Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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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

Microarc plasma treatment of titanium and aluminum surfaces in electrolytes

Anita V., Saito N., Takai O.

Thin Solid Films Vol. 506-507 page： 364 - 368 2006.5

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

The advanced plasma process of microarc treatment in electrolytes was utilized to prepare oxide layers on aluminum and titanium substrates by anodic conversion. This paper reports results on morphology, structure, growth rates, hardness and water contact angle measurements of titanium and aluminum oxidized surfaces obtained by microarc discharge in ecologically clean and safe electrolytes. Porous oxide layers were formed on the sample surface after the microarc treatment. The morphology of surfaces was dependent on the current intensity during the treatment. The pore diameter in the films decreased with the increase in current intensity and the thickness of the oxide film increased almost linearly with the time of treatment for a constant input power. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.08.083

Visualization of human plasma fibrinogen adsorbed on highly oriented pyrolytic graphite by scanning probe microscopy

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

Surface Science Vol. 600 ( 8 ) page： 1674 - 1678 2006.4

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

Human plasma fibrinogen (HPF) was observed by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) conducted in non-contact mode. The HPF was adsorbed on a highly oriented pyrolytic graphite (HOPG) substrate as single molecules, as aggregated bundles, and as aggregated fibers. Topographic and phase images confirmed structural changes in the HPF after exposure to air, while topographic and KPFM images confirmed fibers with the width of a single HPF molecule. Additionally, KPFM confirmed the surface potential difference between the HPF and the HOPG, and periodical potential drop reflecting the E and D domains in the fiber. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2005.12.058

Carbohydrate Microarrays by Click Chemistry

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

Trans. Mater. Research. Soc. J. Vol. 31 page： 659-703 2006

Micropatterned saccharide display on the silicon surface

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

Polymer Preprints, Japan Vol. 54 ( 1 ) 2005.12

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

The immobilization and the micro-patterning of biomolecules on the solid surfaces are paid much attention for the application of biomaterials, and biosensors. Micro-patterned carbohydrates on solid surfaces are useful to analyze carbohydrate-protein interactions and to fabricate the scaffolds of cell cultivation. We have proposed a new method for micro-patterned carbohydrate display. The micropattern composed of hydrophobic and electrostatically positive regions were fabricated by methyl and amino terminated self-assembled monolayers (SAM). The patterned substrates were incubated in two types of aqueous solutions of PVLA and Heparin, in this order. The PVLA and Heparin site-selectively adsorbed on methyl and amino terminated SAMs, respectively. It indicated that the two dimensional matrix of PVLA and Heparin can be fabricated on the micro-patterned substrate. The micropatterning of two different components on one substrate enables two different biomacromolecules to be self-assembled into micro pattern.

Photolithographic patterning of dendrimer monolayers and pattern-selective adsorption of linear macromolecules

Yamazaki T., Imae T., Sugimura H., Saito N., Hayashi K., Takai O.

Journal of Nanoscience and Nanotechnology Vol. 5 ( 11 ) page： 1792 - 1800 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology

Alkyl groups of n-octadecyltrimethoxysilane (ODS) in a self-assembled monolayer on a silicon substrate were oxidized to carboxyl groups by partial irradiation of vacuum ultra-violet light under the photomask, producing a COOH/ODS line pattern. After active esterification of carboxyl groups, two kinds of amine-terminated dendrimers, poly(propyleneimine) and poly(amido amine) (PAMAM) dendrimers, were immobilized on a COOH line through amide-bond so that photolithographic dendrimer/ODS pattern was finally fabricated. Preparation was certified by atomic force microscopy (AFM) and surface-enhanced infrared absorption spectroscopy at transmission mode. Adsorption of linear macromolecutes was examined on PAMAM dendrimer/ODS pattern. After adsorption of poly-L-glutamic acid (PGA) at a pH below α-helix-random coil transition, rod-shape texture was observed only on the dendrimer line in an AFM image. This texture is an aggregate of α-helical PGA. Sodium hyaluronate and DNA were also adsorbed selectively on the dendrimer line, keeping the line profile, although characteristic textures were not observed. Copyright © 2005 American Scientific Publishers All rights reserved.

DOI： 10.1166/jnn.2005.434

Properties of DLC thin films produced by RF PE-CVD from pyrrole monomer

Takai O., Anita V., Saito N.

Surface and Coatings Technology Vol. 200 ( 1-4 SPEC. ISS. ) page： 1106 - 1109 2005.10

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

This paper reports the properties of diamond like carbon (DLC) thin films obtained in a capacitively coupled, RF powered, plasma enhanced chemical vapor deposition (PE-CVD) system. A precursor used was pyrrole, one of the most known monomers for conductive polypyrrole polymer processing. The deposition rate of thin films was high: 74 nm/min at 50 W and 425 nm/min at 400 W input power. The hardness and elastic modulus of thin films reached the highest values of 16.5 and 148 GPa at 400 W and the surface morphology of the films did not suffer important changes in the interval of utilized input powers: RMS roughness decreased from 0.45 nm at 50 W to 0.20 nm at 400 W. All deposited films were transparent in the infrared range. Raman measurements revealed that the increase of the input power led to a decrease of the sp3 and an increase of sp2 bonded carbon atoms in thin films. The resistivity of DLC thin films was very high for low values of RF input power (ρ> 107 kΩ cm) and decreased at higher values of input power (ρ≈ 55 kΩ cm at 400 W). By using nitrogen as a doping element the resistivity decreased to ρ ≈ 3.5 kΩ cm at 400 W and 20 sccm N2. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2005.02.024

Surface-potential reversibility of an amino-terminated self-assembled monolayer based on nanoprobe chemistry

Saito N., Lee S., Takahiro I., Hieda J., Sugimura H., Takai O.

Journal of Physical Chemistry B Vol. 109 ( 23 ) page： 11602 - 11605 2005.6

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

Nanoprobe chemistry offers a promising approach for the construction of nanostructures consisting of organic molecules by employing the tip of a scanning probe microscope. In a previous report, we demonstrated that a nitroso-terminated surface on an organosilane self-assembled monolayer could be converted into an amino-terminated surface by applying such a nanoprobe electrochemical technique. This paper reports on surface-potential reversibility originating from a reversible chemical reaction between amino and nitroso groups. In addition, we demonstrate surface-potential memory based on this chemical reversibility. Ammo-terminated SAMs were prepared from p-aminophenyl-trimethoxysilane through chemical vapor deposition. Surface potentials were acquired by Kelvin force microscopy. When scanning probe lithography was conducted with a gold tip at positive-bias voltages, the surface potential of the scanned area shifted dramatically in the negative direction. Scanning with negative-bias voltages led to positive shift in the surface potential of the scanned area. The surface potential could be recovered even after multiple scannings with positive and negative applied bias voltages. On the basis of this discovery, we also succeeded in demonstrating surface-potential memory via our nanoprobe electrochemical technique. © 2005 American Chemical Society.

DOI： 10.1021/jp044943k

An investigation into the effect of ionic species on the formation of ZnTe from a citric acid electrolyte

Ishizaki T., Saito N., Takai O., Asakura S., Goto K., Fuwa A.

Electrochimica Acta Vol. 50 ( 16-17 ) page： 3509 - 3516 2005.5

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

Cathodic electrodeposition of ZnTe film was carried out on Au/Cu substrate using three kinds of citric acid electrolytes, each with a different counter anion, i.e., sulfate, chloride, or nitrate ions, to investigate the anion species' influence on the morphology, composition and structure of the resulting electrodeposited ZnTe films. Both chloride and nitrate electrolytes gave crystalline ZnTe films with almost stoichiometric ZnTe composition under electrolytic conditions similar to those optimized previously for sulfate electrolyte. The mean crystallite size of the electrodeposited ZnTe films ranged from 13 to 37 nm. The effect of the ionic species on the crystallite size was also investigated. The degree of ZnTe(1 1 1) plane orientation of the films obtained from nitrate electrolyte was stronger than that of the films from sulfate or chloride electrolytes. High resolution SEM observations revealed different morphologies depending on the anion in the electrolytic solution. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2004.12.028

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