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Shimoyama, Iwao; Baba, Yuji; Hirao, Norie*
Applied Surface Science, 405, p.255 - 266, 2017/05
Times Cited Count：1 Percentile：5.94(Chemistry, Physical)NEXAFS spectroscopy is applied to study orientation structures of polydimethylsilane (PDMS) films deposited on heteroatom-doped graphite substrates prepared by ion beam doping. The Si 
-edge NEXAFS spectra of PDMS show opposite trends of polarization dependence for non irradiated and N
-irradiated substrates, and show no polarization dependence for an Ar-irradiated substrate. Based on a theoretical interpretation of the NEXAFS spectra via first-principles calculations, we clarify that PDMS films have lying, standing, and random orientations on the non irradiated, N-irradiated, and Ar-irradiated substrates, respectively. Furthermore, photoemission electron microscopy indicates that the orientation of a PDMS film can be controlled with microstructures on the order of 
m by separating irradiated and non irradiated areas on the graphite surface. These results suggest that surface modification of graphite using ion beam doping is useful for micro-orientation control of organic thin films.
calculationsShimoyama, Iwao; Baba, Yuji
DV-X Kenkyu Kyokai Kaiho, 28(1&2), p.62 - 69, 2016/03
We studied electronic structures at phosphorus sites doped in graphite to clarify the dopant effect on catalytic activity of P-doped graphite using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A sample prepared by high-temperature doping at 700 
C showed graphite-like clear polarization dependence of P K-edge NEXAFS spectra indicating planar structure at phosphorus sites. We calculated electronic structures at phosphorus sites in carbon model clusters using the DV-X method and compare them with NEXAFS. The electronic structure at planar phosphorus site with three carbon coordination reproduced the NEXAFS spectra. On the other hand, samples prepared by room-temperature doping and post annealing at 800 C showed deterioration of polarization dependence of NEXAFS. We clarified that an electronic structure of a curved carbon model cluster with a pentagon reproduced change of polarization dependence and spectral shape of NEXAFS. This means local structures at phosphorus sites can be controlled by substrate temperatures during ion dopings.
Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro
DV-X Kenkyu Kyokai Kaiho, 27(1&2), p.34 - 44, 2015/03
no abstracts in English
-BN thin film on Ni(111) using NEXAFS spectroscopyShimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Nath, K. G.
Hyomen Kagaku, 25(9), p.555 - 561, 2004/09
no abstracts in English
Tanaka, Masahito*; Nakagawa, Kazumichi*; Koketsu, Toshiyuki*; Agui, Akane; Yokoya, Akinari
Journal of Synchrotron Radiation, 8(Part2), p.1009 - 1011, 2001/03
Amino acid molecules are known to be in the state of so-called "zwitter-ion" in solid phase and its extremely low vapour pressure makes ultra high vacuum experiment such as the XANES experiment possible. Recently, C-K edge XANES spectra of aromatic amino acids were studied experimentally and theoretically. Here we selected oxygen K-edge for XANES study of amino acids. From the view point of K-edge XANES study in amino acids, oxygen is interesting because its chemical states have the wealth of variety. A carboxylic group on the carbon is in the state of carboxylic anion -COO-, while carboxylic group in side-chain stays on -COOH, and some amino acids have -OH group in side-chain. Due to this variety of chemical environment, we can expect characteristic chemical shift for each oxygen atom in various amino acids. In this paper, we report a result of oxygen K-edge XANES spectra of amino acids (glycine, L-a-alanine, b-alanine, L-serine, L-asparic acid and L-tyrosine) films. We discuss the details of spectra on the basis of DV-X calculation.
; *
Journal of Electron Spectroscopy and Related Phenomena, 19(3), p.261 - 271, 1980/00
no abstracts in English
Shimoyama, Iwao; Baba, Yuji; Hirao, Norie*
no journal, ,
Polydimethylsilane (PDMS) is expected as one-dimensional electronic and optical devices. We studied orientation of PDMS thin films on highly oriented pyrolytic graphite (HOPG) irradiated by ion beams. We irradiated N
ions with an acceleration energy of 3 keV on a HOPG substrate and deposited a PDMS film on the substrate. We calculated electronic structure of PDMS thin film using DV-X molecular orbital calculations to interpret near edge X-ray absorption fine structure (NEXAFS) spectra of a PDMS thin film deposited on a non irradiated HOPG substrate. Based on the polarization dependence of Si -edge NEXAFS spectra, we clarified that the PDMS film had flat-lying orientation on the non irradiated substrate. Meanwhile, NEXAFS spectra showed that PDMS films had random orientation on an Ar-irradiated substrate and up-right standing orientation on N-irradiated, respectively. These results suggest new micro orientation control method for organic devices using ion doping.
Shimoyama, Iwao; Baba, Yuji*
no journal, ,
Cs-free mineralization enable soil decontamination at lower temperature than conventional heat treatments because Cs is removed through conversion of clay minerals to different minerals, but the efficiency depends on additives. CaCl derives high decontamination ratio accompanying phase transformation of clay minerals at 700C, however, the effect of Cl is unclear. In this work, Cs-sorbed weathered biotite (Cs-WB) was used as a model soil, and the interaction between Cl and Cs-WB before phase transformation was investigated using NEXAFS spectroscopy. Cs-WB was reacted with NaCl-CaCl and excessive salt was removed by water rinsing. NEXAFS spectrum of the sample prepared at 400C showed three kind of Cl sites which are attributed to -1, +1, and high valencies based on the DV-X molecular orbital calculations. Because +1 and high valence Cl sites with Cl-O bonding destabilize silica framework, this interaction can facilitate decomposition of clay minerals at moderate temperatures. The comparison of other chloride reagents suggests that the effect of Cl depends on the valence of counter cation in the reagent.
; Effect of chlorine on phase transformation of a clay mineralShimoyama, Iwao
no journal, ,
Radiocesium-contaminated soil is a severe unsolved problem in environmental remediation of Fukushima. Cesium-free mineralization (CFM) is a soil decontamination method by heating, and the characteristics of CFM is that Cs is removed by converting clay minerals which fix Cs in soil to other minerals through chemical reactions. CFM has succeeded Cs removal from weathered biotite (WB) at much lower temperature (700C) with CaCl reactant than conventional heat treatments. By contrast, phase transformation of WB did not occur at the temperature with Ca(OH) and CaCO
reactants, which suggests some effect of Cl for phase transformation, however, the detail is unclear. The interaction between Cl and WB was studied using X-ray absorption spectroscopy. The Cl spectrum of the sample prepared at 400C with CaCl showed multiple components which are interpreted as negative monovalent, positive monovalent, and positive high-valent Cl sites based on molecular orbital (MO) calculations. Comparison of structural stability of some silica model clusters by MO calculations indicates that formation of O-Cl bonds destabilizes the system more efficiently than formation of Si-Cl bonds. These results suggest that O-Cl bonds destabilize clay minerals and facilitates phase transformation of clay minerals at lower temperatures.
