Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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 Open Access

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 Open Access

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

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