Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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 Open Access

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

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