Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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

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