Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Influence of Ar gas flow rate in organosilicon plasma for the fabrication of SiO:CH thin films by PECVD method

Yun Y., Yoshida T., Shimazu N., Nanba N., Inoue Y., Saito N., Takai O.

Surface and Coatings Technology Vol. 202 ( 22-23 ) page： 5259 - 5261 2008.8

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

SiO:CH films were prepared by capacitively coupled RF PECVD to investigate the dependence on Ar gas flow ratio based on plasma reactions and film properties. The introduced Ar gas flow rate increases an the amorphous carbon network, and dangling bonds or -OH terminations due to Ar ion bombardment. Moreover, Ar gas flow rate alters the dissociation reactions and leads to change the chemical bonding states and the water contact angle. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2008.06.004

Size-regulated gold nanoparticles fabricated by a discharge in reverse micelle solutions

Hieda J., Saito N., Takai O.

Surface and Coatings Technology Vol. 202 ( 22-23 ) page： 5343 - 5346 2008.8

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

A discharge was applied to reverse micelle solutions, which provided constant volume nanoreactors, to synthesize size-regulated gold nanoparticles. The molar ratio of water to surfactant, W, was varied to regulate the nanoparticle size. A pulsed power supply was used to generate the discharge in the reverse micelle solutions. The applied voltage, pulse width, and frequency were 960 V, 2 μs, and 15 kHz, respectively. The synthesized gold nanoparticles were observed by transmission electron microscopy (TEM). Surface plasmon absorption band of the gold nanoparticles was measured by ultraviolet-visible (UV-Vis) spectroscopy. TEM images showed that the average particle size varied from 3.8 to 11 nm in diameter as W was increased. Thus, the size of gold nanoparticles can be regulated by the volume of water droplets in the reverse micelle solutions. Reduction of [AuCl4]- ions and formation of gold nanoparticles proceeded only inside the water droplets formed by reverse micelles. These nanoreactors regulated by reverse micelles lead to the uniform growth of gold nanoparticles. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2008.06.092

Effect of reaction temperature on growth of organosilane self-assembled monolayers

Lee S., Ishizaki T., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 47 ( 8 PART 1 ) page： 6442 - 6447 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The effect of reaction temperature on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) self-assembled monolayers (SAM) was investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD) measurement, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). OTS SAM was prepared by a liquid phase method and chemical vapor deposition. In the liquid phase method, OTS SAM was prepared in the temperature range from 5 to 40 °C. In the reaction temperature range from 5 to 30 °C, OTS molecules formed domain structures early in the growth process and grew two-dimensionally on SiO2 substrates. In addition, the crystalline peaks of GIXD measurements indicated that OTS SAM prepared at lower temperatures (5-30 °C) grew in the crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS SAM prepared at 40 °C showed an amorphous structure. XPS and FT-IR spectra showed that the SiO2 peak increased while reaction temperature decreased. These results indicated that the formation of a siloxane bond between OTS molecules was important for the self-organization of the OTS monolayer. In addition, FT-IR measurement indicated that the packing density of the OTS monolayer prepared at lower temperatures was higher than that prepared at higher temperatures by chemical vapor deposition. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.6442

Effects of humidity and solution age on growth of organosilane self-assembled monolayers

Lee S., Ishizaki T., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 47 ( 8 PART 1 ) page： 6416 - 6421 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The effect of humidity on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) monolayers was investigated using an atomic force microscope (AFM), grazing incidence X-ray diffraction (GIXD), and Fourier transform IR spectroscopy (FT-IR). OTS self-assembled monolayers (SAMs) were prepared under humidity ranging from 5 to 80%. Under humidity ranging from 15 to 80%, OTS molecules produced domain structures early in the growth process that grew twodimensionally on SiO2 substrates. Also, the crystalline peaks of the obtained from the GIXD measurement indicated that OTSSAMs prepared under high humidity (15-80%) had grown in a crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS-SAMs prepared under 5% humidity were in an amorphous structure. OTS-SAMs prepared at high humidity were denser than those prepared at low humidity. The domain size early in the growth process increased in proportion to the solution age. This shows that the reaction rate is governed by the hydrolysis of organosilane. On the other hand, solution age has no great influence on the density of the OTS-SAMs under conditions of more than 50% humidity. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.6416

Bipolar pulsed electrical discharges in liquid

Baroch P., Saito N.

IEEE Transactions on Plasma Science Vol. 36 ( 4 PART 1 ) page： 1156 - 1157 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Plasma Science

Electrical discharges in water offer a unique plasma source which can be utilized in various novel applications. These discharges are distinguished for the rapid in situ production of highly reactive species when high voltage of about 10-20 kV is applied. Images of the plasma discharges in the water, which are generated by using high-frequency bipolar pulse power supply at relatively low ignition voltages, are presented here. © 2008 IEEE.

DOI： 10.1109/TPS.2008.924488

Morphology of high-frequency electrohydraulic discharge for liquid-solution plasmas

Takeda T., Chang J.S., Ishizaki T., Saito N., Takai O.

IEEE Transactions on Plasma Science Vol. 36 ( 4 PART 1 ) page： 1158 - 1159 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Plasma Science

An experimental investigation has been conducted to study the morphology of high-frequency electrohydraulic discharge for a liquid-solution plasma, where the liquid-solution plasma is currently investigated for the fabrication of nanometer-size metal particles and inactivation of bacteria. The fundamental nature and basic characteristics of this new type of plasma is relatively not well investigated. In this paper, this type of liquid-solution plasma was experimentally investigated along with discharge morphology. © 2008 IEEE.

DOI： 10.1109/TPS.2008.925713

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Hieda J., Saito N., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 26 ( 4 ) page： 854 - 856 2008.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2 O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2 O2 and electron donation of H radicals to the solution. After the pH stopped decreasing, H radicals mainly reacted as a reducing agent. The decrease in pH allowed redissolution of the gold nanoparticles. The gold dust particles that were not completely dissolved acted as new seeds for nucleation. Thus, the two reaction steps, nucleation and nuclear growth, occur during the formation of gold nanoparticles with exotic shapes. © 2008 American Vacuum Society.

DOI： 10.1116/1.2919139

Bipolar pulsed electrical discharge for decomposition of organic compounds in water

Baroch P., Anita V., Saito N., Takai O.

Journal of Electrostatics Vol. 66 ( 5-6 ) page： 294 - 299 2008.5

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

This work focuses on the development of an underwater plasma source that may open new possibilities in wastewater treatment processes by enabling the operation of the discharge under relatively low discharge voltages (sub-kV region). For this purpose, two systems, based on a wire-to-wire electrode configuration: (i) with and (ii) without gas bubbling, were designed. Both systems were operated utilizing a high-frequency bipolar DC pulse power supply. Properties of generated plasma were investigated by electrical and optical emission spectroscopy methods. Subsequently, determination of generation of active species and preliminary tests on the decomposition of organic dye in aqueous solution were carried out. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elstat.2008.01.010

Special type of plasma dielectric barrier discharge reactor for direct ozonization of water and degradation of organic pollution

Baroch P., Saito N., Takai O.

Journal of Physics D: Applied Physics Vol. 41 ( 8 ) 2008.4

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

A system based on the dielectric barrier discharge (DBD) with improved discharge homogeneity, used for direct ozonization and purification of water, is presented here. A special design of the atmospheric DBD system is characterized by incorporation of a porous ceramic segment in the zone between electrodes. This porous segment was placed on the metallic electrode and served as a guide for flowing water. Due to the hydrophilic force it allowed the water to remain undisturbed by the electrical discharge. This feature enabled a reduction of the discharge gap and subsequently an increase in the intensity, stability and homogeneity of the discharge. It was observed that under such a configuration a transition from the filamentary mode to the semi-homogeneous mode of the plasma discharge could be realized. Discharge properties were investigated by the optical emission spectroscopy method and the results showed the domination of nitrogen lines in the UV-A region. Further it was observed that the system can be operated in a wide range of liquid conductivities and under negligible heat deposition to the liquid solution. Finally, the formation of dissolved ozone and hydrogen peroxide in the deionized water was measured and decomposition tests with organic dye were performed. © 2008 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/41/8/085207

Attenuated total reflectance spectroscopy of simultaneous processes: Corrosion inhibition of cuprous oxide by benzotriazole

Bratescu M.A., Allred D.B., Saito N., Sarikaya M., Takai O.

Applied Surface Science Vol. 254 ( 10 ) page： 2960 - 2966 2008.3

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

Attenuated total reflectance (ATR) spectroscopy was used to perform in situ studies of the corrosion inhibition of cuprous oxide (Cu 2 O) by benzotriazole (BTA) in aqueous solution at concentrations from 1 to 20 μM. Because two separate processes occur simultaneously, that of Cu 2 O corrosion and corrosion inhibition by BTA adsorption, the spectral information was subjected to deconvolution by a conjugate gradient minimization algorithm. Under these conditions, a solution phase concentration of 7-10 μM BTA nearly completely inhibited the corrosion of Cu 2 O in deionized water. Using a Langmuir adsorption model, this represented only 25% of the maximally covered surface area. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2007.10.048

Scanning probe microscopy for the analysis of composite Ti/hydrocarbon plasma polymer thin films

Choukourov A., Grinevich A., Slavinska D., Biederman H., Saito N., Takai O.

Surface Science Vol. 602 ( 5 ) page： 1011 - 1019 2008.3

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

Composite Ti/hydrocarbon plasma polymer films with different Ti concentration were deposited on silicon by dc magnetron sputtering of titanium in an atmosphere of argon and hexane. As measured by Kelvin force microscopy and visco-elastic atomic force microscopy, respectively, surface potential and hardness increase with increasing Ti content. Adhesion force to silicon and to fibrinogen molecules was stronger for the Ti-rich films as evaluated from the AFM force-distance curves. Fibrinogen forms a very soft layer on these composites with part of the protein molecules embedded in the outermost region of the plasma polymer. An increase of the surface charge due to fibrinogen adsorption has been observed and attributed to positively charged αC domains of fibrinogen molecule. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.12.035

Comparative study of the molecular aggregation state of alkyl organic monolayers prepared on Si and hydrogen-terminated Si substrates

Ishizaki T., Saito N., Lee S., Takai O.

Nanotechnology Vol. 19 ( 5 ) 2008.2

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

A comparative study of the molecular aggregation states of n-octadecyltrichlorosilane (OTS) and octadecene monolayers was carried out based on water contact angle, x-ray reflectivity (XR), grazing incidence x-ray diffraction (GIXD), and Fourier transform infrared spectroscopy (FT-IR) measurements. Water contact angle, XR, and FT-IR measurements revealed that the packing density and orientational order of the OTS were higher than those of octadecene. The OTS monolayer was in a hexagonal crystalline state with (10) spacing of 0.417 nm, whereas the octadecene monolayer was in an amorphous state. The growth mechanisms of the OTS and octadecene monolayers are also proposed. The alkyl molecular aggregation states strongly depended on the chemical bonding state at the interface between the alkyl organic molecule and the substrate surface. © IOP Publishing Ltd.

DOI： 10.1088/0957-4484/19/05/055601

'Fabrication and structure of alginate gel incorporating gold nanorods

Mitamura K., Imae T., Saito N., Takai O.

Journal of Physical Chemistry C Vol. 112 ( 2 ) page： 416 - 422 2008.1

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

The gelation of sodium alginate incorporating gold nanorods was investigated. The hybrid gel was obtained by mixing calcium ions with a gel precursor (alginate + nanorod). The gel displayed two plasmon bands in the visible and near-infrared region. The shapes of the hybrid gel grains were controllable, like sphere, ring, and rod. Furthermore, the release of the gold nanorods from the gel phase was observed in a saline solution, accompanying the gel collapse to alginate fibers. Moreover, in the structural investigation of the hybrid gel using small-angle X-ray scattering, it was confirmed that alginate fibers were tightly condensed on the nanorod and formed a shell on it. Such condensation or shell formation resulted from the electrostatic interaction of alginate with hexadecyltrimethylammonium bromide, which protects the nanorods. The hybrid gel retained the same amount of water as the neat gel, although the water content (30 wt %) in a shell on a nanorod was far less than that (98 wt %) of bulk gel. © 2008 American Chemical Society.

DOI： 10.1021/jp076755a

Radio frequency power dependence in formation of SiO:CH thin films by plasma-enhanced chemical vapor deposition

Yun Y., Yoshida T., Shimazu N., Nanba N., Inoue Y., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 46 ( 11 ) page： 7460 - 7464 2007.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

SiO:CH films were prepared by capacitively coupled radio frequency (RF) plasma-enhanced chemical vapor deposition to investigate the dependence on RF power on the basis of plasma reactions and film properties. The RF power dependence can be divided into two broad categories, the reaction-controlled regime (regime R) and the flow rate-controlled regime (regime F). In the regime R, the introduced RF power initially dissociates and recombines the trimethylmethoxysilane reactant, and leads to drastic increase in deposition rate. In the regime F, the insufficient flow of reactants saturates the deposition rate. Moreover, the extra energy dissociates and recombines the reactant drastically and heats electrons in the plasma. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.7460

Application of Ultra-Water-Repellent Surface to Cell Culture

Ino K., Ito A., Wu Y., Saito N., Hibino E., Takai O., Honda H.

Journal of Bioscience and Bioengineering Vol. 104 ( 5 ) page： 420 - 423 2007.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Bioscience and Bioengineering

In this study, we applied an ultra-water-repellent film to cell culture. We cultured cells in droplets on the film and fabricated cell aggregates. Furthermore, we allocated cells on micropatterned surfaces consisting of ultra-water-repellent regions and cell culture-treated regions. The results show that the material is useful for cell culture. © 2007 The Society for Biotechnology, Japan.

DOI： 10.1263/jbb.104.420

A micropatterned carbohydrate display for tissue engineering by self-assembly of heparin

Sato H., Miura Y., Saito N., Kobayashi K., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3871 - 3875 2007.9

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

A novel strategy to construct a fibroblast scaffold on substrates has been demonstrated via top-down photolithography and the subsequent bottom-up processes of molecular self-assembly and molecular recognition. 3-Aminopropyltrimethoxysilane (APS) self-assembled monolayer was micropatterned by photolithography. An anionic polysaccharide heparin was adsorbed selectively on the cationic APS region of the micropatterned substrate. Basic fibroblast growth factor (bFGF) was selectively bound to the displayed heparin region and then micropatterned cultivation of fibroblast cells was successful on the bFGF-heparin-APS substrate. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.066

Electrochemical soft lithography of an 1,7-octadiene monolayer covalently linked to hydrogen-terminated silicon using scanning probe microscopy

Lee S.H., Ishizaki T., Saito N., Takai O.

Surface Science Vol. 601 ( 18 ) page： 4206 - 4211 2007.9

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

Electrochemical scanning probe lithography (SPL) was carried out on a 1,7-octadiene (OD) monolayer directly attached to silicon. The chemical conversion of the OD-monolayer was investigated by Kelvin probe force microscopy (KPFM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and by an adsorption test of amino-modified fluorescent spheres. AFM and KPFM results indicated that the electrochemical reactions induced by SPL were governed by the bias voltage applied between the tip of the scanning probe microscope (SPM) and the substrate. XPS spectra indicated that the vinyl groups on the OD monolayer were oxidized and chemically converted into carboxyl groups at bias voltages of 1-2 V. At bias voltages of more than 3 V, OD molecules on the sample surface were decomposed and silicon oxide was formed on the surface. In addition, the formation of COOH groups was confirmed by the site-selective adsorption of amino-modified fluorescent spheres. However, XPS spectra for sample surfaces scanned at negative bias voltages showed no change since the peak was generally weak. However, KFM and AFM results indicated that at bias voltages of more than -1.5 V, cyclobutane rings formed. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.094

Localized surface plasmon resonance of silicon compounds adsorbed on silver nanoparticles

Bratescu M., Saito N., Mori H., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3886 - 3891 2007.9

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

A simple method to produce silver nanoparticles on a glass surface from silver nanolayer deposited by magnetron sputtering and thermal annealed is presented. Localized surface plasmon resonance of nanoparticles shows a red shift depending on the silver nanolayer thickness, the refractive index and the thickness of an ultra-thin silicon compound adsorbed on the surface. A highly enhanced Raman spectrum of the characteristic groups of a silicon compound adsorbed on the nanoparticles surface was obtained. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.074

SPM analysis of fibrinogen adsorption on solid surfaces

Choukourov A., Grinevich A., Saito N., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3948 - 3951 2007.9

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

The adsorption kinetics, adhesion and orientation of human fibrinogen on solid surfaces have been studied by surface probe microscopy (SPM) and quartz crystal microbalance techniques (QCM). CF3-, NH2-terminated organo-silane self-assembled monolayers (SAM) and OH-terminated silicon dioxide have been used as model surfaces. Furthermore, the interaction of fibrinogen with nanocomposite Ti/hydrocarbon plasma polymer films (Ti/ppCH) deposited by dc magnetron sputtering has also been studied. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.155

Probing into adsorption behavior of human plasma fibrinogen on self-assembled monolayers with different chemical properties by scanning probe microscopy

Ishizaki T., Saito N., Sato Y., Takai O.

Surface Science Vol. 601 ( 18 ) page： 3861 - 3865 2007.9

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

The adsorption behaviors of fibrinogen on the self-assembled monolayers (SAMs) with different chemical properties were investigated using an atomic force microscopy (AFM). AFM images indicated that the adsorption amounts of fibrinogen molecules increased with an increase of the surface hydrophobicity. High-resolution AFM imaging revealed that the fibrinogen conformations adsorbed on the SAM surface changed with dependent on the surface chemistry. The adsorption models of fibrinogen molecules adsorbed on SAM surfaces with different chemical properties were proposed based on the high-resolution AFM images. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.096

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