Narita, Hirokazu*; Nicolson, R. M.*; Motokawa, Ryuhei; Ito, Fumiyuki*; Morisaku, Kazuko*; Goto, Midori*; Tanaka, Mikiya*; Heller, W. T.*; Shiwaku, Hideaki; Yaita, Tsuyoshi; et al.
Inorganic Chemistry, 58(13), p.8720 - 8734, 2019/07
Li, S.*; Toyoda, Masayuki*; Kobayashi, Yoshiaki*; Ito, Masayuki*; Ikeuchi, Kazuhiko*; Yoneda, Yasuhiro; Otani, Akira*; Matsumura, Daiju; Asano, Shun*; Mizuki, Junichiro*; et al.
Physica C, 555, p.45 - 53, 2018/12
-dependence of local distortions in BaFeAs and LiFeAs by X-ray PDF and XAFS methods. Although PDF data exhibit anomaly at the structure transition temperature, EXAFS data exhibit no anomaly. Data supporting the local orthorhombicity at 300 K in the tetragonal phase for BaFeAs. Arguments on the origins of the 4-fold symmetry breaking in the ground average structure of the tetragonal phase.
Okamoto, Yoshihiro; Takano, Masahide
Progress in Nuclear Science and Technology (Internet), 5, p.200 - 203, 2018/11
Chemical state of some simulated corium debris samples containing uranium (fuel), zirconium (fuel cladding), iron (structure material), calcium (cement) and lanthanides (fission products) was investigated by synchrotron radiation based extended X-ray absorption fine structure (EXAFS) analysis. The local structure of uranium for the simulated debris was classified into fluorite UO structure and C-type structure (stabilized cubic). The UZrFeCaO sample, which consists of single phase (C-type), shows slightly shorter U-O distance. It can be concluded that the sample contains pentavalent uranium. The local structure of zirconium for U-Zr-O and U-Zr-Fe-O systems was very close to tetragonal ZrO, while that of zirconium changed to CSZ (calcia stabilized cubic) by adding calcium.
Ikeura, Hiromi*; Sekiguchi, Tetsuhiro
Applied Physics Letters, 111(23), p.231605_1 - 231605_4, 2017/12
Photo-oxidative doping processes were studied for the trans-polyacetylene (PA) backbone with the -SCH side group as a chemically representative of the S-functionalized zig-zag graphene nanoribbon edge. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy indicates that photochemical reaction of S-CH with atmospheric O forms selectively oxidized products such as -S(O)CH and -SO bound to the (PA) backbone. Using the correlation between the oxidation states of sulfur and the XANES peak positions, the partial charge distribution of CHS -PA has been estimated. The results can provide some strategy for area-selective and controllable doping processes of atomic-scale molecular systems with the assistance of UV light.
Sano, Yuichi; Watanabe, So; Matsuura, Haruaki*; Nagoshi, Kohei*; Arai, Tsuyoshi*
Journal of Nuclear Science and Technology, 54(10), p.1058 - 1064, 2017/10
For effective recovery of radioactive elements by adsorbents using polymer-immobilized silica (SiO-P) supports, the microstructure of SiO-P particles impregnated with CMPO as extractants and their change with the crosslinking degree of polymer (CDP) were investigated using STXM and EXAFS analyses; further, their relation with adsorption/elution behavior was discussed. The adsorption/elution tests using adsorbents with a different CDP demonstrated that a higher CDP inhibited the elution of adsorbed metal ions from the adsorbent. The results of STXM and EXAFS analyses suggested that adsorption by CMPO proceeds through the entire area in the adsorbent and the local structure around adsorbed metal ions is similar irrespective of the CDP. Conversely, STXM analyses implied the capture of eluents such as HO by polymers with high CDP, which suppresses the prompt elution of adsorbed metal ions from the adsorbent.
Watanabe, So; Sano, Yuichi; Shiwaku, Hideaki; Yaita, Tsuyoshi; Ono, Shimpei*; Arai, Tsuyoshi*; Matsuura, Haruaki*; Koka, Masashi*; Sato, Takahiro*
Nuclear Instruments and Methods in Physics Research B, 404, p.202 - 206, 2017/08
Abe, Ryoji*; Nagoshi, Kohei*; Arai, Tsuyoshi*; Watanabe, So; Sano, Yuichi; Matsuura, Haruaki*; Takagi, Hideaki*; Shimizu, Nobutaka*; Koka, Masashi*; Sato, Takahiro*
Nuclear Instruments and Methods in Physics Research B, 404, p.173 - 178, 2017/08
Shimoyama, Iwao; Baba, Yuji; Hirao, Norie*
Applied Surface Science, 405, p.255 - 266, 2017/05
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.
Maeda, Motoki*; Narita, Hirokazu*; Tokoro, Chiharu*; Tanaka, Mikiya*; Motokawa, Ryuhei; Shiwaku, Hideaki; Yaita, Tsuyoshi
Separation and Purification Technology, 177, p.176 - 181, 2017/04
Kojima, Hiroshi*; Yoshizaki, Hiroaki*; Kaneno, Yasuyuki*; Semboshi, Satoshi*; Hori, Fuminobu*; Saito, Yuichi; Okamoto, Yoshihiro; Iwase, Akihiro*
Nuclear Instruments and Methods in Physics Research B, 372, p.72 - 77, 2016/04
NiNb and NiTa intermetallic compounds, which show the complicated lattice structures were irradiated with 16 MeV Au ions at room temperature. The X-ray diffraction measurement revealed that the lattice structure of these intermetallic compounds changed from the ordered structures to the amorphous state by the ion irradiation. The irradiation-induced amorphization caused the increase in Vickers hardness. The result was compared with our previous results for NiAl and NiV, and was discussed in terms of the intrinsic lattice structures of the samples.
Shimoyama, 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
Shimoyama, Iwao; Hakoda, Teruyuki; Shimada, Akihiko; Baba, Yuji
Carbon, 81, p.260 - 271, 2015/01
The relationship between catalytic activity and local structure at dopant sites of phosphorus-doped graphite prepared by ion implantation was studied by electrochemical measurements and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The P K-edge NEXAFS spectra of samples doped at room temperature and high temperature showed different polarization dependences, with graphite-like clear polarization dependence observed for the sample prepared by high-temperature doping. NEXAFS spectra were analyzed by density functional theory calculations to reveal the chemical-bonding states of P sites. In electrochemical measurements with an acid solution, samples with relatively small polarization dependence of NEXAFS exhibited marked catalytic activity in oxygen reduction reactions while those with larger polarization dependence showed lower catalytic activity. This indicates the influence of the configuration at dopant sites on catalytic activity and suggests that the introduction of curved structures is one way to design carbon catalysts with high catalytic activity.
Ishimatsu, Naoki*; Sata,Yusuke*; Maruyama, Hiroshi*; Watanuki, Tetsu; Kawamura, Naomi*; Mizumaki, Masaichiro*; Irifune, Tetsuo*; Sumiya, Hitoshi*
Hoshako, 28(1), p.3 - 11, 2015/01
no abstracts in English
Petorotekku, 37(5), p.329 - 333, 2014/05
no abstracts in English
Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.
Surface and Interface Analysis, 38(4), p.352 - 356, 2006/04
We investigated the orientation nature at the top-most layers of F-irradiated graphite using polarization dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy which incorporates partial electron yield (PEY) detection and photon-stimulated ion desorption (PSID) techniques. The fluorine K-edge NEXAFS spectra conducted in PEY mode show no significant dependence on polarization angles. In contrast, NEXAFS spectra recorded in F ion yield mode show enhanced yields at a feature of 689.4 eV assigned as a *(C-F) state relevant to =C-F sites, which depend on polarization angles. The C-F bonds prefer relatively tilting down the surface at the top-most layer, while the C-F bonds are randomly directed at deeper regions. We conclude that the difference in the orientation structures between the top surface and bulk is reflected in the NEXAFS recorded in the two different detection modes. It was also found that H- and F- PSID NEXAFS spectra are helpful in understanding desorption mechanism, thus in analysing NEXAFS data.
Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Wu, G.*; Kitajima, Yoshinori*
Surface Science, 593(1-3), p.310 - 317, 2005/11
Using a newly developed rotatable time-of-flight mass spectrometer(R-TOF-MS) and polarized synchrotron radiation, orientation effect on fragmentation and desorption pathways occurring at the top-most layers of molecular solids have been investigated. Reported will be polarization-angle dependencies of TOF mass spectra, high-resolution electron- and ion-NEXAFS in condensed chlorobenzene.
Ikeura, Hiromi*; Sekiguchi, Tetsuhiro; Baba, Yuji; Imamura, Motoyasu*; Matsubayashi, Nobuyuki*; Shimada, Hiromichi*
Surface Science, 593(1-3), p.303 - 309, 2005/11
no abstracts in English
Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.*; Uddin, M. N.*
Journal of Physics; Condensed Matter, 17(36), p.5453 - 5466, 2005/09
The orientation nature of multilayer organosilicon compounds has been investigated by measuring the dependence of the Si K-shell near-edge X-ray absorption fine structures (NEXAFS) on the polarization angle. Two approaches helped to elucidate the orientation mechanism: the substitution effect and the deposition-rate dependence. The orientation angles of Si-X bond axes were obtained for trimethylsilyl halides, (CH)SiX (X =F Cl Br I NCO, condensed on Cu(111) at a low (82 K) temperature: the angles are 60, 73, 61, 55, and 55 degrees with respect to the surface normal, for X =F, Cl, Br, I, and NCO, respectively. Chloride (X =Cl) produces the most parallel tilt angle. The specific orientation nature of chloride is attributed to its strong dipole moment as well as the regular tetrahedron shape of the molecule. The molecular volumes calculated verify this view. Furthermore, deposition rates are found to greatly influence the growth manner: namely, high deposition rates led to a slightly perpendicular orientation of Si-X bond axis.
Sakai, Seiji; Naramoto, Hiroshi*; Lavrentiev, V.*; Narumi, Kazumasa; Maekawa, Masaki; Kawasuso, Atsuo; Yaita, Tsuyoshi; Baba, Yuji
Materials Transactions, 46(4), p.765 - 768, 2005/04
A systematic study of the atom-level mixtures between Co and C has made possible to find a new C-based compound phase, CoC (x5). It is confirmed with the EXAFS analysis and the positron annihilation study that the polymeric structure is developed three-dimensionally by bridging two C molecules with the covalently bonded Co atom.