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Journal Articles

Absorbent property of fullerene for cesium isotope separation investigated using X-ray photoelectron spectroscopy

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 ($$^{135}$$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$$_{60}$$) 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$$_{60}$$ 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 ${AA}$.

Journal Articles

STM-induced SiO$$_{2}$$ decomposition on Si(110)

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

Journal Articles

Characterization of SiO$$_{2}$$ reduction reaction region at void periphery on Si(110)

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:13.43(Physics, Applied)

Journal Articles

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

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:27.64(Physics, Applied)

Journal Articles

Stress evolution during Si(111)7$$times$$7 surface reconstruction

Asaoka, Hidehito; Uozumi, Yuki

Hyomen Kagaku, 37(9), p.446 - 450, 2016/09

no abstracts in English

Journal Articles

Silver photo-diffusion and photo-induced macroscopic surface deformation of Ge$$_{33}$$S$$_{67}$$/Ag/Si substrate

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:10 Percentile:50.18(Physics, Applied)

Journal Articles

Processes of silver photodiffusion into Ge-chalcogenide probed by neutron reflectivity technique

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:39(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Intermetallic charge transfer in MTiO$$_{3}$$ (M = Mn, Fe, Co, and Ni) by Ti2p edge resonant inelastic X-ray scattering

Agui, Akane; Mizumaki, Masaichiro*; Uozumi, Takayuki*

Journal of Electron Spectroscopy and Related Phenomena, 205, p.106 - 110, 2015/11

 Times Cited Count:5 Percentile:34.86(Spectroscopy)

In this study, we have measured the Ti 2p edge resonant inelastic X-ray scattering spectra of MTiO3 (M= Mn, Fe, Co, and Ni) in order to investigate the intermetallic M 3d-Ti 3d charge transfer. We found the peak around -4.5 eV in the energy loss scale for all MTiO$$_{3}$$ and additionally found that only FeTiO$$_{3}$$ has a peak at at -2.5 eV. Those peaks are attributed to the M 3d-Ti 3d charge transfer.

Journal Articles

Measurement of transient photo-induced changes in thin films at J-PARC; Time-resolved neutron reflectivity measurements of silver photo-diffusion into Ge-chalcogenide films

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 Ge$$_{x}$$S$$_{1-x}$$ (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.

Journal Articles

Surface stress measurement of Si(111) 7$$times$$7 reconstruction by comparison with hydrogen-terminated 1$$times$$1 surface

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 7$$times$$7 reconstruction by comparison with the hydrogen (H)-terminated Si(111) 1$$times$$1 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) 7$$times$$7 surface. After the above treatment, a complete transformation of the surface structure occurs from the reconstructed surface to the 1$$times$$1 one. As a result, we find the H-terminated Si(111) 1$$times$$1 surface releases 1.7 N/m (=J/m$$^{2}$$), or (1.4 eV/(1$$times$$1 unit cell)), of the surface energy from the strong tensile Si(111) 7$$times$$7 reconstruction.

Journal Articles

Dynamics of silver photo-diffusion into Ge-chalcogenide films; Time-resolved neutron reflectometry

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:96.8

We report the results of time-resolved neutron reflectivity measurements of Ag/a- Ge$$_{20}$$S$$_{80}$$/Si and a- Ge$$_{40}$$Se$$_{60}$$/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-Ge$$_{20}$$S$$_{80}$$/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-Ge$$_{40}$$Se$$_{60}$$/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.

Journal Articles

Electronic structure of BaFeO$$_{3}$$ studied by X-ray spectroscopy

Mizumaki, Masaichiro*; Fujii, Hitoshi*; Yoshii, Kenji; Hayashi, Naoaki*; Saito, Takashi*; Shimakawa, Yuichi*; Uozumi, Takayuki*; Takano, Mikio*

Physica Status Solidi (C), 12(6), p.818 - 821, 2015/06

 Times Cited Count:8 Percentile:94.79

We investigated the electronic structure of BaFeO$$_{3}$$ by using HAXPES and XAS measurements and first principle studies. The experimental and theoretical results indicated that BaFeO$$_{3}$$ is a negative charge transfer compound. We concluded that the on-site Coulomb energy and the strong hybridization between Fe-3d and O-2p orbitals play a very important role of emergence of negative charge transfer. And we found the new structure in the Fe-2p XPS spectrum and concluded this structure is originated from non-local screening.

Journal Articles

Temperature and polarization dependence of Fe L$$_{3}$$-edge X-ray absorption spectra of LuFe$$_{2}$$O$$_{4}$$

Agui, Akane; Mizumaki, Masaichiro*; Kuroda, Tomoko*; Kawai, Masahiro*; Nagata, Tomoko*; Ikeda, Naoshi*; Uozumi, Takayuki*

Journal of Electron Spectroscopy and Related Phenomena, 197, p.13 - 16, 2014/12

 Times Cited Count:4 Percentile:27.92(Spectroscopy)

In this paper, we report on the study of the temperature dependence of Fe L$$_{3}$$-edge X-ray absorption spectra (XAS) of LuFe$$_{2}$$O$$_{4}$$. In the charge ordered state the valence of Fe is in Fe$$^{2+}$$ and Fe$$^{3+}$$. And the Fe L$$_{3}$$-edge XAS spectra have double peak structure which is attributed the Fe$$^{2+}$$ and Fe$$^{3+}$$ state. In high temperature, the double peak structure becomes indistinct because the thermal excited state overlaps while the Fe valence keeping the integer number.

Journal Articles

Unique surface structure formation on a Ge-covered Si(110)-16$$times$$2 surface

Yokoyama, Yuta*; Uozumi, Yuki; Asaoka, Hidehito

Journal of Crystal Growth, 405, p.35 - 38, 2014/11

 Times Cited Count:1 Percentile:13.09(Crystallography)

Si-Ge structures forming new shapes on a Si(110)-16$$times$$2 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)-16$$times$$2 surface, single-domain of 16$$times$$2 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.

Journal Articles

Studies of silver photo diffusion dynamics in Ag/Ge$$_{x}$$S$$_{1-x}$$ ($$x$$=0.2 and 0.4) films using neutron reflectometry

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:65.16(Physics, Multidisciplinary)

We report our recent results of neutron reflectivity measurements for Ag/a-Ge $$_{x}$$S$$_{1-x}$$ (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 $$_{40}$$S $$_{60}$$ 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 $$_{40}$$S $$_{60}$$ layer in terms of Ag composition, and the next silver diffusion process occurs by affecting the Ag-doped Ge $$_{40}$$S $$_{60}$$ layer / interface. This coincides with the Ge $$_{40}$$S $$_{60}$$ 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.

Journal Articles

Intermetallic charge transfer in FeTiO$$_{3}$$ probed by resonant inelastic soft X-ray scattering

Agui, Akane; Uozumi, Takayuki*; Mizumaki, Masaichiro*; K$"a$$"a$mbre, T.*

Physical Review B, 79(9), p.092402_1 - 092402_4, 2009/03

AA2008-0923.pdf:0.24MB

 Times Cited Count:18 Percentile:61.44(Materials Science, Multidisciplinary)

We studied the electronic structure of FeTiO$$_{3}$$. The experimental technique used in this study was Ti 2$$p$$ soft resonant X-ray inelastic scattering spectroscopy (RIXS) and it was carried out at I511-3 at MAX-lab. FeTiO$$_{3}$$ has the ilmenite structure and this is an ordered corundum structure. Ions of Fe and Ti occupy the basal cation planes alternatively in which Fedivalent and Ti is tetravalent. Local symmetry around transition metal ions, both Fe and Ti, are in the distorted Oh symmetry. Butorin et al had reported the RIXS spectra of Ti La,b (Phy. Rev. B55 (1997) 4242) in the 3$$d$$$$^{0}$$ compounds and discussed the charge-transfer transitions from Ti 3$$d$$ - O 2$$p$$ hybridization. In this study, we measured Ti La,b RIXS of FeTiO$$_{3}$$ in detail and the spectra shows rich resonant feature. When the excitation energy is tuned at the well-defined $$e$$$$_{g}$$ peak of Ti L3 X-ray absorption spectrum (XAS), a clear small peak appears at 2.5 eV below from the elastic peak. An additional peak comes up at 4.5 eV below the elastic peak when the excitation energy is tuned at the well defined $$t$$$$_{2g}$$ peak of XAS. The spectral features are attributed to eg and $$t$$$$_{2g}$$ state of Ti 3$$d$$ due to crystal field and charge transfer between Ti 3$$d$$ and O 2$$p$$. We are analyzing the RIXS spectra within the cluster model in order to investigate the clear resonant peaks. By demonstrating a double-cluster model calculation taking into account offull-multiplet, we conclude that the origin of features are attributed to Fe 3$$d$$ $$rightarrow$$ Ti 3$$d$$ charge transfer process with $$d$$-$$d$$ charge transfer form Fe to Ti, e.g. it is due to inter-metallic charge transfer, which is a new essential elementary optical process in RIXS study.

Journal Articles

Admixture of excited states and ground states of a Eu$$^{3+}$$ ion in Eu$$_{3}$$Fe$$_{5}$$O$$_{12}$$ by means of magnetic circular dichroism

Mizumaki, Masaichiro*; Uozumi, Takayuki*; Agui, Akane; Kawamura, Naomi*; Nakazawa, Makoto*

Physical Review B, 71(13), p.134416_1 - 134416_8, 2005/04

 Times Cited Count:14 Percentile:53.16(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Theoretical and experimental study of resonant $$3d$$ X-ray photoemission and resonant $$L_{3}M_{45}M_{45}$$ Auger transition of PdO

Uozumi, Takayuki*; Okane, Tetsuo; Yoshii, Kenji; Sasaki, Teikichi; Kotani, Akio*

Journal of the Physical Society of Japan, 69(4), p.1226 - 1233, 2000/04

 Times Cited Count:8 Percentile:53.49(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Cluster model calculations for the Fe L$$_{2,3}$$-edge fine structure of $$alpha$$-Fe$$_{2}$$O$$_{3}$$

Kurata, Hiroki; Hojo, Kiichi; Uozumi, Takayuki*

Journal of Electron Microscopy, 47(4), p.293 - 299, 1998/00

 Times Cited Count:4 Percentile:17.64(Microscopy)

no abstracts in English

Oral presentation

The Origin of the excited states in Eu$$^{3+}$$ ions

Mizumaki, Masaichiro*; Agui, Akane; Yoshii, Kenji; Uozumi, Takayuki*

no journal, , 

no abstracts in English

63 (Records 1-20 displayed on this page)