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Sekiguchi, Tetsuhiro; Yokoyama, Keiichi; Uozumi, Yuki*; Yano, Masahiro; Asaoka, Hidehito; Suzuki, Shinichi; Yaita, Tsuyoshi
Progress in Nuclear Science and Technology (Internet), 5, p.161 - 164, 2018/11
For nuclear transmutation of cesium-135 (Cs), which is long-lived fission product, we are developing selective absorbent which takes only Cs atom in, but does not CsI. In this study, absorbing property of Cs atom onto the surface of fullerene (C) film has been investigated using synchrotron-based angle-dependent X-ray photoelectron spectroscopy (XPS). The results were compared with those of CsI. It was found that Cs penetrates into C deep bulk. In contrast, CsI deposits on shallow surface. Furthermore, XPS spectra were measured as a function of Ar-sputtering time in order to know Cs concentration profiles in deep region. Results showed that Cs penetrates into deep region of several hundreds .
Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito; Tsukada, Chie*; Yoshida, Hikaru*; Yoshigoe, Akitaka
e-Journal of Surface Science and Nanotechnology (Internet), 16, p.370 - 374, 2018/08
Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Tsukada, Chie*; Yoshida, Hikaru*; Yoshigoe, Akitaka; Asaoka, Hidehito
Japanese Journal of Applied Physics, 57(8S1), p.08NB13_1 - 08NB13_4, 2018/07
Times Cited Count:2 Percentile:9.42(Physics, Applied)Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito
Japanese Journal of Applied Physics, 57(6S1), p.06HD04_1 - 06HD04_4, 2018/06
Times Cited Count:4 Percentile:20.17(Physics, Applied)Asaoka, Hidehito; Uozumi, Yuki
Hyomen Kagaku, 37(9), p.446 - 450, 2016/09
no abstracts in English
Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kondo, Keietsu; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Mitkova, M.*
Journal of Applied Physics, 120(5), p.055103_1 - 055103_10, 2016/08
Times Cited Count:11 Percentile:46.95(Physics, Applied)Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Sheoran, G.*; Mitkova, M.*
Physica Status Solidi (A), 213(7), p.1894 - 1903, 2016/07
Times Cited Count:7 Percentile:34.12(Materials Science, Multidisciplinary)no abstracts in English
Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Wolf, K.*; et al.
JPS Conference Proceedings (Internet), 8, p.031023_1 - 031023_6, 2015/09
We report recent results of time-resolved neutron reflectivity measurements for silver photo-diffusion into GeS (x=0.20, 0.33, 0.40) films performed on BL17 (SHARAKU). It is well known that silver diffuses into Ge-chalcogenide layer by visible light exposure with a distinct diffusion front, where the silver concentration abruptly drops off. Using an event recording system at the Materials and Life Science Experimental Facility, neutron reflectivity profiles were collected with a time-resolution of 30 seconds in the shortest case. It was found from the measurements that a relatively stable Ag-rich phase in the reaction layer is firstly formed, and then, slower diffusion occurs at the interface between Ag-rich and Ag-poor layers. Fourier transform analysis showed that the position of the interface is essentially fixed. This result is in contrast to the previously reported model of silver diffusion that postulates a mechanism involving progression of the diffusion front. The results of the measurements on Ag/Ge-Se films performed on the INTER instrument at ISIS are also reported.
Asaoka, Hidehito; Uozumi, Yuki
Thin Solid Films, 591(Part B), p.200 - 203, 2015/09
We have focused on measurements of the surface stress in Si(111) as a function of 77 reconstruction by comparison with the hydrogen (H)-terminated Si(111) 11 surface. In order to obtain information on both the surface stress and the surface reconstruction simultaneously, we have combined the surface-curvature and the reflection-high-energy-electron-diffraction instrumentations in an identical ultrahigh vacuum system. The stress evolution shows a decrease of tensile stress corresponding to the formation of H-termination at the beginning of the atomic H exposure of Si(111) 77 surface. After the above treatment, a complete transformation of the surface structure occurs from the reconstructed surface to the 11 one. As a result, we find the H-terminated Si(111) 11 surface releases 1.7 N/m (=J/m), or (1.4 eV/(11 unit cell)), of the surface energy from the strong tensile Si(111) 77 reconstruction.
Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Latif, M. R.*; et al.
Journal of Physics; Conference Series, 619(1), p.012046_1 - 012046_4, 2015/06
Times Cited Count:8 Percentile:95.66(Engineering, Electrical & Electronic)We report the results of time-resolved neutron reflectivity measurements of Ag/a- GeS/Si and a- GeSe/Ag/ Si films taken while the films are exposed to visible light. Silver diffuses into an amorphous (a-) chalcogenide layer while visible light illuminates Ag/a-chalcogenide films. Neutron reflectometry is a suitable technique probing time evolution of the multi-layer structure without damaging the sample by the probe beam itself. It was found from the measurements of Ag/a-GeS/Si films that a relatively stable Ag-rich phase in the reaction layer is first formed, and then, slower diffusion occurs at the interface between Ag-rich and Ag-poor layers. This result is in contrast to the previously reported model of silver diffusion that suggests a mechanism involving progression of the diffusion front. From the measurements of a-GeSe/Ag/ Si films, we found enormous changes in the neutron reflectivity profile, including loss of total reflection region, with continuous illumination even after forming one homogeneous layer, which was about 60 min after starting illumination. At this stage, clear off-specular scattering was observed by a linear detector and a surface roughness was observed with naked eyes.
Yokoyama, Yuta*; Uozumi, Yuki; Asaoka, Hidehito
Journal of Crystal Growth, 405, p.35 - 38, 2014/11
Times Cited Count:1 Percentile:11.68(Crystallography)Si-Ge structures forming new shapes on a Si(110)-162 reconstructed surface were investigated via scanning tunneling microscopy. Pyramidal-shaped Si-Ge nanoislands lying along the 1 1 1 directions were formed on the striped structure at Ge coverage between 3 and 6 monolayers. However, when a single monolayer of Ge was deposited on the Si(110)-162 surface, single-domain of 162 striped structure disappeared, and a new double-domain striped structure was formed over the surface along directions that differed from the 1 1 2 directions. This structure represents a new Si-Ge striped structure that forms by the mixing of Ge and Si due to high temperature annealing. These results indicate that the surface structure changes specifically with trace amounts of Ge.
Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Latif, R.*; et al.
Canadian Journal of Physics, 92(7/8), p.654 - 658, 2014/07
Times Cited Count:12 Percentile:62.3(Physics, Multidisciplinary)We report our recent results of neutron reflectivity measurements for Ag/a-Ge S (x=0.2, 0.4) films under light illumination. The neutron reflectivity measurements have been performed on a polarized neutron reflectometer (BL17, SHARAKU) at Japan Proton Accelerator Research Complex (J-PARC), Japan. By using the time-of flight instrument with intensive pulsed neutrons produced by 300kW proton beams, time evolution of the neutron reflectivity under a light illumination has been revealed, with at least 2-min time resolution. From the detailed analysis, it was found for Ag 50nm/Ge S 150nm films under a light illumination from the Ag layer side that there are two types of diffusion processes: a fast change observed in the first 10 min after illumination using a xenon lamp, which is then followed by a slow change observed after a 1 hour of additional light exposure. The result indicates that there is a comparatively stable (metastable) state in the Ag-doped Ge S layer in terms of Ag composition, and the next silver diffusion process occurs by affecting the Ag-doped Ge S layer / interface. This coincides with the Ge S results of Wagner et al. obtained for Ag/As-S films. These results are also in accord with the results reported by some of us by modeling of the Ag transport in Ge-Se glass showing the presence of slow and fast moving Ag ions. Our result demonstrated that the idea of a two-step reaction process can be applied to Ge-chalcogenide system. We also discuss illumination-side dependence and Ge-composition dependence of reaction process.
Yokoyama, Yuta; Uozumi, Yuki; Asaoka, Hidehito
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Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Mitkova, M.*
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Silver photo-diffusion is one of the attractive phenomena observed in amorphous chalcogenide films such as As2S3 and GeSe2 because of their potential applications in, for example, photo-lithography, memory devices, and fabrication of optical elements. We report the results of neutron reflectivity measuremens for silver photo-diffusion in Ag/Ge-S films under light illumination. The neutron reflectivity measurements have been performed on a polarized neutron reflectometer (BL17, SHARAKU) at Materials and Life Science Experimental Facility (MLF), Japan Proton Accerelator Research Complex (J-PARC), Japan. By using the time-of-flight instrument with intensive pulsed neutrons produced by 300kW proton beams and sophisticated event recording system, time evolution of the neutron reflectivity under a light illumination has been revealed with, at least, 2-min time resolution. The reaction rate by the light illumination is discussed based on the detailed analysis of the time-resolved neutron reflectivity results.
Asaoka, Hidehito; Uozumi, Yuki; Yokoyama, Yuta; Yamaguchi, Kenji
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Yokoyama, Yuta; Uozumi, Yuki; Asaoka, Hidehito
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Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Ailavajhala, M.*; Rizwanlatif, M.*; Mitkova, M.*
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Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Lativ, M. R.*; et al.
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Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Uozumi, Yuki; Kawakita, Yukinobu; Ito, Takayoshi*; Kubota, Masato; Yamazaki, Dai; Soyama, Kazuhiko; Ailavajhala, M.*; Latif, R.*; et al.
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Uozumi, Yuki; Yamazaki, Tatsuya*; Asaoka, Hidehito
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