Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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 Open Access

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

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