Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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

Behavior of various organosilicon molecules in PECVD processes for hydrocarbon-doped silicon oxide films

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

Solid State Phenomena Vol. 124-126 ( PART 1 ) page： 347 - 350 2007

Language：English Publishing type：Research paper (scientific journal) Publisher：Solid State Phenomena

Plasma diagnosis was performed by means of optical emission spectroscopy in the plasma-enhanced chemical vapor deposition process for preparation of hydrocarbon-doped silicon oxide films. The chemical bonding states were characterized by a fourier-transform infrared spectrometer. Based on the results of the diagnosis in organosilane plasma and the chemical bonding states, a reaction model for the formation process of hydrocarbon-doped silicon oxide films was discussed. From the results of optical emission spectroscopy, we found that the oxygen atoms of methoxy groups in TMMOS molecules can be dissociated easily in the plasma and behave as a kind of oxidizing agent. Siloxane bondings in HMDSO, on the other hand, hardly expel oxygen atoms.

DOI： 10.4028/3-908451-31-0.347

Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis

Bratescu M., Suda Y., Sakai Y., Saito N., Takai O.

Thin Solid Films Vol. 515 ( 4 ) page： 1314 - 1319 2006.12

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

The role of carbon atoms in a dc plasma-enhanced chemical vapor deposition for carbon nanotubes (CNTs) synthesis was investigated. It was observed that at 1.33 kPa pressure of CH4 gas in plasma, a high value of the ratio between the intensities of the graphite peak (G peak) and the disorder peak (D peak) in the Raman spectrum corresponds to the maximum value of the excited C number density in the vicinity of the Si substrate. It was found that a CH4 gas pressure higher than 1.33 kPa leads to an increase of the relative density of the C2, C3 molecules and the clusters, and to a decrease of the C excited atom number density in plasma. The presence of a high amount of sp2-graphite in the composition of CNTs observed in Raman spectrum was also confirmed by the measurement of the IR-active G peak at 1584 cm- 1 in the transmission spectrum. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2006.03.022

Degradation of bacteria using pulse plasma discharge in liquid medium

Baroch P., Takeda T., Oda M., Saito N., Takai O.

Conference Record of the International Power Modulator Symposium and High Voltage Workshop page： 482 - 485 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the International Power Modulator Symposium and High Voltage Workshop

The paper reports on the study of an underwater electrical pulse plasma discharge operating under relatively low discharge voltages (below 1 kV) and its utilization for degradation of bacteria contained in the liquid medium. For this purpose, a system based on wire-to-wire electrode configuration was designed. Results show the ability of the system to generate active species, observed by optical emission spectroscopy and also revealed from the change in pH of treated solution. Effective generation of these species then results in a relatively fast decomposition rate of tested organic dyes. Consequent treatment process with two types of bacteria alsoexhibits positive results showing successful and very fast decrease in bacteria population. ©2006 IEEE.

DOI： 10.1109/MODSYM.2006.365289

Multifunctional micropatterning of glycoconjugate polymer via a orthogonal self-assembly

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

Polymer Preprints, Japan Vol. 55 ( 2 ) page： 5260 - 5261 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

We propose a novel strategy for a multiple micropatterned display of carbohydrates by orthogonal supramolecular formation. Two kinds of glycopolymer was self-assembled on the substrate by hydrophobic and electrostatic interaction. Two types of protein and cell was adsorbed on the glycopolymer due to the molecular recognition.

Rapid mass production of gold nanoaprticle from gold salts

Yonezawa T., Oda M., Ishizaki T., Saito N., Takai O.

Polymer Preprints, Japan Vol. 55 ( 2 ) page： 3843 - 3844 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

A novel rapid mass production process of gold nanoparticles by using spark discharge in solution is proposed in this study. Into AuCl4- aqueous solution, gelatin was introduced as the stabilizing reagent. Then, spark discharge at ca. 800 V was applied. The yellow solution turned into dark-red, which suggests the formation of gold nanoparticles protected by gelatin. UV-Vis spectra of the obtained dispersions indicates the complete reduction of Au3+ ions and production of gold nanoparticles. The TEM images revealed that gold nanoparticles were dispersed independently without aggregation. This process is quite unique and easy for mass production of various kinds of metal nanoparticles.

Study of alkyl organic monolayers with different molecular chain lengths directly attached to silicon

Ishizaki T., Saito N., SunHyung L., Ishida K., Takai O.

Langmuir Vol. 22 ( 24 ) page： 9962 - 9966 2006.11

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

Alkyl organic monolayers with different alkyl molecular chain lengths directly attached to silicon were prepared at 160°C from 1-decene (C10), 1-dodecene (C12), 1-tetradecene (C14), 1-hexadecene (C16), and 1-octadecene (C18). These monolayers were characterized on the basis of water contact angle measurement, ellipsometry, X-ray reflectivity (XR), X-ray photoelectron spectroscopy (XPS), and grazing incidence X-ray diffraction (GIXD) to elucidate the effect of the molecular chain length on the molecular arrangement and packing density of the monolayers. Water contact angle and XPS measurements showed that C12, C14, and C16 monolayers have a comparably higher quality, while the quality of C10 and C18 monolayers is worse. GIXD revealed that the alkyl monolayers directly attached to the Si were all amorphously structured regardless of their alkyl chain length. The amorphous structure of the alkyl monolayers could be attributed to the rigid Si-C bonding, low quality of hydrogen-terminated silicon substrate, and/or low mobility of physisorbed molecules. © 2006 American Chemical Society.

DOI： 10.1021/la052342u

Treatment of immobilized collagen on poly(tetrafluoroethylene) nanoporous membrane with plasma

Bratescu M.A., Saito N., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 45 ( 10 B ) page： 8352 - 8357 2006.10

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

In this work we treated type I collagen immobilized on different nanoporous membranes with microwave (MW) argon plasma. Hydrophobic and hydrophilic nanoporous substrates of poly(tetrafluoroethylene), with thickness varying from 35 to 70 μm and a 100nm pore size, were employed as support for collagen immobilization. On the hydrophilic nanoporous membrane, after the MW plasma treatment, the immobilized collagen changed its morphology and showed a tendency to self-assemble in quasi-regular forms as microellipsoids. The presence of collagen immobilized on the nanoporous membrane after the MW plasma treatment was analyzed by detecting in the Raman spectrum an α-helix form, NH deformation vibration, amide II band at .1550 cm-1, a characteristic group frequency of the collagen macromolecule. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.8352

Water droplets interaction with super-hydrophobic surfaces

Wu Y., Saito N., Nae F.A., Inoue Y., Takai O.

Surface Science Vol. 600 ( 18 ) page： 3710 - 3714 2006.9

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

Static and dynamic behavior of water droplets on various super-hydrophobic (SH) surfaces were investigated. First, SH plant leaves were used as samples and we found out that surface nanostructure has a great influence on the droplets dynamic behavior. Then, we made biomimetic structures by depositing SH films through microwave-plasma enhanced chemical vapor deposition (MPECVD). Next, SH surfaces were fabricated by covering previously roughened SiOx films with self-assembled monolayers (SAMs). The substrates were then charged with static electricity, and water droplets falling on tilted charged surfaces leaped up or run uphill at high speeds, proving that not only the surface nanostructure but also its chemical endgroups have a great effect on the water droplets motion on SH surfaces. © 2006.

DOI： 10.1016/j.susc.2006.01.073

Depth profiles of the Fermi level at an amorphous-carbon nitride/SiO<inf>2</inf>/n-type-Si heterojunction interface obtained by Kelvin probe force microscopy

Ishizaki T., Saito N., Ohta R., Takai O.

Diamond and Related Materials Vol. 15 ( 9 ) page： 1378 - 1382 2006.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Diamond and Related Materials

To explore the work function of a typical amorphous-CN film containing a nitrogen concentration of 23.5 at.%, surface potential images were acquired using Kelvin probe force microscopy. Based on the Fermi level of the n-type Si and the contact potential difference between the amorphous-CN film and the n-Si substrate, the work function of the amorphous-CN film was estimated to be 5.2 ± 0.2 eV below its vacuum level. Using the surface potential depth profile for an etched amorphous-CN film, energy diagrams of the amorphous-CN/SiO2/n-Si interface were constructed based on the positional relationship of the Fermi level. These band diagrams showed that band bending occurred at the amorphous-CN/SiO2/n-Si interface despite the Fermi level pinning effect of surface trapping due to the SiO2 insulator layer. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2005.10.001

Synthesis of DLC films by PECVD combined with hollow cathode sputtering

Anita V., Butsuda T., Saito N., Takai O.

Vacuum Vol. 80 ( 7 SPEC. ISS. ) page： 736 - 739 2006.5

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

The mechanical and electrical properties of aluminium-doped diamond-like carbon (DLC) thin films obtained with a hybrid method combining hollow magnetron discharge sputtering and plasma-enhanced chemical vapour deposition (PECVD) are reported. The ratio between the mass flows of methane reactive gas and argon inert gas was found to have a big influence on the properties of doped DLC films. For low mass flow of methane gas the cathode surface was kept in a metallic state. By increasing methane mass flow the cathode surface became to be covered with DLC and the behaviour of the discharge changed, influencing the properties of deposited films. The lowest resistivity (10-4 Ω cm) of thin films was obtained in the metallic state of the cathode but without DLC character, as indicated by Raman measurements. The resistivity increased in the intermediate mode (0.01 Ω cm) and attained higher value (1 Ω cm) in the poisoned state of the cathode. These films presented DLC character, with D and G bands, as revealed by Raman measurements. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2005.11.020

Synthesis of nitrogen-rich carbon nitride thin films via magnetic field-assisted inductively coupled plasma sputtering

Ohta R., Yokota T., Anita V., Saito N., Takai O.

Vacuum Vol. 80 ( 7 SPEC. ISS. ) page： 752 - 755 2006.5

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

Carbon nitride (CNx) thin films were synthesized by magnetic field-assisted inductively coupled plasma (ICP) sputtering. The electron density, electron temperature and optical emission intensity of the plasma state were significantly changed by varying the external magnetic field applied. The CNx thin film with the highest nitrogen content (N/C=1.16) was obtained when the electron density was at its highest and the electron temperature at its lowest. Additionally, the optical emission from atomic nitrogen was the strongest under the same condition. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2005.11.042

Magnetron plasma-enhanced chemical vapor deposition of diamond-like carbon thin films

Anita V., Saito N., Takai O.

Thin Solid Films Vol. 506-507 page： 63 - 67 2006.5

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

An RF magnetron plasma-enhanced chemical vapor deposition system with variable magnetic field (MagPECVD) was utilized for high rate deposition of diamond-like carbon thin films. Deposition rate was nonuniform, with minimum value of 30 nm/min in the center of the cathode where the low ionic flux is determined by the absence of the E × B electronic drift. The highest value of 1029 nm/min was registered in the position of the cathode with the highest ion flux determined by the presence of the E × B electronic drift. Hardness, elastic modulus and RMS roughness of thin films were dependent on local values of magnetic field intensities and the values of input power. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.08.074

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