kV, the electrode gap distances from 0.3 to 5 mm and for the operating frequency from10 to 15 kHz. Plasma parameters was determined by the optical emission spectroscopy with LTE model and compared with the discharge channel averaged plasma parameter from discharge characteristics. The results show that a stable, liquid solution plasma can be generated by HF PSED. Based on optical emission spectra, a significant hydrogen gas was generated in a spark discharge channel. Morphology of liquid solution plasma and transient plasma density behavior will be discussed in detail.

Reaction Dynamics for Gold Nanoparticles Synthesis in Solution Plasma

Hieda J., Saito N., Takai O.

Materials Research Society Symposium Proceedings Vol. 1056 page： 221 - 226 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

We describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl4]- concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl 4]- vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl4]- was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles -150 nm in size were formed after discharge for 1 mm. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 mm. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution. © 2008 Materials Research Society.

Fundamental electrohydraulic discharge characteristics and plasma parameters of dielectric liquid dodecane with Ar gas injections for gold nano-particle fabrications

Hieda J., Chang J.S., Saito N., Takai O.

2008 IEEE International Conference on Dielectric Liquids, ICDL 2008 2008.11

Language：English Publishing type：Research paper (scientific journal) Publisher：2008 IEEE International Conference on Dielectric Liquids, ICDL 2008

An experimental investigation has been conducted to study a fundamental electrohydraulic discharge characteristics and plasma parameters in a dielectric liquid solution with Ar gas injections. HF-bipolar high voltage was supplied to the converging angle type plate electrodes with 1mm gap distance inside dodecane with conductive salt solutions. Experiments are conducted for Ar gas flow rate from 0.1 to 1 L/min., applied maximum voltage from 10 to 60 kV for the operating frequency fromlO to 15 kHz. The results show that HF PSED can be generated relatively stable discharge even in the dielectric fluid and gold nano-particles were fabricated. Morphology of liquid solution plasma and transient plasma density behavior will be discussed in detail.

DOI： 10.1109/ICDL.2008.4622477

Nano/Micro Patterning of Inorganic Thin Films

Koumoto, K; Saito, N; Gao, YF; Masuda, Y; Zhu, PX

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 81 ( 11 ) page： 1337 - 1376 2008.11

Surface characterization on binary nano/micro-domain composed of alkyl- and amino-terminated self-assembled monolayer

Lee S.H., Ishizaki T., Saito N., Takai O.

Applied Surface Science Vol. 254 ( 22 ) page： 7453 - 7458 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

The binary alkyl- and amino-terminated self-assembled monolayers (SAMs) composed of nano/micro-sized domains was prepared though a self-assembly technique. In addition, the wetting and electrostatic property of the binary SAMs was investigated by the analysis of the static and dynamic water contact angle and zeta-potentials measurement. The binary SAMs were also characterized by atomic force microscope (AFM), Kelvin probe force microscope (KPFM) and X-ray photoelectron spectroscopy (XPS). The domains on the binary SAMs were observed in topographic and surface potential images. The height of domain and the surface potential between octadecyltrichlorosilanes (OTS)-domain and n-(6-aminohexl)aminopropyl-trimethoxysilane (AHAPS)-SAM were about 1.1 nm and -30 mV. These differences of height and surface potential correspond to the ones between OTS and AHAPS. In XPS N 1s spectra, we confirmed the formation of binary SAMs by an amino peak observed at 399.15 eV. The dynamic and the static water contact angles indicated that the wetting property of the binary SAMs was depended on the OTS domain size. In addition, static water contact angles were measured under the conditions of different pH water and zeta-potential also indicated that the electrostatic property of the binary SAMs depended on OTS domain size. Thus, these results showed that the wetting and electrostatic property on the binary SAMs could be regulated by controlling the domain size. © 2008.

DOI： 10.1016/j.apsusc.2008.06.001

Control of site-selective adsorption reaction on a biomimetic super-hydrophilic/super-hydrophobic micropatterned template

Ishizaki T., Sakurai H., Saito N., Takai O.

Surface and Coatings Technology Vol. 202 ( 22-23 ) page： 5535 - 5538 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

A biomimetic super-hydrophobic/super-hydrophilic micropatterned template was successfully fabricated by microwave plasma-enhanced chemical vapor deposition (MPECVD) and vacuum ultraviolet (VUV) lithography. Water drops were selectively condensed on super-hydrophilic regions of the template. In the solution of pH 2.6, carboxyl-terminated fluorescent polystyrene spheres were sedimented on super-hydrophobic regions due to electrostatic attractive forces between negative -COO- and positive -CH3 groups. Cu was also deposited densely on only super-hydrophobic regions through electroless plating. From these results, we revealed that the biomimetic super-hydrophobic/super-hydrophilic micropatterned template was used as site-selective chemical reaction field. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2008.06.124

Influence of Ar gas flow rate in organosilicon plasma for the fabrication of SiO:CH thin films by PECVD method

Yun Y., Yoshida T., Shimazu N., Nanba N., Inoue Y., Saito N., Takai O.

Surface and Coatings Technology Vol. 202 ( 22-23 ) page： 5259 - 5261 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

SiO:CH films were prepared by capacitively coupled RF PECVD to investigate the dependence on Ar gas flow ratio based on plasma reactions and film properties. The introduced Ar gas flow rate increases an the amorphous carbon network, and dangling bonds or -OH terminations due to Ar ion bombardment. Moreover, Ar gas flow rate alters the dissociation reactions and leads to change the chemical bonding states and the water contact angle. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2008.06.004

Size-regulated gold nanoparticles fabricated by a discharge in reverse micelle solutions

Hieda J., Saito N., Takai O.

Surface and Coatings Technology Vol. 202 ( 22-23 ) page： 5343 - 5346 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

A discharge was applied to reverse micelle solutions, which provided constant volume nanoreactors, to synthesize size-regulated gold nanoparticles. The molar ratio of water to surfactant, W, was varied to regulate the nanoparticle size. A pulsed power supply was used to generate the discharge in the reverse micelle solutions. The applied voltage, pulse width, and frequency were 960 V, 2 μs, and 15 kHz, respectively. The synthesized gold nanoparticles were observed by transmission electron microscopy (TEM). Surface plasmon absorption band of the gold nanoparticles was measured by ultraviolet-visible (UV-Vis) spectroscopy. TEM images showed that the average particle size varied from 3.8 to 11 nm in diameter as W was increased. Thus, the size of gold nanoparticles can be regulated by the volume of water droplets in the reverse micelle solutions. Reduction of [AuCl4]- ions and formation of gold nanoparticles proceeded only inside the water droplets formed by reverse micelles. These nanoreactors regulated by reverse micelles lead to the uniform growth of gold nanoparticles. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2008.06.092

Effect of reaction temperature on growth of organosilane self-assembled monolayers

Lee S., Ishizaki T., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 47 ( 8 PART 1 ) page： 6442 - 6447 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The effect of reaction temperature on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) self-assembled monolayers (SAM) was investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD) measurement, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). OTS SAM was prepared by a liquid phase method and chemical vapor deposition. In the liquid phase method, OTS SAM was prepared in the temperature range from 5 to 40 °C. In the reaction temperature range from 5 to 30 °C, OTS molecules formed domain structures early in the growth process and grew two-dimensionally on SiO2 substrates. In addition, the crystalline peaks of GIXD measurements indicated that OTS SAM prepared at lower temperatures (5-30 °C) grew in the crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS SAM prepared at 40 °C showed an amorphous structure. XPS and FT-IR spectra showed that the SiO2 peak increased while reaction temperature decreased. These results indicated that the formation of a siloxane bond between OTS molecules was important for the self-organization of the OTS monolayer. In addition, FT-IR measurement indicated that the packing density of the OTS monolayer prepared at lower temperatures was higher than that prepared at higher temperatures by chemical vapor deposition. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.6442

Effects of humidity and solution age on growth of organosilane self-assembled monolayers

Lee S., Ishizaki T., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 47 ( 8 PART 1 ) page： 6416 - 6421 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The effect of humidity on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) monolayers was investigated using an atomic force microscope (AFM), grazing incidence X-ray diffraction (GIXD), and Fourier transform IR spectroscopy (FT-IR). OTS self-assembled monolayers (SAMs) were prepared under humidity ranging from 5 to 80%. Under humidity ranging from 15 to 80%, OTS molecules produced domain structures early in the growth process that grew twodimensionally on SiO2 substrates. Also, the crystalline peaks of the obtained from the GIXD measurement indicated that OTSSAMs prepared under high humidity (15-80%) had grown in a crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS-SAMs prepared under 5% humidity were in an amorphous structure. OTS-SAMs prepared at high humidity were denser than those prepared at low humidity. The domain size early in the growth process increased in proportion to the solution age. This shows that the reaction rate is governed by the hydrolysis of organosilane. On the other hand, solution age has no great influence on the density of the OTS-SAMs under conditions of more than 50% humidity. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.6416

Bipolar pulsed electrical discharges in liquid

Baroch P., Saito N.

IEEE Transactions on Plasma Science Vol. 36 ( 4 PART 1 ) page： 1156 - 1157 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Plasma Science

Electrical discharges in water offer a unique plasma source which can be utilized in various novel applications. These discharges are distinguished for the rapid in situ production of highly reactive species when high voltage of about 10-20 kV is applied. Images of the plasma discharges in the water, which are generated by using high-frequency bipolar pulse power supply at relatively low ignition voltages, are presented here. © 2008 IEEE.

DOI： 10.1109/TPS.2008.924488

Morphology of high-frequency electrohydraulic discharge for liquid-solution plasmas

Takeda T., Chang J.S., Ishizaki T., Saito N., Takai O.

IEEE Transactions on Plasma Science Vol. 36 ( 4 PART 1 ) page： 1158 - 1159 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Plasma Science

An experimental investigation has been conducted to study the morphology of high-frequency electrohydraulic discharge for a liquid-solution plasma, where the liquid-solution plasma is currently investigated for the fabrication of nanometer-size metal particles and inactivation of bacteria. The fundamental nature and basic characteristics of this new type of plasma is relatively not well investigated. In this paper, this type of liquid-solution plasma was experimentally investigated along with discharge morphology. © 2008 IEEE.

DOI： 10.1109/TPS.2008.925713

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Hieda J., Saito N., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 26 ( 4 ) page： 854 - 856 2008.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2 O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2 O2 and electron donation of H radicals to the solution. After the pH stopped decreasing, H radicals mainly reacted as a reducing agent. The decrease in pH allowed redissolution of the gold nanoparticles. The gold dust particles that were not completely dissolved acted as new seeds for nucleation. Thus, the two reaction steps, nucleation and nuclear growth, occur during the formation of gold nanoparticles with exotic shapes. © 2008 American Vacuum Society.

DOI： 10.1116/1.2919139

Bipolar pulsed electrical discharge for decomposition of organic compounds in water

Baroch P., Anita V., Saito N., Takai O.

Journal of Electrostatics Vol. 66 ( 5-6 ) page： 294 - 299 2008.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Electrostatics

This work focuses on the development of an underwater plasma source that may open new possibilities in wastewater treatment processes by enabling the operation of the discharge under relatively low discharge voltages (sub-kV region). For this purpose, two systems, based on a wire-to-wire electrode configuration: (i) with and (ii) without gas bubbling, were designed. Both systems were operated utilizing a high-frequency bipolar DC pulse power supply. Properties of generated plasma were investigated by electrical and optical emission spectroscopy methods. Subsequently, determination of generation of active species and preliminary tests on the decomposition of organic dye in aqueous solution were carried out. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elstat.2008.01.010

Special type of plasma dielectric barrier discharge reactor for direct ozonization of water and degradation of organic pollution

Baroch P., Saito N., Takai O.

Journal of Physics D: Applied Physics Vol. 41 ( 8 ) 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

A system based on the dielectric barrier discharge (DBD) with improved discharge homogeneity, used for direct ozonization and purification of water, is presented here. A special design of the atmospheric DBD system is characterized by incorporation of a porous ceramic segment in the zone between electrodes. This porous segment was placed on the metallic electrode and served as a guide for flowing water. Due to the hydrophilic force it allowed the water to remain undisturbed by the electrical discharge. This feature enabled a reduction of the discharge gap and subsequently an increase in the intensity, stability and homogeneity of the discharge. It was observed that under such a configuration a transition from the filamentary mode to the semi-homogeneous mode of the plasma discharge could be realized. Discharge properties were investigated by the optical emission spectroscopy method and the results showed the domination of nitrogen lines in the UV-A region. Further it was observed that the system can be operated in a wide range of liquid conductivities and under negligible heat deposition to the liquid solution. Finally, the formation of dissolved ozone and hydrogen peroxide in the deionized water was measured and decomposition tests with organic dye were performed. © 2008 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/41/8/085207

Attenuated total reflectance spectroscopy of simultaneous processes: Corrosion inhibition of cuprous oxide by benzotriazole

Bratescu M.A., Allred D.B., Saito N., Sarikaya M., Takai O.

Applied Surface Science Vol. 254 ( 10 ) page： 2960 - 2966 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

Attenuated total reflectance (ATR) spectroscopy was used to perform in situ studies of the corrosion inhibition of cuprous oxide (Cu 2 O) by benzotriazole (BTA) in aqueous solution at concentrations from 1 to 20 μM. Because two separate processes occur simultaneously, that of Cu 2 O corrosion and corrosion inhibition by BTA adsorption, the spectral information was subjected to deconvolution by a conjugate gradient minimization algorithm. Under these conditions, a solution phase concentration of 7-10 μM BTA nearly completely inhibited the corrosion of Cu 2 O in deionized water. Using a Langmuir adsorption model, this represented only 25% of the maximally covered surface area. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2007.10.048

Scanning probe microscopy for the analysis of composite Ti/hydrocarbon plasma polymer thin films

Choukourov A., Grinevich A., Slavinska D., Biederman H., Saito N., Takai O.

Surface Science Vol. 602 ( 5 ) page： 1011 - 1019 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Composite Ti/hydrocarbon plasma polymer films with different Ti concentration were deposited on silicon by dc magnetron sputtering of titanium in an atmosphere of argon and hexane. As measured by Kelvin force microscopy and visco-elastic atomic force microscopy, respectively, surface potential and hardness increase with increasing Ti content. Adhesion force to silicon and to fibrinogen molecules was stronger for the Ti-rich films as evaluated from the AFM force-distance curves. Fibrinogen forms a very soft layer on these composites with part of the protein molecules embedded in the outermost region of the plasma polymer. An increase of the surface charge due to fibrinogen adsorption has been observed and attributed to positively charged αC domains of fibrinogen molecule. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.12.035

Comparative study of the molecular aggregation state of alkyl organic monolayers prepared on Si and hydrogen-terminated Si substrates

Ishizaki T., Saito N., Lee S., Takai O.

Nanotechnology Vol. 19 ( 5 ) 2008.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

A comparative study of the molecular aggregation states of n-octadecyltrichlorosilane (OTS) and octadecene monolayers was carried out based on water contact angle, x-ray reflectivity (XR), grazing incidence x-ray diffraction (GIXD), and Fourier transform infrared spectroscopy (FT-IR) measurements. Water contact angle, XR, and FT-IR measurements revealed that the packing density and orientational order of the OTS were higher than those of octadecene. The OTS monolayer was in a hexagonal crystalline state with (10) spacing of 0.417 nm, whereas the octadecene monolayer was in an amorphous state. The growth mechanisms of the OTS and octadecene monolayers are also proposed. The alkyl molecular aggregation states strongly depended on the chemical bonding state at the interface between the alkyl organic molecule and the substrate surface. © IOP Publishing Ltd.

DOI： 10.1088/0957-4484/19/05/055601

'Fabrication and structure of alginate gel incorporating gold nanorods

Mitamura K., Imae T., Saito N., Takai O.

Journal of Physical Chemistry C Vol. 112 ( 2 ) page： 416 - 422 2008.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

The gelation of sodium alginate incorporating gold nanorods was investigated. The hybrid gel was obtained by mixing calcium ions with a gel precursor (alginate + nanorod). The gel displayed two plasmon bands in the visible and near-infrared region. The shapes of the hybrid gel grains were controllable, like sphere, ring, and rod. Furthermore, the release of the gold nanorods from the gel phase was observed in a saline solution, accompanying the gel collapse to alginate fibers. Moreover, in the structural investigation of the hybrid gel using small-angle X-ray scattering, it was confirmed that alginate fibers were tightly condensed on the nanorod and formed a shell on it. Such condensation or shell formation resulted from the electrostatic interaction of alginate with hexadecyltrimethylammonium bromide, which protects the nanorods. The hybrid gel retained the same amount of water as the neat gel, although the water content (30 wt %) in a shell on a nanorod was far less than that (98 wt %) of bulk gel. © 2008 American Chemical Society.

DOI： 10.1021/jp076755a

Radio frequency power dependence in formation of SiO:CH thin films by plasma-enhanced chemical vapor deposition

Yun Y., Yoshida T., Shimazu N., Nanba N., Inoue Y., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 46 ( 11 ) page： 7460 - 7464 2007.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

SiO:CH films were prepared by capacitively coupled radio frequency (RF) plasma-enhanced chemical vapor deposition to investigate the dependence on RF power on the basis of plasma reactions and film properties. The RF power dependence can be divided into two broad categories, the reaction-controlled regime (regime R) and the flow rate-controlled regime (regime F). In the regime R, the introduced RF power initially dissociates and recombines the trimethylmethoxysilane reactant, and leads to drastic increase in deposition rate. In the regime F, the insufficient flow of reactants saturates the deposition rate. Moreover, the extra energy dissociates and recombines the reactant drastically and heats electrons in the plasma. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.7460

Application of Ultra-Water-Repellent Surface to Cell Culture

Ino K., Ito A., Wu Y., Saito N., Hibino E., Takai O., Honda H.

Journal of Bioscience and Bioengineering Vol. 104 ( 5 ) page： 420 - 423 2007.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Bioscience and Bioengineering

In this study, we applied an ultra-water-repellent film to cell culture. We cultured cells in droplets on the film and fabricated cell aggregates. Furthermore, we allocated cells on micropatterned surfaces consisting of ultra-water-repellent regions and cell culture-treated regions. The results show that the material is useful for cell culture. © 2007 The Society for Biotechnology, Japan.

DOI： 10.1263/jbb.104.420

A micropatterned carbohydrate display for tissue engineering by self-assembly of heparin

Sato H., Miura Y., Saito N., Kobayashi K., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3871 - 3875 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

A novel strategy to construct a fibroblast scaffold on substrates has been demonstrated via top-down photolithography and the subsequent bottom-up processes of molecular self-assembly and molecular recognition. 3-Aminopropyltrimethoxysilane (APS) self-assembled monolayer was micropatterned by photolithography. An anionic polysaccharide heparin was adsorbed selectively on the cationic APS region of the micropatterned substrate. Basic fibroblast growth factor (bFGF) was selectively bound to the displayed heparin region and then micropatterned cultivation of fibroblast cells was successful on the bFGF-heparin-APS substrate. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.066

Electrochemical soft lithography of an 1,7-octadiene monolayer covalently linked to hydrogen-terminated silicon using scanning probe microscopy

Lee S.H., Ishizaki T., Saito N., Takai O.

Surface Science Vol. 601 ( 18 ) page： 4206 - 4211 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Electrochemical scanning probe lithography (SPL) was carried out on a 1,7-octadiene (OD) monolayer directly attached to silicon. The chemical conversion of the OD-monolayer was investigated by Kelvin probe force microscopy (KPFM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and by an adsorption test of amino-modified fluorescent spheres. AFM and KPFM results indicated that the electrochemical reactions induced by SPL were governed by the bias voltage applied between the tip of the scanning probe microscope (SPM) and the substrate. XPS spectra indicated that the vinyl groups on the OD monolayer were oxidized and chemically converted into carboxyl groups at bias voltages of 1-2 V. At bias voltages of more than 3 V, OD molecules on the sample surface were decomposed and silicon oxide was formed on the surface. In addition, the formation of COOH groups was confirmed by the site-selective adsorption of amino-modified fluorescent spheres. However, XPS spectra for sample surfaces scanned at negative bias voltages showed no change since the peak was generally weak. However, KFM and AFM results indicated that at bias voltages of more than -1.5 V, cyclobutane rings formed. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.094

Localized surface plasmon resonance of silicon compounds adsorbed on silver nanoparticles

Bratescu M., Saito N., Mori H., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3886 - 3891 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

A simple method to produce silver nanoparticles on a glass surface from silver nanolayer deposited by magnetron sputtering and thermal annealed is presented. Localized surface plasmon resonance of nanoparticles shows a red shift depending on the silver nanolayer thickness, the refractive index and the thickness of an ultra-thin silicon compound adsorbed on the surface. A highly enhanced Raman spectrum of the characteristic groups of a silicon compound adsorbed on the nanoparticles surface was obtained. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.074

SPM analysis of fibrinogen adsorption on solid surfaces

Choukourov A., Grinevich A., Saito N., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3948 - 3951 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

The adsorption kinetics, adhesion and orientation of human fibrinogen on solid surfaces have been studied by surface probe microscopy (SPM) and quartz crystal microbalance techniques (QCM). CF3-, NH2-terminated organo-silane self-assembled monolayers (SAM) and OH-terminated silicon dioxide have been used as model surfaces. Furthermore, the interaction of fibrinogen with nanocomposite Ti/hydrocarbon plasma polymer films (Ti/ppCH) deposited by dc magnetron sputtering has also been studied. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.155

Probing into adsorption behavior of human plasma fibrinogen on self-assembled monolayers with different chemical properties by scanning probe microscopy

Ishizaki T., Saito N., Sato Y., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3861 - 3865 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

The adsorption behaviors of fibrinogen on the self-assembled monolayers (SAMs) with different chemical properties were investigated using an atomic force microscopy (AFM). AFM images indicated that the adsorption amounts of fibrinogen molecules increased with an increase of the surface hydrophobicity. High-resolution AFM imaging revealed that the fibrinogen conformations adsorbed on the SAM surface changed with dependent on the surface chemistry. The adsorption models of fibrinogen molecules adsorbed on SAM surfaces with different chemical properties were proposed based on the high-resolution AFM images. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.096

Local generation of carboxyl groups on an organic monolayer through chemical conversion using scanning probe anodization

Lee S., Ishizaki T., Saito N., Takai O.

Materials Science and Engineering C Vol. 27 ( 5-8 SPEC. ISS. ) page： 1241 - 1246 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Science and Engineering C

An organic monolayer directly attached to silicon was prepared through a reaction between 1,7-octadien (OD) and hydrogen-terminated silicon. The OD-monolayer had H2C-terminated groups. The properties of OD-monolayer were evaluated by atomic force microscopy (AFM), ellipsometry and water contact angle measurements. The H2C-terminated groups were site-selectively oxidized through scanning probe anodization and ultraviolet (VUV) irradiation. The sample surfaces fabricated were evaluated by Kelvin force probe microscopy (KPFM) and X-ray photoelectron spectroscopy (XPS). Chemical conversion of functional group in the OD-monolayer was evaluated based on the surface potential change and the immobilization of fluorescence-labeled spheres onto the sample surfaces. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2006.07.002

Fabrication and self-assembly of hydrophobic gold nanorods

Mitamura K., Imae T., Saito N., Takai O.

Journal of Physical Chemistry B Vol. 111 ( 30 ) page： 8891 - 8898 2007.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Hydrophobic gold nanorods were fabricated from hydrophilic gold nanorods coated with hexadecyltrimethylammonium bromide by treating with mercaptopropyltrimethoxysilane (MPS) and subsequently octadecyltrimethoxysilane (ODS). The fabrication of the hydrophobic shell went through the process of (1) binding MPS onto the nanorods, (2) hydrolysis of methoxysilanes, and (3) immobilization of ODS by dehydration condensation. The 2- or 3-D ordered structures of hydrophobic nanorods were self-assembled by the evaporation of solvent on a substrate. The aspects of 2-D assemblies were dependent on the concentration of the nanorods, as was seen in transmission electron microscopic images. At a low concentration, the nanorods assembled parallel to the substrate, whereas they stood on the substrate at a high concentration. On the other hand, in a solid of the gold nanorods, the formation of the 3-D assembly was confirmed by small-angle X-ray scattering. The assembly consisted of hexagonal arrays of the gold nanorods and their lamellar accumulation. © 2007 American Chemical Society.

DOI： 10.1021/jp072524s

Atmospheric plasma-calcination of mesoporous tungsten oxide utilizing plasma dielectric barrier discharge

Baroch P., Hieda J., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 12 ) page： 4905 - 4908 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

The fabrication of mesoporous tungsten oxide films by spin-coating method followed by an atmospheric plasma-calcination method is described and discussed here. For the calcination process the dielectric barrier discharge system generating homogenous atmospheric plasma discharge was designed and used. By this method, large surface area mesoporous films, with disordered pores of average diameter size of about 4 to 5 nm were synthesized. All the plasma-calcined films exhibit amorphous structure. The process of calcination was evaluated by FT-IR spectroscopy and in comparison with other methods a very high speed of calcination process was achieved. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.10.088

Submicron optical near-field diffraction patterns obtained by irradiation of octadecyltrimethoxysilane self-assembled monolayers with light at 157 nm

Nae F., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 12 ) page： 5147 - 5152 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

Nanostructures less than 200 nm in size are created by the Fresnel diffraction of 157 nm light at the aperture margins of a photomask through proximity irradiation of an octadecyltrimethoxysilane self-assembled monolayer. Photochemical decomposition of the organic monolayer creates complex nanostructure patterns, according to the light intensity distribution at the substrate location. Dimensions and distribution of the nanostructures correlate well with the spatial distribution of the light intensity calculated using the Fresnel equations. © 2006.

DOI： 10.1016/j.tsf.2006.10.090

Patterned hydrophobic-hydrophilic templates made from microwave-plasma enhanced chemical vapor deposited thin films

Wu Y., Kouno M., Saito N., Andrei Nae F., Inoue Y., Takai O.

Thin Solid Films Vol. 515 ( 9 ) page： 4203 - 4208 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

In the present research, nano-structured materials exhibiting super-hydrophobic behavior obtained by microwave-plasma enhanced chemical vapor deposition (MPECVD) had their surface chemical status altered through vacuum ultraviolet (VUV) light irradiation. Falling water droplets rolled and bounced without wetting or spreading over the initially super-hydrophobic surfaces. We demonstrate a surface preparation technique to create a patterned super-hydrophobic/super-hydrophilic substrate in which micropatterns with super-hydrophobic and super-hydrophilic regions were prepared through irradiation with VUV light. To confirm the method, growth of water droplets is observed in situ on such super-hydrophobic/super-hydrophilic micropatterns. We discuss the applicability of the super-hydrophobic/super-hydrophilic pattern to the bottom-up assembling of materials, like site-selective electroless Cu plating on patterned substrates made of paper and selective cell culture experiments. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.02.065

The importance of precursor molecules symmetry in the formation of self-assembled monolayers

Lee S.H., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 46 ( 3 A ) page： 1118 - 1123 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We investigated the role of precursors molecular symmetry in the self-assembled formation of organosilane monolayer by applying atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD), Fourier transform infrared spectroscopy (FT-IR) and contact angle measurement. Octadencyltrichlorosilane (OTS), octadecylmethydichlorosilane (ODCS), and octadecyldimethylchlorosilane (ODMS) were used as raw materials to form organosilane monolayers. The organosilane monolayers were prepared by a liquid phase method at a reaction temperature of 5°C and an humidity in reactor of 50%. AFM observations suggested that only OTS molecules grew two-dimensionally on the Si substrate surface. In GIXD results showed these OTS molecules to be arranged in a crystalline state on the Si surface. Thus "self- organization" occurred during OTS monolayer formation process. However, in the case of ODCS and ODMS, the monolayers formed were in an amorphous state. In addition, FT-IR and water contact angle measurement indicated that the packing density of the OTS monolayer was higher than that of the ODCS and ODMS monolayers. Only when the precursor molecules had an axis where the silanol groups were in three-fold did "self-organization" occurs in the formation of the organosiloxane monolayer. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.1118

A micropatterned multifunctional carbohydrate display by an orthogonal self-assembling strategy

Sato H., Miura Y., Saito N., Kobayashi K., Takai O.

Biomacromolecules Vol. 8 ( 2 ) page： 753 - 756 2007.2

Fabrication and characterization of ultra-water-repellent alumina-silica composite films

Ishizaki T., Saito N., Inoue Y., Bekke M., Takai O.

Journal of Physics D: Applied Physics Vol. 40 ( 1 ) page： 192 - 197 2007.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150°, whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica-alumina system. © 2007 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/40/1/014

Behavior of various organosilicon molecules in PECVD processes for hydrocarbon-doped silicon oxide films

Yun Y., Yoshida T., Shimazu N., Inoue Y., Saito N., Takai O.

Solid State Phenomena Vol. 124-126 ( PART 1 ) page： 347 - 350 2007

Language：English Publishing type：Research paper (scientific journal) Publisher：Solid State Phenomena

Plasma diagnosis was performed by means of optical emission spectroscopy in the plasma-enhanced chemical vapor deposition process for preparation of hydrocarbon-doped silicon oxide films. The chemical bonding states were characterized by a fourier-transform infrared spectrometer. Based on the results of the diagnosis in organosilane plasma and the chemical bonding states, a reaction model for the formation process of hydrocarbon-doped silicon oxide films was discussed. From the results of optical emission spectroscopy, we found that the oxygen atoms of methoxy groups in TMMOS molecules can be dissociated easily in the plasma and behave as a kind of oxidizing agent. Siloxane bondings in HMDSO, on the other hand, hardly expel oxygen atoms.

DOI： 10.4028/3-908451-31-0.347

Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis

Bratescu M., Suda Y., Sakai Y., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 4 ) page： 1314 - 1319 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

The role of carbon atoms in a dc plasma-enhanced chemical vapor deposition for carbon nanotubes (CNTs) synthesis was investigated. It was observed that at 1.33 kPa pressure of CH4 gas in plasma, a high value of the ratio between the intensities of the graphite peak (G peak) and the disorder peak (D peak) in the Raman spectrum corresponds to the maximum value of the excited C number density in the vicinity of the Si substrate. It was found that a CH4 gas pressure higher than 1.33 kPa leads to an increase of the relative density of the C2, C3 molecules and the clusters, and to a decrease of the C excited atom number density in plasma. The presence of a high amount of sp2-graphite in the composition of CNTs observed in Raman spectrum was also confirmed by the measurement of the IR-active G peak at 1584 cm- 1 in the transmission spectrum. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.03.022

Degradation of bacteria using pulse plasma discharge in liquid medium

Baroch P., Takeda T., Oda M., Saito N., Takai O.

Conference Record of the International Power Modulator Symposium and High Voltage Workshop page： 482 - 485 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the International Power Modulator Symposium and High Voltage Workshop

The paper reports on the study of an underwater electrical pulse plasma discharge operating under relatively low discharge voltages (below 1 kV) and its utilization for degradation of bacteria contained in the liquid medium. For this purpose, a system based on wire-to-wire electrode configuration was designed. Results show the ability of the system to generate active species, observed by optical emission spectroscopy and also revealed from the change in pH of treated solution. Effective generation of these species then results in a relatively fast decomposition rate of tested organic dyes. Consequent treatment process with two types of bacteria alsoexhibits positive results showing successful and very fast decrease in bacteria population. ©2006 IEEE.

DOI： 10.1109/MODSYM.2006.365289

Multifunctional micropatterning of glycoconjugate polymer via a orthogonal self-assembly

Miura Y., Sato H., Kobayashi K., Saito N., Takai O.

Polymer Preprints, Japan Vol. 55 ( 2 ) page： 5260 - 5261 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

We propose a novel strategy for a multiple micropatterned display of carbohydrates by orthogonal supramolecular formation. Two kinds of glycopolymer was self-assembled on the substrate by hydrophobic and electrostatic interaction. Two types of protein and cell was adsorbed on the glycopolymer due to the molecular recognition.

Rapid mass production of gold nanoaprticle from gold salts

Yonezawa T., Oda M., Ishizaki T., Saito N., Takai O.

Polymer Preprints, Japan Vol. 55 ( 2 ) page： 3843 - 3844 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

A novel rapid mass production process of gold nanoparticles by using spark discharge in solution is proposed in this study. Into AuCl4- aqueous solution, gelatin was introduced as the stabilizing reagent. Then, spark discharge at ca. 800 V was applied. The yellow solution turned into dark-red, which suggests the formation of gold nanoparticles protected by gelatin. UV-Vis spectra of the obtained dispersions indicates the complete reduction of Au3+ ions and production of gold nanoparticles. The TEM images revealed that gold nanoparticles were dispersed independently without aggregation. This process is quite unique and easy for mass production of various kinds of metal nanoparticles.

Study of alkyl organic monolayers with different molecular chain lengths directly attached to silicon

Ishizaki T., Saito N., SunHyung L., Ishida K., Takai O.

Langmuir Vol. 22 ( 24 ) page： 9962 - 9966 2006.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

Alkyl organic monolayers with different alkyl molecular chain lengths directly attached to silicon were prepared at 160°C from 1-decene (C10), 1-dodecene (C12), 1-tetradecene (C14), 1-hexadecene (C16), and 1-octadecene (C18). These monolayers were characterized on the basis of water contact angle measurement, ellipsometry, X-ray reflectivity (XR), X-ray photoelectron spectroscopy (XPS), and grazing incidence X-ray diffraction (GIXD) to elucidate the effect of the molecular chain length on the molecular arrangement and packing density of the monolayers. Water contact angle and XPS measurements showed that C12, C14, and C16 monolayers have a comparably higher quality, while the quality of C10 and C18 monolayers is worse. GIXD revealed that the alkyl monolayers directly attached to the Si were all amorphously structured regardless of their alkyl chain length. The amorphous structure of the alkyl monolayers could be attributed to the rigid Si-C bonding, low quality of hydrogen-terminated silicon substrate, and/or low mobility of physisorbed molecules. © 2006 American Chemical Society.

DOI： 10.1021/la052342u

Treatment of immobilized collagen on poly(tetrafluoroethylene) nanoporous membrane with plasma

Bratescu M.A., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 45 ( 10 B ) page： 8352 - 8357 2006.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

In this work we treated type I collagen immobilized on different nanoporous membranes with microwave (MW) argon plasma. Hydrophobic and hydrophilic nanoporous substrates of poly(tetrafluoroethylene), with thickness varying from 35 to 70 μm and a 100nm pore size, were employed as support for collagen immobilization. On the hydrophilic nanoporous membrane, after the MW plasma treatment, the immobilized collagen changed its morphology and showed a tendency to self-assemble in quasi-regular forms as microellipsoids. The presence of collagen immobilized on the nanoporous membrane after the MW plasma treatment was analyzed by detecting in the Raman spectrum an α-helix form, NH deformation vibration, amide II band at .1550 cm-1, a characteristic group frequency of the collagen macromolecule. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.8352

Water droplets interaction with super-hydrophobic surfaces

Wu Y., Saito N., Nae F.A., Inoue Y., Takai O.

Surface Science Vol. 600 ( 18 ) page： 3710 - 3714 2006.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Static and dynamic behavior of water droplets on various super-hydrophobic (SH) surfaces were investigated. First, SH plant leaves were used as samples and we found out that surface nanostructure has a great influence on the droplets dynamic behavior. Then, we made biomimetic structures by depositing SH films through microwave-plasma enhanced chemical vapor deposition (MPECVD). Next, SH surfaces were fabricated by covering previously roughened SiOx films with self-assembled monolayers (SAMs). The substrates were then charged with static electricity, and water droplets falling on tilted charged surfaces leaped up or run uphill at high speeds, proving that not only the surface nanostructure but also its chemical endgroups have a great effect on the water droplets motion on SH surfaces. © 2006.

DOI： 10.1016/j.susc.2006.01.073

Depth profiles of the Fermi level at an amorphous-carbon nitride/SiO<inf>2</inf>/n-type-Si heterojunction interface obtained by Kelvin probe force microscopy

Ishizaki T., Saito N., Ohta R., Takai O.

Diamond and Related Materials Vol. 15 ( 9 ) page： 1378 - 1382 2006.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Diamond and Related Materials

To explore the work function of a typical amorphous-CN film containing a nitrogen concentration of 23.5 at.%, surface potential images were acquired using Kelvin probe force microscopy. Based on the Fermi level of the n-type Si and the contact potential difference between the amorphous-CN film and the n-Si substrate, the work function of the amorphous-CN film was estimated to be 5.2 ± 0.2 eV below its vacuum level. Using the surface potential depth profile for an etched amorphous-CN film, energy diagrams of the amorphous-CN/SiO2/n-Si interface were constructed based on the positional relationship of the Fermi level. These band diagrams showed that band bending occurred at the amorphous-CN/SiO2/n-Si interface despite the Fermi level pinning effect of surface trapping due to the SiO2 insulator layer. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2005.10.001

Synthesis of DLC films by PECVD combined with hollow cathode sputtering

Anita V., Butsuda T., Saito N., Takai O.

Vacuum Vol. 80 ( 7 SPEC. ISS. ) page： 736 - 739 2006.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Vacuum

The mechanical and electrical properties of aluminium-doped diamond-like carbon (DLC) thin films obtained with a hybrid method combining hollow magnetron discharge sputtering and plasma-enhanced chemical vapour deposition (PECVD) are reported. The ratio between the mass flows of methane reactive gas and argon inert gas was found to have a big influence on the properties of doped DLC films. For low mass flow of methane gas the cathode surface was kept in a metallic state. By increasing methane mass flow the cathode surface became to be covered with DLC and the behaviour of the discharge changed, influencing the properties of deposited films. The lowest resistivity (10-4 Ω cm) of thin films was obtained in the metallic state of the cathode but without DLC character, as indicated by Raman measurements. The resistivity increased in the intermediate mode (0.01 Ω cm) and attained higher value (1 Ω cm) in the poisoned state of the cathode. These films presented DLC character, with D and G bands, as revealed by Raman measurements. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2005.11.020

Synthesis of nitrogen-rich carbon nitride thin films via magnetic field-assisted inductively coupled plasma sputtering

Ohta R., Yokota T., Anita V., Saito N., Takai O.

Vacuum Vol. 80 ( 7 SPEC. ISS. ) page： 752 - 755 2006.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Vacuum

Carbon nitride (CNx) thin films were synthesized by magnetic field-assisted inductively coupled plasma (ICP) sputtering. The electron density, electron temperature and optical emission intensity of the plasma state were significantly changed by varying the external magnetic field applied. The CNx thin film with the highest nitrogen content (N/C=1.16) was obtained when the electron density was at its highest and the electron temperature at its lowest. Additionally, the optical emission from atomic nitrogen was the strongest under the same condition. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2005.11.042

Magnetron plasma-enhanced chemical vapor deposition of diamond-like carbon thin films

Anita V., Saito N., Takai O.

Thin Solid Films Vol. 506-507 page： 63 - 67 2006.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

An RF magnetron plasma-enhanced chemical vapor deposition system with variable magnetic field (MagPECVD) was utilized for high rate deposition of diamond-like carbon thin films. Deposition rate was nonuniform, with minimum value of 30 nm/min in the center of the cathode where the low ionic flux is determined by the absence of the E × B electronic drift. The highest value of 1029 nm/min was registered in the position of the cathode with the highest ion flux determined by the presence of the E × B electronic drift. Hardness, elastic modulus and RMS roughness of thin films were dependent on local values of magnetic field intensities and the values of input power. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.08.074

Microarc plasma treatment of titanium and aluminum surfaces in electrolytes

Anita V., Saito N., Takai O.

Thin Solid Films Vol. 506-507 page： 364 - 368 2006.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

The advanced plasma process of microarc treatment in electrolytes was utilized to prepare oxide layers on aluminum and titanium substrates by anodic conversion. This paper reports results on morphology, structure, growth rates, hardness and water contact angle measurements of titanium and aluminum oxidized surfaces obtained by microarc discharge in ecologically clean and safe electrolytes. Porous oxide layers were formed on the sample surface after the microarc treatment. The morphology of surfaces was dependent on the current intensity during the treatment. The pore diameter in the films decreased with the increase in current intensity and the thickness of the oxide film increased almost linearly with the time of treatment for a constant input power. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.08.083

Visualization of human plasma fibrinogen adsorbed on highly oriented pyrolytic graphite by scanning probe microscopy

Ohta R., Saito N., Ishizaki T., Takai O.

Surface Science Vol. 600 ( 8 ) page： 1674 - 1678 2006.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Human plasma fibrinogen (HPF) was observed by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) conducted in non-contact mode. The HPF was adsorbed on a highly oriented pyrolytic graphite (HOPG) substrate as single molecules, as aggregated bundles, and as aggregated fibers. Topographic and phase images confirmed structural changes in the HPF after exposure to air, while topographic and KPFM images confirmed fibers with the width of a single HPF molecule. Additionally, KPFM confirmed the surface potential difference between the HPF and the HOPG, and periodical potential drop reflecting the E and D domains in the fiber. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2005.12.058

Carbohydrate Microarrays by Click Chemistry

H. Sato, Y. Miura, T. Yamauchi, N. Saito, K. Kobayashi, O. Takai

Trans. Mater. Research. Soc. J. Vol. 31 page： 659-703 2006

Micropatterned saccharide display on the silicon surface

Sato H., Miura Y., Saito N., Kobayashi K., Takai O.

Polymer Preprints, Japan Vol. 54 ( 1 ) 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

The immobilization and the micro-patterning of biomolecules on the solid surfaces are paid much attention for the application of biomaterials, and biosensors. Micro-patterned carbohydrates on solid surfaces are useful to analyze carbohydrate-protein interactions and to fabricate the scaffolds of cell cultivation. We have proposed a new method for micro-patterned carbohydrate display. The micropattern composed of hydrophobic and electrostatically positive regions were fabricated by methyl and amino terminated self-assembled monolayers (SAM). The patterned substrates were incubated in two types of aqueous solutions of PVLA and Heparin, in this order. The PVLA and Heparin site-selectively adsorbed on methyl and amino terminated SAMs, respectively. It indicated that the two dimensional matrix of PVLA and Heparin can be fabricated on the micro-patterned substrate. The micropatterning of two different components on one substrate enables two different biomacromolecules to be self-assembled into micro pattern.

Photolithographic patterning of dendrimer monolayers and pattern-selective adsorption of linear macromolecules

Yamazaki T., Imae T., Sugimura H., Saito N., Hayashi K., Takai O.

Journal of Nanoscience and Nanotechnology Vol. 5 ( 11 ) page： 1792 - 1800 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology

Alkyl groups of n-octadecyltrimethoxysilane (ODS) in a self-assembled monolayer on a silicon substrate were oxidized to carboxyl groups by partial irradiation of vacuum ultra-violet light under the photomask, producing a COOH/ODS line pattern. After active esterification of carboxyl groups, two kinds of amine-terminated dendrimers, poly(propyleneimine) and poly(amido amine) (PAMAM) dendrimers, were immobilized on a COOH line through amide-bond so that photolithographic dendrimer/ODS pattern was finally fabricated. Preparation was certified by atomic force microscopy (AFM) and surface-enhanced infrared absorption spectroscopy at transmission mode. Adsorption of linear macromolecutes was examined on PAMAM dendrimer/ODS pattern. After adsorption of poly-L-glutamic acid (PGA) at a pH below α-helix-random coil transition, rod-shape texture was observed only on the dendrimer line in an AFM image. This texture is an aggregate of α-helical PGA. Sodium hyaluronate and DNA were also adsorbed selectively on the dendrimer line, keeping the line profile, although characteristic textures were not observed. Copyright © 2005 American Scientific Publishers All rights reserved.

DOI： 10.1166/jnn.2005.434

Properties of DLC thin films produced by RF PE-CVD from pyrrole monomer

Takai O., Anita V., Saito N.

Surface and Coatings Technology Vol. 200 ( 1-4 SPEC. ISS. ) page： 1106 - 1109 2005.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

This paper reports the properties of diamond like carbon (DLC) thin films obtained in a capacitively coupled, RF powered, plasma enhanced chemical vapor deposition (PE-CVD) system. A precursor used was pyrrole, one of the most known monomers for conductive polypyrrole polymer processing. The deposition rate of thin films was high: 74 nm/min at 50 W and 425 nm/min at 400 W input power. The hardness and elastic modulus of thin films reached the highest values of 16.5 and 148 GPa at 400 W and the surface morphology of the films did not suffer important changes in the interval of utilized input powers: RMS roughness decreased from 0.45 nm at 50 W to 0.20 nm at 400 W. All deposited films were transparent in the infrared range. Raman measurements revealed that the increase of the input power led to a decrease of the sp3 and an increase of sp2 bonded carbon atoms in thin films. The resistivity of DLC thin films was very high for low values of RF input power (ρ> 107 kΩ cm) and decreased at higher values of input power (ρ≈ 55 kΩ cm at 400 W). By using nitrogen as a doping element the resistivity decreased to ρ ≈ 3.5 kΩ cm at 400 W and 20 sccm N2. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2005.02.024

Surface-potential reversibility of an amino-terminated self-assembled monolayer based on nanoprobe chemistry

Saito N., Lee S., Takahiro I., Hieda J., Sugimura H., Takai O.

Journal of Physical Chemistry B Vol. 109 ( 23 ) page： 11602 - 11605 2005.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Nanoprobe chemistry offers a promising approach for the construction of nanostructures consisting of organic molecules by employing the tip of a scanning probe microscope. In a previous report, we demonstrated that a nitroso-terminated surface on an organosilane self-assembled monolayer could be converted into an amino-terminated surface by applying such a nanoprobe electrochemical technique. This paper reports on surface-potential reversibility originating from a reversible chemical reaction between amino and nitroso groups. In addition, we demonstrate surface-potential memory based on this chemical reversibility. Ammo-terminated SAMs were prepared from p-aminophenyl-trimethoxysilane through chemical vapor deposition. Surface potentials were acquired by Kelvin force microscopy. When scanning probe lithography was conducted with a gold tip at positive-bias voltages, the surface potential of the scanned area shifted dramatically in the negative direction. Scanning with negative-bias voltages led to positive shift in the surface potential of the scanned area. The surface potential could be recovered even after multiple scannings with positive and negative applied bias voltages. On the basis of this discovery, we also succeeded in demonstrating surface-potential memory via our nanoprobe electrochemical technique. © 2005 American Chemical Society.

DOI： 10.1021/jp044943k

An investigation into the effect of ionic species on the formation of ZnTe from a citric acid electrolyte

Ishizaki T., Saito N., Takai O., Asakura S., Goto K., Fuwa A.

Electrochimica Acta Vol. 50 ( 16-17 ) page： 3509 - 3516 2005.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

Cathodic electrodeposition of ZnTe film was carried out on Au/Cu substrate using three kinds of citric acid electrolytes, each with a different counter anion, i.e., sulfate, chloride, or nitrate ions, to investigate the anion species' influence on the morphology, composition and structure of the resulting electrodeposited ZnTe films. Both chloride and nitrate electrolytes gave crystalline ZnTe films with almost stoichiometric ZnTe composition under electrolytic conditions similar to those optimized previously for sulfate electrolyte. The mean crystallite size of the electrodeposited ZnTe films ranged from 13 to 37 nm. The effect of the ionic species on the crystallite size was also investigated. The degree of ZnTe(1 1 1) plane orientation of the films obtained from nitrate electrolyte was stronger than that of the films from sulfate or chloride electrolytes. High resolution SEM observations revealed different morphologies depending on the anion in the electrolytic solution. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2004.12.028

Fabrication of ferroelectric self-assembled fluorinated polyether monolayer on hydrogen-terminated Si(111) surface

Okano T., Inari H., Ishizaki T., Saito N., Sakamoto W., Takai O.

Chemistry Letters Vol. 34 ( 4 ) page： 600 - 601 2005.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemistry Letters

Covalently bonded ferroelectric self-assembled monolayers on silicon surface were fabricated via hydrosilylation of terminally allylated and propargylated fluorine-containing polyether adsorbates on hydrogen-terminated Si(111) substrates. Incomplete polarization - electric field loops indicating ferroelectric property were observed in a range of bias voltage ±300 mV. Copyright © 2005 The Chemical Society of Japan.

DOI： 10.1246/cl.2005.600

High-resolution submicron patterning of self-assembled monolayers using a molecular fluorine laser at 157 nm

Nae F.A., Saito N., Hozumi A., Takai O.

Langmuir Vol. 21 ( 4 ) page： 1398 - 1402 2005.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

Using a molecular fluorine laser at 157 nm wavelength, submicron patterning of organosilane self-assembled monolayers (SAMs) is demonstrated utilizing mask-contact photolithography. An organosilane, namely, octadecyltrimethoxysilane [ODS, CH3(CH2) 17Si(OCH3)3], SAM is chemisorbed onto Si substrates covered with a 2 nm thick oxide layer and subsequently patterned using the laser. The optical path of the laser beam and the photomask-sample space are evacuated and then backfilled and purged with nitrogen during laser firing. The resulting pattern is investigated using various measurement techniques. The scanning probe microscopy images show that patterns are transferred to the SAM-covered Si substrates and that 500 nm features are successfully photoprinted in this way.

DOI： 10.1021/la0480944

Fabrication of a built-in patterned metal microstructure on a polymer substrate using a microstructured organic monolayer template

Saito N., Hieda J., Takai O.

Electrochemical and Solid-State Letters Vol. 7 ( 12 ) 2004.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochemical and Solid-State Letters

We have successfully developed a novel route based on nanoimprinting lithography. In developing our approach, we demonstrated that metal on an organic monolayer could be easily transferred to a polymer surface by nanoimprinting lithography, and that patterned metal fabricated in this manner would bind strongly to the polymer substrates. © 2004 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1819870

Effect of N doping on properties of diamond-like carbon thin films produced by RF capacitively coupled chemical vapor deposition from different precursors

Anita V., Butuda T., Maeda T., Takizawa K., Saito N., Takai O.

Diamond and Related Materials Vol. 13 ( 11-12 ) page： 1993 - 1996 2004.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Diamond and Related Materials

In this paper, we report results concerning properties of diamond-like carbon (DLC) thin films obtained in different experimental conditions: various RF power values, and different precursors (methane, acetone and toluene or in combination with nitrogen). The deposition rate of DLC thin films obtained from precursors with low ionizing energy and high number of carbon atoms in molecule as acetone and toluene was higher (142 nm/min for acetone and 607 nm/min for toluene as compared with 79 nm/min for methane at 400 W input power). The highest value of hardness was obtained from methane (18 GPa). In the case of acetone and toluene precursors, the hardness increased with input power to the highest values of 16.8 and 14.8 GPa. By utilizing nitrogen as doping element, the resistivity of DLC thin films obtained from methane and acetone decreased from values higher than 107 Ω cm to lower values of 12.5 × 103 Ω cm for 3.79% nitrogen atomic concentration in the case of films obtained from methane and 40 × 103 Ω cm for 4.26% nitrogen atomic concentration in the case of films obtained from acetone. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2004.05.002

Reversible nanochemical conversion

Sugimura H., Lee S., Saito N., Takai O.

Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures Vol. 22 ( 6 ) 2004.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures

Local chemical conversion of an organic surface that consists of a surface-confined monolayer is demonstrated in a reversible manner based on electrochemical reactions induced beneath a conductive probe tip of an atomic force microscope. The monolayer was prepared by a self-assembling technique from the precursor, p-aminophenyltrimethoxysilane. The chemical state of this self-assembled monolayer was regulated by probe-tip scanning with a bias voltage applied between the tip and substrate. With a positive substrate bias scanning, the monolayer surface was oxidized to be nitroso-terminated. With a negative bias scanning, this monolayer could be amino-terminated. These oxidation and reduction processes could be reversibly repeated. © 2004 American Vacuum Society.

DOI： 10.1116/1.1825020

Contribution of primary chemical bonding states of amorphous carbon nitride to hardness

Saito N., Ohta R., Lee K.H., Kobayashi Y., Okazaki S., Inoue Y., Sugimura H., Takai O.

Electrochemical and Solid-State Letters Vol. 7 ( 8 ) 2004.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochemical and Solid-State Letters

The hardness of amorphous carbon nitride (CN) was investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results of NMR measurements showed that sp2 and/or sp hybrid orbitals controlled the hardness of amorphous-CN films, which had been determined by nanoindentation tests. The intensity of the C-H and CN stretching modes observed in the FTIR spectra was the weakest in the hardest sample. The decreases of -CH3 and -CH2 groups indicated that the amorphous network had increased. The sp2 hybrid orbital forms a cross-linker which plays an important role in improving of the hardness of the film. © 2004 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1763791

Organosilane self-assembled monolayers directly linked to the diamond surfaces

Ohta R., Saito N., Inoue Y., Sugimura H., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 5 ) page： 2005 - 2009 2004.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The organosilane self-assembled monolayers (SAM) which were linked to diamond surfaces were investigated. It was observed that the SAM were prepared from p-aminophenyltrimethoxysilane (H2N(CH)6Si(OCH 3)3, APhS) on diamond substrates and were irradiated by vacuum ultraviolet (VUV) light. It was also observed that the thickness of the SiOx layer was increased by the APhS-SAM formations and VUV irradiations. It was found that the APhS-SAM/ nano-scale SiOx/ diamond could be used for diamond-bio hybridized devices.

DOI： 10.1116/1.1776184

Fabrication of piezoelectric self-assembled fluorinated polyether monolayer on hydrogen-terminated Si(111) surface.

Okano, T; Inari, H; Saito, N; Takai, O

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 228 page： U471 - U471 2004.8

Photochemical reaction of organosilane self-assembled monolayer as studied by scanning probe microscopy

Sugimura H., Saito N., Ishida Y., Ikeda I., Hayashi K., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 4 ) page： 1428 - 1432 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The study of a patterning process of an alkylsilane self-assembled monolayer (SAM) using vacuum ultraviolet (VUV) light at 172 nm, by charaterizing the VUV-irradiated SAM surfaces through lateral force microscopy (LFM) and Kelvin force microscopy (KFM), was presented. The relative frictional forces and surface potentials of the VUV-irradiated regions at various irradiation dose rates were measured by LFM and KFM. VUV-irrated SAMs showed particularly lower surface potentials than the other SAM surface potentials than the other SAM surfaces with different dose rates, at a certain dose rate of 10-15 J/cm 2. It was observed that LFM and KFM measurements were promising in order to probe chemistries on organic thin films proceeding.

DOI： 10.1116/1.1764818

Exploration of the chemical bonding forms of alkoxy-type organic monolayers directly attached to silicon

Saito N., Lee S., Maeda N., Ohta R., Sugimura H., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 4 ) page： 1425 - 1427 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The preparation of alkoxy-type organic monolayers on hydrogen-terminated silicon from 1-undecanol (UN), 1-nonanol (NO), 1-heptanol (HP) and 4-phenylphenenol (PP) was discussed. The characterization of these monolayers was based on X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). A SiOx peak was clearly observed for the HP, NO and PP monolayers. It was shown that the generation of SiO x in the PP monolayer was due to steric hindrance of the aromatic rings. It was found that the the -CH2-region in the FT-IR spectra showed that the shorter alkyl chains promoted the formation of gauche conformers in the monolayers.

DOI： 10.1116/1.1759353

Generation of amino-terminated surfaces by chemical lithography using atomic force microscopy

Saito, N; Maeda, N; Sugimura, H; Takai, O

LANGMUIR Vol. 20 ( 13 ) page： 5182 - 5184 2004.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

Self-assembled monolayers (SAMs) covered with nitroso end groups were reduced using an atomic force microscope. As the bias voltage become more negative (beyond -4 V), the surface potential of the scanned area become closer to that of the amino-terminated SAM. Following this chemical change, however, no change in topographic features was detected, implying retained stability of the underlying SAM layer. We then released carboxylate-modified polystyrene (PS) spheres into a pH 4 solution containing the sample. Subsequent imaging with atomic force microscopy (AFM) revealed that these PS spheres were only selectively immobilized on the regions that were originally scanned at -6 V to form amino termination. In summary, using AFM set to a specific voltage, we were able to selectively generate micropatterned regions of the SAM with amino termination.

DOI： 10.1021/la0353428

UV Raman spectroscopic probing into nitrogen-doped hydrogenated amorphous carbon

Ohta R., Saito N., Okazaki S., Inoue Y., Sugimura H., Takai O.

Thin Solid Films Vol. 457 ( 1 ) page： 128 - 132 2004.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

From the viewpoint of hardness, chemical bonding states of nitrogen-doped hydrogenated amorphous carbon film were characterized by Ultra violet (UV) Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. UV Raman spectra revealed that disorder of the structure in nitrogen-doped hydrogenated amorphous carbon was promoted by applying higher bias voltages in the preparation. FT-IR spectra showed that N-H bonds decreased and sp 3C-sp3N bonds increased with the increase of the bias voltages. The content of sp3C-sp3N bonds was maximized at the bias voltage of -800 V. We found out a guarantee that the content of sp 3C-sp3N bonds against bias voltages correlated with the hardness obtained by nanoindentation test. The structural disorder and the increase of sp3C-sp3N bonds are possible source of the hardness in the case of nitrogen-doped hydrogenated amorphous carbon. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2003.12.049

Electrodeposition of CuInTe<inf>2</inf> film from an acidic solution

Ishizaki T., Saito N., Fuwa A.

Surface and Coatings Technology Vol. 182 ( 2-3 ) page： 156 - 160 2004.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

Copper-indium-telluride films were electrochemically deposited from solutions containing CuCl2, InCl3, TeO2 and HCl. Although a flat and smooth film with closely stoichiometric composition was deposited at -660 mV vs. Ag/AgCl at 303 K from a solution of 2.5×10-4 mol dm-3 CuCl2, 1.0×10-2 mol dm-3 InCl3, 5.0×10-4 mol dm-3 TeO2 and 0.1 mol dm-3 HCl, a polycrystalline CuInTe2 film was not obtained. Increasing the temperature from 303 to 363 K allowed the deposition at lower overpotential of a polycrystalline CuInTe2 film with closely stoichiometric composition and increased indium content. The band gap of the polycrystalline CuInTe2 film electrodeposited at 363 K at -660 mV was 0.98 eV. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2003.07.004

Surface potential microscopy for chemistry of organic self-assembled monolayers in small domains

Sugimura H., Saito N., Maeda N., Ikeda I., Ishida Y., Hayashi K., Hong L., Takai O.

Nanotechnology Vol. 15 ( 2 ) 2004.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

Micropatterning techniques using vacuum ultra-violet light at 172 nm in wavelength and an ultra-violet laser at 244 nm were applied to organosilane self-assembled monolayers (SAMs) formed on Si substrates covered with a 2 nm thick oxide layer. These SAMs were prepared from precursors, that is, octadecyltrimethoxysilane (ODS) or p-chloromethylphenyltrimethoxysilane (CMPhS). Polar functional groups such as COOH were generated through photochemical oxidation of the SAMs. Furthermore, the SAMs were Simultaneously etched and finally removed from the photoirradiated area. Surface potentials of the photoirradiated areas at various irradiation dose rates were measured by Kelvin-probe force microscopy (KFM) using the unirradiated area on each of the photopatterned samples as a reference. Changes in the surface chemical composition of the SAMs could be clearly and sensitively measured by KFM through the difference in surface potential between the irradiated and unirradiated SAMs.

DOI： 10.1088/0957-4484/15/2/015

Oxygen gas assisted electron beam lithography in organosilane self-assembled monolayers

Yamaguchi M., Saito N., Takai O.

Digest of Papers - Microprocesses and Nanotechnology 2004 page： 198 - 199 2004

Microstructured π-conjugated organic monolayer covalently attached to silicon

Saito N., Hayashi K., Sugimura H., Takai O.

Langmuir Vol. 19 ( 26 ) page： 10632 - 10634 2003.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

A phenylacetylene (PA) monolayer was prepared on hydrogen-terminated silicon. Through vacuum ultraviolet (VUV) lithography, micropatterned PA-monolayer/SiO2 samples were subsequently fabricated. The surface potential and electrical conductivity of the microstructured PA monolayers were examined by Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), respectively. KPFM measurements showed that the PA-monolayer surface regions were negatively charged. C-AFM measurements demonstrated that, in the microdomains, the PA-monolayer regions had a higher conductivity than the SiO2 regions fabricated by VUV lithography. This is the first report of electronic property images of a monolayer directly attached to silicon being demonstrated in microregions.

DOI： 10.1021/la034187u

Origin of N 1s spectrum in amorphous carbon nitride obtained by X-ray photoelectron spectroscopy

Ohta R., Lee K.H., Saito N., Inoue Y., Sugimura H., Takai O.

Thin Solid Films Vol. 434 ( 1-2 ) page： 296 - 302 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

This paper focuses on determining a reasonable peak assignment for the N 1s spectrum of amorphous carbon nitride (a-CN) measured by X-ray photoelectron spectroscopy (XPS). Unfortunately, several peaks of a-CN have not been identified, that is, there has yet to be any shared understanding of their chemical bonding states. We investigated this by monitoring changes in spectra before and after vacuum ultraviolet (VUV) irradiation, thus obtaining information about the changes of chemical bonds. The observed changes were discussed based on the chemical shifts of components of a-CN determined from ab-initio molecular orbital (MO) calculations. We have proposed the following peak assignment for N 1s. The peaks located at approximately (1) 397.6, (2) 398.2, (3) 399.0, (4) 400.0, (5) 400.9 and (6) 401.9 eV were assigned to the chemical bonding states of (1) β-C 3 N 4 , (2) pyridine, (3) formonitril, (4) methylmethyleneamine, (5) pyrido[2,1,6-de]quinolizine, and (6) a nitroso group. This assignment did not agree with oft-quoted ones. However, only this peak assignment provides a reasonable interpretation for the changes we observed in a-CN introduced by VUV irradiation, and allows us to understand the chemical bonding states of a-CN film. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(03)00457-7

Selective immobilization of functional organic molecules onto a microtemplate fabricated using an amino-terminated self-assembled monolayer

Hayashi K., Hozumi A., Saito N., Sugimura H., Takai O.

Surface Science Vol. 532-535 page： 1072 - 1078 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Micropatterned amino-terminated self-assembled monolayers (SAMs) were applied as templates to promote selective chemical reactions in minute spatial scale. The surface charge properties of the SAMs were investigated through zeta-potential measurements conducted in solutions of various pH values. These SAMs were then utilized in order to selectively immobilize carboxylate-modified fluorescence spheres (CM-FluoSpheres) on the sample surface. Each SAM was uniformly formed onto a clean Si(1 0 0) substrate covered with a thin oxide layer (SiO2) by chemical vapor deposition using n-(6-aminohexyl)aminopropyltrimethoxysilane [AHAPS:H2N(CH2)6NH(CH2)3S i(OCH3)3] as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures consisting of AHAPS-SAM and SiO2 were fabricated. The micropatterned AHAPS-SAM/SiO2 samples were then immersed in a solution dispersed with CM-FluoSpheres. The solution was adjusted to pH = 2, 6 or 8. At pH = 8, the CM-FluoSpheres did not adsorb on the micropatterned AHAPS-SAM/SiO2. At pH = 2 and 6, the CM-FluoSpheres adsorbed specifically on the regions covered with AHAPS-SAM. In particular, the adsorption behavior at pH = 6 was highly selective. These results were predictable considering the isoelectric points of AHAPS-SAM and SiO2, that is, pH = 7.5 and 2.0, respectively. At pH = 6, the SiO2 surface was negatively charged while the AHAPS-SAM surface was positive. Since the CM-FluoSpheres, which are terminated with carboxyl groups, were negatively charged at this pH value, the SiO2 and AHAPS-SAM surfaces had repulsive and attractive interactions, respectively, with the CM-FluoSpheres. These opposite electrostatic interactions were the origin of the complete selectivity achieved in the adsorption. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00211-5

Chemical resistivity of self-assembled monolayer covalently attached to silicon substrate to hydrofluoric acid and ammonium fluoride

Saito N., Youda S., Hayashi K., Sugimura H., Takai O.

Surface Science Vol. 532-535 page： 970 - 975 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Self-assembled monolayers (SAMs) were prepared on hydrogen-terminated silicon substrates through chemical vapor deposition using 1-hexadecene (HD) as a precursor. The HD-SAMs prepared in an atmosphere under a reduced pressure (≈50 Pa) showed better chemical resistivities to hydrofluoric acid and ammonium fluoride (NH4F) solutions than that of an organosilane SAM formed on oxide-covered silicon substrates. The surface covered with the HD-SAM was micro-patterned by vacuum ultraviolet photolithography and consequently divided into two areas terminated with HD-SAM or silicon dioxide. This micro-patterned sample was immersed in a 40 vol.% NH4F aqueous solution. Surface images obtained by an optical microscopy clearly show that the micro-patterns of HD-SAM/silicon dioxide were successfully transferred into the silicon substrate. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00158-4

Micropatterned 1-alkene self-assembled monolayer on hydrogen-terminated silicon by vacuum ultraviolet lithography

Saito N., Kadoya Y., Hayashi K., Sugimura H., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 42 ( 4 B ) page： 2534 - 2537 2003.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We fabricated micropatterned 1-alkene self-assembled monolayers (SAMs) on p-type Si(111). 1-Alkene SAMs were prepared from 1-hexadecene (HD) and 1-octadecene (OD) through reduced pressure chemical vapor deposition. Those SAMs were micropatterned by vacuum ultraviolet (VUV) light lithography. The 1-alkene SAMs irradiated for 30 min were measured by X-ray photoelectron spectroscopy (XPS). The sample surface irradiated for 30 min was covered with shorter alkyl chains with carboxyl end groups on SiOx since the O and OH radicals produced by VUV irradiation react with alkyl chains. We measured surface potential images of those micro-patterned SAMs with Kelvin probe force microscopy (KPFM). The surface potentials of HD- and OD-SAMs were +60 and +90mV against irradiated regions. The regions of 1-alkene SAMs show higher surface potential than those of irradiated regions due to the presence of carboxyl end groups. The regions of HD- and OD-SAMs showed positive surface potentials against those of irradiated regions. This irradiated region was confirmed to be a carboxyl-terminated surface with short alkyl chains based on XPS analysis. The carboxyl groups are negatively charged, so the surface potential of the irradiated regions is negative against the HD- and OD-SAM regions.

DOI： 10.1143/jjap.42.2534

Principle in imaging contrast in scanning electron microscopy for binary microstructures composed of organosilane self-assembled monolayers

Saito N., Wu Y., Hayashi K., Sugimura H., Takai O.

Journal of Physical Chemistry B Vol. 107 ( 3 ) page： 664 - 667 2003.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Field-emission electron microscopy (FE-SEM) was applied to observe coplanar microstructures composed of two different types of organosilane self-assembled monolayers (SAMs). These binary microstructures were prepared on silicon substrates covered with native oxide by a lithographic technique. Four types of organosilane precursors, they are n-octadecyltrimethoxysilane (ODS), heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (a type of fluoroalkylsilane, FAS), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS), and 4-(chloromethyl)phenyltrimethoxysilane (CMPhS), were used in this study. Micropatterns composed of the SAMs were clearly imaged by FE-SEM at low acceleration voltages, around 0.6 kV. The brightness order of the SAMs in FE-SEM was ODS > AHAPS > CMPhS > FAS. Through ab initio molecular orbital calculations, the origin of this FE-SEM contrast was ascribed to the electron affinity between the SAMs, which governed the FE-SEM image contrast. It has been successfully demonstrated that FE-SEM could provide us chemical information on organic films with a monomolecular thickness on a solid support.

DOI： 10.1021/jp021362r

Imaging micropatterned organosilane self-assembled monolayers on silicon by means of scanning electron microscopy and Kelvin probe force microscopy

Wu Y., Hayashi K., Saito N., Sugimura H., Takai O.

Surface and Interface Analysis Vol. 35 ( 1 ) page： 94 - 98 2003.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Interface Analysis

Field-emission scanning electron microscopy (FE-SEM) and surface potentiometry based on scanning probe microscopy, i.e. Kelvin probe force microscopy (KFM), have been applied to study microstructures consisting of organosilane self-assembled monolayers (SAMs) terminated with -CH3 or -CF3 groups. Onto cleaned Si substrates covered with a thin oxide layer of 2 nm thick, SAMs were formed by chemical vapour deposition using n-octadecyltrimethoxysilane (CH3(CH2)17Si(OCH3)3, ODS) or fluoroalkylsilane (CF3(CF2)7(CH2)2Si (OCH3)3, FAS) as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures composed of ODS, FAS or both were fabricated. Micropatterns of the SAMs on SiO2/Si substrates were clearly imaged by FE-SEM at an acceleration voltage of the electron beam below 1 kV, but image contrasts became faint with an increase in the acceleration voltage. At a voltage of 5 kV there was almost no detectable contrast. An FE-SEM image of the ODS-FAS microstructure acquired at an acceleration voltage of 0.8 kV clearly demonstrated that the region covered with ODS was brighter and thus, emitted secondary electrons more efficiently than the region covered with FAS. Furthermore, as indicated in a KFM image, the region covered with FAS had a surface potential ∼180 mV lower than that of the region covered with ODS. The origin of these image contrasts between ODS- and FAS-SAMs was the large difference in electronic states between ODS and FAS owing to the electron negativity of fluorine atoms.

DOI： 10.1002/sia.1501

Scanning probe surface modification: Chemical conversion of terminal functional groups on organosilane self-assembled monolayers

Sugimura, H; Saito, N; Hayashi, K; Maeda, N; Takai, O

SCANNING TUNNELING MICROSCOPY/SPECTROSCOPY AND RELATED TECHNIQUES Vol. 696 page： 150 - 157 2003

Alkyl self-assembled monolayer prepared on hydrogen-terminated Si(111) through reduced pressure chemical vapor deposition: Chemical resistivities in HF and NH<inf>4</inf>F solutions

Saito N., Youda S., Hayashi K., Sugimura H., Takai O.

Chemistry Letters ( 12 ) page： 1194 - 1195 2002.12

Regulation of the surface potential of silicon substrates in micrometer scale with organosilane self-assembled monolayers

Hayashi K., Saito N., Sugimura H., Takai O., Nakagiri N.

Langmuir Vol. 18 ( 20 ) page： 7469 - 7472 2002.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

Microstructures composed of two types of organosilane self-assembled monolayers (SAMs) terminated with different functional groups have been constructed on silicon substrates covered with native oxide. Surface potential images of these microstructures were acquired by Kelvin-probe force microscopy (KFM). By chemical vapor deposition (CVD), the SAMs were fabricated from n-octadecyltrimethoxysilane (ODS) [H3C(CH2)17Si(OCH3)3], fluoroalkylsilane (FAS), that is, heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [F3C(CF2)7(CH2)2Si(OCH 3)3], and n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) [H2N(CH2)6NH(CH2)3Si(OCH 3)3]. Through a photolithographic technique, binary microstructures consisting of ODS/FAS and ODS/AHAPS were constructed. A surface potential contrast of the two SAMs in each of the binary microstructures was clearly detected by KFM. The surface potential of the FAS-terminated region was ca. 180 mV lower than that of the ODS-terminated region, while the potential of the AHAPS-terminated region was ca. 50 Mv higher. These results agree with surface potentials of the SAMs predicted from dipole moments of the corresponding precursor organosilane molecules as estimated by ab initio molecular orbital (MO) calculations. Moreover, by applying the surface potential contrasts experimentally acquired by KFM to surface potential contrast occupied area with single molecule curves theoretically derived by MO calculations, packing densities of the SAMs prepared by CVD were confirmed ta be smaller than those of Langmuir-Blodgett monolayers.

DOI： 10.1021/la011707h

The decomposition mechanism of p-chloromethylphenyltrimethoxysiloxane self-assembled monolayers on vacuum ultraviolet irradiation

Saito N., Hayashi K., Sugimura H., Takai O.

Journal of Materials Chemistry Vol. 12 ( 9 ) page： 2684 - 2687 2002.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry

The decomposition mechanism of p-chloromethylphenyltrimethoxysiloxane (CMPS) self-assembled monolayers (SAMs) due to vacuum ultraviolet (VUV) irradiation at a wavelength of 172 nm has been studied based on water repellency, X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM). The CMPS-SAMs were prepared through chemical vapor deposition at 100°C. The water contact angle increased dramatically within the first 30 min, reaching a plateau at this point. The saturated water contact angle was 76°. Next, the CMPS-SAMs were irradiated at under 10 Pa from 0 to 30 min. The CMPS-SAMs irradiated for 15 and 30 min were covered with carboxylated hydrocarbon fragments and silanol groups, respectively. KPFM measurements for micro-patterned SAMs, i.e. CMPS/CO2H and CMPS/SiOH, showed that the surface potential of the carboxylated and silanol regions were -16 and +19 mV vs. CMPS-SAM, respectively. The former negative surface potential difference originated in the electronegativity of the CO2H fragments. These results provide us with a route to prepare an organic template for various fields such as bio-sensors, chemical sensors and electrolytes.

DOI： 10.1039/b203643f

Surface potential contrasts between silicon surfaces covered and uncovered with an organosilane self-assembled monolayer

Hayashi K., Saito N., Sugimura H., Takai O., Nakagiri N.

Ultramicroscopy Vol. 91 ( 1-4 ) page： 151 - 156 2002.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Ultramicroscopy

Surface potentials of Si substrates covered with a organosilane self-assembled monolayers (SAMs) were measured with reference to the substrate uncovered with the SAM using Kelvin probe force microscopy. Based on a photolithographic technique, the reference surface was prepared in a micrometer scale on each of the samples. SAMs were prepared from n-octadecyltrimethoxysilane [ODS: CH3(CH2)17Si(OCH3)3], 3,3,3-trifluoropropyltrimethoxysilane [FAS3: CF3(CH2)2Si(OCH3)3], heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS17: CF3(CF2)7(CH2)2Si (OCH3)3] or n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS: H2N(CH2)6NH(CH2)3Si (OCH3)3) by chemical vapor deposition. Potentials of the surfaces covered with ODS-, FAS3- and FAS17-SAMs became more negative than the uncovered Si substrate, while the surface covered with AHAPS-SAM showed a more positive surface potential than the reference. The potential contrasts of these SAMs to the reference were -25, -170, -225 and +50mV for ODS-, FAS3-, FAS17- and AHAPS-SAMs, respectively. These results almost agreed with potentials expected from the dipole moments of the corresponding precursor molecules estimated by ab initio molecular orbital calculation, except for FAS3-SAM. Despite FAS3 molecule having a larger dipole moment than FAS17 molecule, the surface potential contrast of FAS3-SAM was smaller than that of FAS17-SAM, since surface coverage of FAS3-SAM was relatively incomplete compared with the other SAMs. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-3991(02)00094-3

Surface potential images of self-assembled monolayers patterned by organosilanes: Ab initio molecular orbital calculations

Saito N., Hayashi K., Sugimura H., Takai O., Nakagiri N.

Surface and Interface Analysis Vol. 34 ( 1 ) page： 601 - 605 2002.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Interface Analysis

Self-assembled monolayers (SAMs) with different function terminal groups were prepared on substrates of n-type silicon by chemical vapour deposition (CVD) from n-octadecyltrimethoxysilane (ODS: H3C(CH2)17Si(OCH3)3), heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FAS: F3C(CF2)7 (CH2)2Si(OCH3)3), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS: H2N(CH2)6NH(CH2)3 Si(OCH3)3) and 4-(chloromethyl)phenyltrimethoxysilane [CMPS: H2ClC(C6H4)Si(OCH3)3]. The sample surfaces covered with ODS-SAM were irradiated under a reduced pressure of 10 Pa with vacuum ultraviolet (VUV) light through a photomask. Then, the irradiated areas with the ODS-SAM removed were covered with another SAM by CVD. Surface potential images of the patterned areas were measured by Kelvin probe force microscopy (KPFM) and explained by ab initio molecular orbital (MO) calculations. The KPFM measurements showed that the surface potential contrasts of the FAS-, AHAPS- and CMPS-SAMs against the ODS-SAM were about -170, +50 and -30 mV, respectively. The surface potentials as a function of area occupied by a molecule were predicted using the respective dipole moments perpendicular to substrates, which were obtained by the ab initio MO calculations. The predicted surface potentials of the FAS-, CMPS- and AHAPS-SAMs approximately agreed with the measured values at areas of about 1.5, 1.6 and 0.6 nm2 per molecule. The ab initio MO calculations also showed differences in surface potentials appearing due to the differences in Fermi levels of the respective SAMs.

DOI： 10.1002/sia.1369

Surface potential microscopy for organized molecular systems

Sugimura H., Hayashi K., Saito N., Nakagiri N., Takai O.

Applied Surface Science Vol. 188 ( 3-4 ) page： 403 - 410 2002.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

Surface potentials of organosilane self-assembled monolayers (SAMs) formed on silicon substrates were measured using Kelvin-probe force microscopy (KFM) employing a SAM formed from n-octadecyltrimethoxysilane [ODS: CH 3 (CH 2 ) 17 Si(OCH 3 ) 3 ] as a reference. The reference ODS surface was prepared in a micrometer scale on each of the samples based on a photolithographic technique using vacuum ultra-violet light at 172 nm. Another SAM was prepared on the same sample surface from heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (fluoroalkylsilane with 17 fluorine atoms, FAS17), 3,3,3-trifluoropropyltrimethoxysilane (fluoroalkylsilane with three fluorine atoms, FAS3), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) or (chloromethyl)phenyltrimethoxysilane (CMPS). Potentials of the surfaces covered with FAS17-SAM, FAS3-SAM and CMPS-SAM became more negative than ODS-SAM, while the surface covered with AHAPS-SAM showed a more positive surface potential than the reference. The acquired potential contrasts of the regions covered with FAS17, FAS3, AHAPS and CMPS with reference to ODS were -180, -150, +50 and -30 mV, respectively. These results almost agreed with potentials expected from the dipole moments of the corresponding precursor molecules estimated by ab initio molecular orbital calculation. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(01)00958-8

Carbon Nitrides

Takai O., Lee K., Ohta R., Saito N.

Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering Vol. 68 ( 12 ) page： 1526 - 1529 2002

Surface potentials of patterned organosilane self-assembled monolayers acquired by Kelvin probe force microscopy and ab initio molecular calculation

Saito N., Hayashi K., Sugimura H., Takai O., Nakagiri N.

Chemical Physics Letters Vol. 349 ( 3-4 ) page： 172 - 177 2001.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Physics Letters

This study aimed experimentally and theoretically to reveal the surface potentials of organosilane self-assembled monolayers (SAMs) using Kelvin probe force microscopy (KPFM) and ab initio molecular orbital (MO) calculations, and to distinguish among the surface domains of the SAMs. We prepared the patterned SAMs of n-octadecyltrimethoxysilane [ODS: H3C(CH2)17Si(OCH3)3], heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS: F3C(CF2)7(CH2) 2Si(OCH3)3] and n-(6-aminohexyl)aminopropyltrimethoxysilane [AHAPS: H2N(CH2)6NH(CH2) 3Si(OCH3)3] by chemical vapor deposition (CVD). The surface potentials for FAS-SAM and AHAPS-SAM vs. ODS-SAM in the atmosphere were -170 and +50 mV, respectively. The experimental surface potentials agreed with the calculated ones at the surface area occupied by a molecule of 1.1-1.5nm2molecule-1. © 2001 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(01)01097-1

Kelvin probe force microscopy images of microstructured organosilane self-assembled monolayers

Sugimura H., Hayashi K., Saito N., Takai O., Nakagiri N.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 40 ( 6 B ) page： 4373 - 4377 2001.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

A difference in surface potentials between organosilane self-assembled monolayers (SAMs) was measured by means of Kelvin probe force microscopy (KFM). The SAMs were deposited on a single Si substrate from alkylsilane, that is, octadecyltrimethoxysilane (ODS)[H3C(CH2)17Si(OCH3) 3], and fluoroalkylsilane (FAS), that is, heptadecafluoro-1,1,2,2-tetrahydrodecyl-1-trimethoxysilane [F3C(CF2)7(CH2)2 Si(OCH3)3]. The locations of these SAMs on the substrate were defined by means of a photolithographic technique. The regions terminated with ODS and FAS were clearly distinguished by KFM with the surface potential difference between the ODS- and FAS-terminated surfaces under optimized imaging conditions. The surface potential of the FAS-terminated region was 170 ∼ 180 mV lower than the potential of the ODS-terminated surface. The origin of such a low surface potential of FAS-SAM was ascribed to the larger dipole moment of the FAS molecule induced by the electron negativity of F atoms as estimated from a molecular orbital calculation.

DOI： 10.1143/jjap.40.4373

Surface potential images of microstructured organosilane self-assembled monolayers acquired by Kelvin probe force microscopy

Sugimura, H; Hayashi, K; Saito, N; Takai, O; Nakagiri, N

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 40 ( 2B ) page： L174 - L176 2001.2

Catalytic effects of copper on dibenzo-p-dioxin and polychlorinated dibenzo-p-dioxin generations using ab initio molecular orbital method

Hirota M., Kato J., Saito N., Fuwa A.

Toxicological and Environmental Chemistry Vol. 81 ( 3-4 ) page： 133 - 146 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：Toxicological and Environmental Chemistry

The roles played by copper in dibenzo-p-dioxin formation from the precursor phenol have been investigated using ab initio molecular orbital calculation, and the following catalytic roles of copper has been identified: (i) stabilization of the total energy owing to the absorption of phenol, (ii) reduction of oxygen-hydrogen bond strength in phenol, and (iii) reduction of steric effect of hydrogen atom in pre-dioxin. The catalytic effect of copper has been shown in terms of the smaller apparent activation energy. In the case of polychlorinated dibenzo-p-dioxins generation from precursor polychlorinated phenols, the catalytic roles (i), i.e., the stabilization of the total energy of precursor, would become even stronger. On the other hand, the catalytic roles (ii) and (iii) are unchangeable regardless of the existence of substituted chlorine atom.

DOI： 10.1080/02772240109359026

Behavior of Cu-In-Te electrodeposition from acid solution

Ishizaki T., Saito N., Yata D., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 281 - 284 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Ternary compound-semiconductor, CuInTe2, film was deposited cathodically under potentiostatic conditions on titanium substrate from aqueous solution containing CuCl2, InCl3, TeO2 and HCl in this study. The deposition parameters such as electrolytic solution composition, potential and temperature were optimized for electrodeposition of CuInTe2. Structural characterization of the deposited film was also carried out using XRD and SEM. Electrodeposited films were prepared and analyzed for their chemical composition using ICP. The ICP analyses showed that the stoichiometry of the films could be controlled by (1) the deposition potential and/or by (2) the electrolytic bath composition.

Preparation of YSZ thin films by RF plasma-enhanced metal organic chemical vapor depodition

Nishimura T., Ichikawa T., Saito N., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 267 - 270 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Yttria-stabilized zirconia (YSZ) has high potential to be used as solid-oxide fuel cell (SOFC) electrolyte. However, the high efficiency of SOFC has not been yet achieved due to the high internal resistance of bulk electrolyte. The resistance becomes lower with the decrease in the electrolyte thickness. Thus, the decrease in electrolyte thickness leads to lower internal resistance. The aim of this study is as follows: (a) to prepare the thin films of YSZ by inductively-coupled RF plasma-enhanced metal organic chemical vapor deposition (PEMOCVD) process using Zr(t-OC4H9)4, Y(DPM)3 and oxygen, and (b) to reveal the relationship between the structural characterizations and the process parameters.

The roles of metallic compounds on dioxins generation-decomposition behavior from thermodynamics and quantum chemistry

Saito N., Hirota M., Ishizaki T., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 727 - 732 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Owing to their extremely high toxicity in the environment, the dioxins have been attracting social, technical and scientific attention in recent years. The authors theoretically had predicted the thermodynamics properties of all the dioxins via quantum chemistry and statistical thermodynamics and elucidated the generation-decomposition behavior of dioxins in the equilibrium calculation of C-H-O-Cl system. In actual combustion processes, it is said that metallic compounds have much influence on the dioxins behavior. The aim of this study is to reveal the roles of metallic compounds the generation-decomposition behavior of dioxins is revealed from the viewpoints of quantum chemistry. Especially, the catalytic effect of copper has been investigated for the reaction, 2HCl(g)→H2(g)+Cl2(g) and for the etherification reaction from precursors, which is Phenol(g) here, to dioxins. The catalytic role of Cu is shown to have much influence on the generation -decomposition of dioxins.

Kinetics of SiHCl<inf>3</inf> and SiCl<inf>4</inf> evolution in Si(s)-HCl(g) system simulated by ab-initio MO

Saito N., Ishizaki T., Fuwa A.

Materials Transactions, JIM Vol. 41 ( 3 ) page： 383 - 392 2000.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions, JIM

A reaction model for a HCl(g)-Si(s) system is proposed in this study as follows: first, SiCl2(g) and H2(g) are produced by a heterogeneous surface reaction, and then SiHCl3(g) and SiH2Cl2(g) are produced by the homogeneous reaction between SiCl2(g) and HCl(g) and between SiCl2(g) and H2(g), respectively; finally, SiCl4(g) and SiHCl3(g) are produced by the homogeneous reaction between SiHCl3(g) and HCl(g) and between SiH2Cl2(g) and HCl(g), respectively. The mechanism in the first heterogeneous surface reaction step has been studied extensively in the past. However, the detail of the subsequent homogeneous reactions has not yet been understood. It is important to get information of the chemical kinetics of the reactions derived from the reaction intermediate of SiCl2(g) in the SiCl2(g)-HCl(g)-H2(g) system, so the most plausible elementary reactions of reversible unimolecular fission and chain reaction are proposed here. The structures of the molecules formed in these reactions are optimized using the minimization principle of energy calculated by ab-initio molecular orbital method and also their rate constants are calculated by conventional transition state theory. Using these rate constants, the ordinary differential equations are solved on mass balance, and the time dependent concentration profile of respective chemical species and the prior reaction paths are discussed in this study.

DOI： 10.2320/matertrans1989.41.383

Prediction for thermodynamic function of dioxins for gas phase using semi-empirical molecular orbital method with PM3 Hamiltonian

Saito N., Fuwa A.

Chemosphere Vol. 40 ( 2 ) page： 131 - 145 2000.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemosphere

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzenes and poly-chlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation.

DOI： 10.1016/S0045-6535(99)00215-5

Gas phase equilibria for dibenzo-p-dioxin, dibenzo-p-furan and biphenyl in the C-H-O system

Saito N., Ishizaki T., Fuwa A.

Toxicological and Environmental Chemistry Vol. 74 ( 3-4 ) page： 165 - 177 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：Toxicological and Environmental Chemistry

The gas phase equilibrium calculation for the C-H-O system at atmospheric pressure and temperature from 773 to 1773 K at intervals of 250 K was performed to understand the generation and decomposition behavior of dibenzo-p-dioxin (DD), dibenzo-p-furan (DF) and biphenyl (BP) in relation to the existing oxygen potential. It is possible to categorize these results into three regions from the viewpoint of this potential: region (A), region (B) and region (C) are that of the higher, modest and lower oxygen potential, respectively. In region (A), the equilibrium amounts of DD, DF and BP are nearly zero. In region (B), they increase once and then decrease with rise in temperature. In the most characteristic region (C), they increase uniformly with rise in temperature.

DOI： 10.1080/02772240009358879

Thermodynamic investigation of the effect of oxygen and hydrogen chloride potential upon generation and decomposition behavior of dioxins

Nagahiro Saito, Takahiro Ishizaki, Akio Fuwa

Toxicological and Environmental Chemistry Vol. 75 ( 3-4 ) page： 161 - 179 2000

Language：English Publishing type：Research paper (scientific journal)

The thermodynamic equilibrium of the C-H-O-Cl system has been calculated to elucidate the generation and decomposition behavior of dioxins, and is discussed from the viewpoint of the oxygen and hydrogen chloride potential. The dioxins behavior is greatly dependent on the oxygen potential, i.e. higher temperature and oxygen potential lead to the complete decomposition of dioxins, while low hydrogen chloride potential under insufficient oxygen condition leads to an increase of multi-chlorine displacement of dioxins.

DOI： 10.1080/02772240009358902

Thermodynamic function derivation of dioxin substances using semi-empirical molecular orbital theory

Saito N., Fuwa A.

Proceedings of the TMS Fall Extraction and Processing Conference Vol. 3 page： 2009 - 2018 1999.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the TMS Fall Extraction and Processing Conference

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzens and polychlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation. The values of heats of formation for the dioxin substances and their precursors are calculated in the range of ±200 kJ/mol. The tolerance analysis indicates that the maximum discrepancy with experimental values would be reasonably estimated to be ±28 kJ/mol. The values of standard entropy for these compounds would be in the range of + 270 to + 500 J/mol K, and the estimated discrepancy between the calculated experimental heats of formation would be in the range of + 1 to + 9 J/mol K.

Prediction of Elementary Reaction Mechanism for the CVD Process in Si<inf>2</inf>Cl<inf>6</inf>-H<inf>2</inf> System using Semi-Empirical Molecular Orbital Method

Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 3 ) page： 319 - 325 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

From our previous experimental study of the Si chemical vapor deposition in Si2Cl6-H2 system, the following elementary reaction mechanism was proposed: decomposition of Si2Cl6 to produce SiCl2, which becomes the adsorbent; Si2Cl6(g) → 2SiCl3(g) → SiCl4(g) + SiCl2(g) (→ SiCl2(a)), and hydrogen reduction reaction of the absorbed SiCl2 to produce Si(s). The preliminary quantum chemistry study for this reaction mechanism has shown that the reaction is so infeasible that the above-mentioned elementary reaction mechanism is unreasonable. The most feasible and appropriate reaction mechanism has been shown as follows: (Step 1) Si2Cl6(g) → SiCl4,(g) + SiCl2(g) (Step 2) SiCl2(g) +a → SiCl2(a) (Step 3) SiCl2(a) + H2(g) → SiCl(a) + 2HCl(g) (Step 3-1) SiCl2(a) + H2(g) → Si-2HCl(a) (Step 3-2) Si-2HCl(a) → Si(a) + 2HCl(g) where, a is the active site on silicon surface. On the assumption that step 3 is the rate-determining step, this elementary reaction mechanism can explain the experimental observation in the rate expression on the concentration dependence with respect to Si2Cl6 and H2.

DOI： 10.2320/jinstmet1952.63.3_319

Prediction of pressure dependent rate constant for the reaction, SiH<inf>4</inf>(g)→SiH<inf>3</inf>(g)+H(g), using RRKM theory aided by ab-initio MO

Saito N., Hirota M., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 4 ) page： 520 - 526 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

The pressure dependent rate constant for the reaction, SiH4(g)→SiH3(g)+H was predicted using the Rice-Ramspger-Kassel-Marcus theory aided by Ab-initio molecular orbital (MO). It was calculated under conditions in which the temperatures were from 600 to 1500 K intervals of 100 K. The Arrhenius type rate expression was shown.

DOI： 10.2320/jinstmet1952.63.4_520

Effect of citric acid and EDTA addition on Cu-In alloy electrochemical deposition

Ishizaki T., Saito N., Fuwa A.

Materials Transactions, JIM Vol. 40 ( 9 ) page： 867 - 870 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions, JIM

The standard electrode potential for Cu is 0.34 V and that of In is -0.34 V, which means that their deposition potentials are far apart, making the co-deposition difficult from a simple solution containing Cu and In ions. In order to bring these deposition potentials closer, a complex forming reagent of citric or EDTA is added to the CuSO4-In2(SO4)3 solution. The effect of these reagents was examined by linear sweep voltammetric measurement. An electrochemical deposition experiment of Cu-In alloy was conducted where effect citric acid or EDTA addition, current density and Cu concentration were examined.

DOI： 10.2320/matertrans1989.40.867

Theoretical analysis for thermal chemical vapor deposition from Tetraethoxysilane using a semi-empirical molecular orbital method

Hirota M., Saito N., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 7 ) page： 931 - 937 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

In order to elucidate the reaction mechanism for the Tetraethoxysilane (TEOS) thermal decomposition at atmospheric pressure, its pertinent elemental reactions involving the SiO(OC2H5)2 reaction intermediate were first proposed. For respective species formed in these elemental reactions, the total energy and the electronic state were calculated using a semi-empirical molecular method. The adsorption process which involves adsorbent species formation and surface reaction mechanism were then analyzed from the standpoint of molecular orbital formation and charge transfer mechanism, and the results are summarized as follows: (1) A reaction intermediate, SiO(OC2H5)2(1A1), is probably formed through the following β-elimination reaction route: Si(OC2H5)4(1A1)→SiO(OC2H5) 2(1A1)+C2H4(1A1)+C2H5OH (1A1). (2) The adsorption of SiO(OC2H5)2(1A1) on SiO2 occurs with charge transfer from the dangling bond of silicon atom at an active site of the SiO2 surface to the π*-LUMO unoccupied orbital of SiO(OC2H5)2(1A1). (3) The sequence of surface reactions is considered as follows: (1) First, a dissociation reaction of C2H5(2A′) takes place, whereby producing a double bond between silicon atom and oxygen atom of the intermediate, since they possess unpaired electrons. (2) Si-O bond is successively formed following the mechanism similar to the one operating in the adsorption of SiO(OC2H5)2(1A1) on SiO2. (3) Electronic state of the reactant finally formed is in the 1A1 state, which has a σ-orbital to be fully occupied with electrons.

DOI： 10.2320/jinstmet1952.63.7_931

Texture of thin silicon films deposited from Si<inf>2</inf>Cl<inf>6</inf>

Kato Y., Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 60 ( 8 ) page： 744 - 750 1996.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

Thin Silicon films were deposited on non-crystal quartz glass substrates by hydrogen reduction of Si2Cl6 at temperatures from 650 to 900 °C in a horizontal hot wall reactor. The microstructures of the thin silicon films deposited under various experimental conditions were analyzed. The thin silicon films deposited from 750 to 850 °C have the highest degree of preferred (220) plane orientation with the 〈111〉 direction along the plane, and the cross-sectional morphology exhibits a columnar structure. The experimental values of the lattice spacing approach a value cited in JCPDS for the films deposited in a higher temperature range. In the lower temperature range the morphology of surface is flat and smooth, and in the higher temperature range the surface becomes uneven remarkably.

DOI： 10.2320/jinstmet1952.60.8_744

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