Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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

Local generation of carboxyl groups on an organic monolayer through chemical conversion using scanning probe anodization

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

Materials Science and Engineering C Vol. 27 ( 5-8 SPEC. ISS. ) page： 1241 - 1246 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Science and Engineering C

An organic monolayer directly attached to silicon was prepared through a reaction between 1,7-octadien (OD) and hydrogen-terminated silicon. The OD-monolayer had H2C-terminated groups. The properties of OD-monolayer were evaluated by atomic force microscopy (AFM), ellipsometry and water contact angle measurements. The H2C-terminated groups were site-selectively oxidized through scanning probe anodization and ultraviolet (VUV) irradiation. The sample surfaces fabricated were evaluated by Kelvin force probe microscopy (KPFM) and X-ray photoelectron spectroscopy (XPS). Chemical conversion of functional group in the OD-monolayer was evaluated based on the surface potential change and the immobilization of fluorescence-labeled spheres onto the sample surfaces. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2006.07.002

Fabrication and self-assembly of hydrophobic gold nanorods

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

Journal of Physical Chemistry B Vol. 111 ( 30 ) page： 8891 - 8898 2007.8

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

Hydrophobic gold nanorods were fabricated from hydrophilic gold nanorods coated with hexadecyltrimethylammonium bromide by treating with mercaptopropyltrimethoxysilane (MPS) and subsequently octadecyltrimethoxysilane (ODS). The fabrication of the hydrophobic shell went through the process of (1) binding MPS onto the nanorods, (2) hydrolysis of methoxysilanes, and (3) immobilization of ODS by dehydration condensation. The 2- or 3-D ordered structures of hydrophobic nanorods were self-assembled by the evaporation of solvent on a substrate. The aspects of 2-D assemblies were dependent on the concentration of the nanorods, as was seen in transmission electron microscopic images. At a low concentration, the nanorods assembled parallel to the substrate, whereas they stood on the substrate at a high concentration. On the other hand, in a solid of the gold nanorods, the formation of the 3-D assembly was confirmed by small-angle X-ray scattering. The assembly consisted of hexagonal arrays of the gold nanorods and their lamellar accumulation. © 2007 American Chemical Society.

DOI： 10.1021/jp072524s

Atmospheric plasma-calcination of mesoporous tungsten oxide utilizing plasma dielectric barrier discharge

Baroch P., Hieda J., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 12 ) page： 4905 - 4908 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

The fabrication of mesoporous tungsten oxide films by spin-coating method followed by an atmospheric plasma-calcination method is described and discussed here. For the calcination process the dielectric barrier discharge system generating homogenous atmospheric plasma discharge was designed and used. By this method, large surface area mesoporous films, with disordered pores of average diameter size of about 4 to 5 nm were synthesized. All the plasma-calcined films exhibit amorphous structure. The process of calcination was evaluated by FT-IR spectroscopy and in comparison with other methods a very high speed of calcination process was achieved. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.10.088

Submicron optical near-field diffraction patterns obtained by irradiation of octadecyltrimethoxysilane self-assembled monolayers with light at 157 nm

Nae F., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 12 ) page： 5147 - 5152 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

Nanostructures less than 200 nm in size are created by the Fresnel diffraction of 157 nm light at the aperture margins of a photomask through proximity irradiation of an octadecyltrimethoxysilane self-assembled monolayer. Photochemical decomposition of the organic monolayer creates complex nanostructure patterns, according to the light intensity distribution at the substrate location. Dimensions and distribution of the nanostructures correlate well with the spatial distribution of the light intensity calculated using the Fresnel equations. © 2006.

DOI： 10.1016/j.tsf.2006.10.090

Patterned hydrophobic-hydrophilic templates made from microwave-plasma enhanced chemical vapor deposited thin films

Wu Y., Kouno M., Saito N., Andrei Nae F., Inoue Y., Takai O.

Thin Solid Films Vol. 515 ( 9 ) page： 4203 - 4208 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

In the present research, nano-structured materials exhibiting super-hydrophobic behavior obtained by microwave-plasma enhanced chemical vapor deposition (MPECVD) had their surface chemical status altered through vacuum ultraviolet (VUV) light irradiation. Falling water droplets rolled and bounced without wetting or spreading over the initially super-hydrophobic surfaces. We demonstrate a surface preparation technique to create a patterned super-hydrophobic/super-hydrophilic substrate in which micropatterns with super-hydrophobic and super-hydrophilic regions were prepared through irradiation with VUV light. To confirm the method, growth of water droplets is observed in situ on such super-hydrophobic/super-hydrophilic micropatterns. We discuss the applicability of the super-hydrophobic/super-hydrophilic pattern to the bottom-up assembling of materials, like site-selective electroless Cu plating on patterned substrates made of paper and selective cell culture experiments. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.02.065

The importance of precursor molecules symmetry in the formation of self-assembled monolayers

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

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 46 ( 3 A ) page： 1118 - 1123 2007.3

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

We investigated the role of precursors molecular symmetry in the self-assembled formation of organosilane monolayer by applying atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD), Fourier transform infrared spectroscopy (FT-IR) and contact angle measurement. Octadencyltrichlorosilane (OTS), octadecylmethydichlorosilane (ODCS), and octadecyldimethylchlorosilane (ODMS) were used as raw materials to form organosilane monolayers. The organosilane monolayers were prepared by a liquid phase method at a reaction temperature of 5°C and an humidity in reactor of 50%. AFM observations suggested that only OTS molecules grew two-dimensionally on the Si substrate surface. In GIXD results showed these OTS molecules to be arranged in a crystalline state on the Si surface. Thus "self- organization" occurred during OTS monolayer formation process. However, in the case of ODCS and ODMS, the monolayers formed were in an amorphous state. In addition, FT-IR and water contact angle measurement indicated that the packing density of the OTS monolayer was higher than that of the ODCS and ODMS monolayers. Only when the precursor molecules had an axis where the silanol groups were in three-fold did "self-organization" occurs in the formation of the organosiloxane monolayer. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.1118

A micropatterned multifunctional carbohydrate display by an orthogonal self-assembling strategy

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

Biomacromolecules Vol. 8 ( 2 ) page： 753 - 756 2007.2

Fabrication and characterization of ultra-water-repellent alumina-silica composite films

Ishizaki T., Saito N., Inoue Y., Bekke M., Takai O.

Journal of Physics D: Applied Physics Vol. 40 ( 1 ) page： 192 - 197 2007.1

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

Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150°, whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica-alumina system. © 2007 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/40/1/014

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