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Journal Articles

Quasi-one-dimensional magnetic interactions and conduction electrons in EuCu$$_5$$ and EuAu$$_5$$ with the characteristic hexagonal structure

Matsuda, Shinya*; Ota, Joji*; Nakaima, Kenri*; Iha, Wataru*; Gochi, Jun*; Uwatoko, Yoshiya*; Nakashima, Miho*; Amako, Yasushi*; Honda, Fuminori*; Aoki, Dai*; et al.

Philosophical Magazine, 100(10), p.1244 - 1257, 2020/04

 Times Cited Count:3 Percentile:37.52(Materials Science, Multidisciplinary)

Journal Articles

Characterization of F$$^{+}$$-irradiated graphite surfaces using photon-stimulated desorption spectroscopy

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.

Surface and Interface Analysis, 38(4), p.352 - 356, 2006/04

 Times Cited Count:3 Percentile:7.57(Chemistry, Physical)

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 $$sim$$689.4 eV assigned as a $$sigma$$*(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$$^{2+}$$- PSID NEXAFS spectra are helpful in understanding desorption mechanism, thus in analysing NEXAFS data.

Journal Articles

Mechanism of state-specific enhancement in photon-stimulated desorption as studied using a polarization-dependent technique

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Wu, G.*; Kitajima, Yoshinori*

Surface Science, 593(1-3), p.310 - 317, 2005/11

 Times Cited Count:2 Percentile:12.09(Chemistry, Physical)

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.

Journal Articles

Direct and indirect processes in photon-stimulated ion desorption from condensed formamide

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro; Baba, Yuji; Imamura, Motoyasu*; Matsubayashi, Nobuyuki*; Shimada, Hiromichi*

Surface Science, 593(1-3), p.303 - 309, 2005/11

 Times Cited Count:5 Percentile:26.91(Chemistry, Physical)

no abstracts in English

Journal Articles

Substitution effect on orientation of organosilicon compounds (CH$$_{3}$$)$$_{3}$$SiX (X = F, Cl, Br, I, NCO) as studied using NEXAFS spectroscopy

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.*; Uddin, M. N.*

Journal of Physics; Condensed Matter, 17(36), p.5453 - 5466, 2005/09

 Times Cited Count:1 Percentile:6.49(Physics, Condensed Matter)

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$$_{3}$$)$$_{3}$$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.

Journal Articles

Time-resolved X-ray diffraction study on surface structure and morphology during molecular beam epitaxy growth

Takahashi, Masamitsu; Yoneda, Yasuhiro; Inoue, Hirotane*; Yamamoto, Naomasa*; Mizuki, Junichiro

Journal of Crystal Growth, 251(1-4), p.51 - 55, 2003/04

 Times Cited Count:3 Percentile:22.69(Crystallography)

The reflection high energy electron diffraction (RHEED) oscillation has been widely adopted for studies on growth kinetics and dynamics in molecular beam epitaxy (MBE). Recent development in brilliant X-ray source has enabled similar experiments with X-rays, which has great advantage in a straightforward interpretation of results and in a high angular resolution. In general, the diffracted intensity from surface is proportional to the surface structure factor associated with the surface reconstruction, F, multiplied by a damping factor associated with the surface roughness, m. We show that the two factors, F and m, can be obtained separately by measuring diffuse scattering around the two-dimensional Bragg peak during growth.

Journal Articles

RHEED observation of BaTiO$$_3$$ thin films grown by MBE

Yoneda, Yasuhiro; Sakaue, Kiyoshi*; Terauchi, Hikaru*

Surface Science, 529(3), p.283 - 287, 2003/04

 Times Cited Count:8 Percentile:43.7(Chemistry, Physical)

Ferroelectric BaTiO$$_3$$ thin filmwith a thickness of 10ML were epitaxally grown on SrTiO$$_3$$ (001) substrate by very slow deposition using MBE. The investigation were carried out by two growth methods: (i) codeposition and (ii) alternate deposition. In-situ observation of RHEED confirmed that an epitaxial cube-on-cube structure was prepared. After the deposition, X-ray diffraction measurements were carried out. The 10-ML-thick BaTiO$$_3$$ films were highly ${it c}$-axis oriented single crystals with good film quality.

Journal Articles

High-quality epitaxial TiO$$_{2}$$ thin films grown on $$alpha$$-Al$$_{2}$$O$$_{3}$$ substrates by pulsed laser deposition

Shinohara, Ryuji*; Yamaki, Tetsuya; Yamamoto, Shunya; Ito, Hisayoshi; Asai, Keisuke*

Journal of Materials Science Letters, 21(12), p.967 - 969, 2002/06

 Times Cited Count:9 Percentile:37.73(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Preparation of epitaxial TiO$$_{2}$$ films by PLD for photocatalyst applications

Yamaki, Tetsuya; Sumita, Taishi; Yamamoto, Shunya; Miyashita, Atsumi

Journal of Crystal Growth, 237-239(Part1), p.574 - 579, 2002/04

Pulsed laser deposition (PLD) with a KrF excimer laser was used to prepare epitaxial TiO$$_{2}$$ films on a (0001) sapphire substrate. The crystalline structure and surface morphology of the films were then investigated as a function of the laser power density in the PLD. X-ray diffraction and Raman spectroscopy results showed that the films were composed of the (100) oriented rutile phase with a small amount of the (001) oriented anatase. The anatase-to-rutile ratio in such phase-mixed films was controlled by the laser power; the ratio increased as the power density decreased. From atomic force microscopy observations, the film deposited at the lowest power was found to have a rough surface consisting of coarse grains. This film exhibited the best photocatalytic performance during the decomposition of the organic dyes possibly due to the maximum relative content of anatase and the large surface area.

Journal Articles

Present status of the study on radionuclide diffusion in barrier materials

Yamaguchi, Tetsuji; Nakayama, Shinichi

JAERI-Conf 2002-004, p.325 - 332, 2002/03

When long-lived radionuclides are transported by groundwater through fractures in the rock mass surrounding a radioactive waste repository, their diffusion into pores in the rock matrix and ensuing sorption onto mineral surfaces are expected to retard their transport along the pathways. We have characterized the pore structure of the Japanese Inada biotite granite and confirmed that Fick's diffusion law can be applied to the transport of aqueous species in granite. Effective diffusivity was determined by the through-diffusion method for cationic, anionic and actinide complex species to explore the mechanism of diffusion of the aqueous species. The results of this study enable us to provide a scientifically sound basis for radionuclide diffusion in granite for performance assessment of geological disposal. Future studies should emphasize understanding the diffusion mechanisms in low-permeability engineered barrier materials, data acquisition on long-term degradation of the materials and quantifying uncertainties associated with long-term mass transport analysis.

Journal Articles

Surface structure of laser ablated C$$_{60}$$ pellet

Yoda, Osamu; Miyashita, Atsumi

Journal of Applied Physics, 75(10), p.5450 - 5452, 1994/05

 Times Cited Count:1 Percentile:11.43(Physics, Applied)

no abstracts in English

JAEA Reports

Dynamic behaviors of fragments ejected from the surface of carbon materials by laser ablation

Yoda, Osamu; Miyashita, Atsumi; *; *

JAERI-M 92-173, 27 Pages, 1992/10


no abstracts in English

JAEA Reports

Stress Intensity Factor Analyses of Surface Cracks in Three-Dimensional Structures

*; ; *; *

JAERI-M 83-189, 44 Pages, 1983/11


no abstracts in English

Oral presentation

Surface alternation of Cr$$_{2}$$O$$_{3}$$-CoO-Al$$_{2}$$O$$_{3}$$-doped iron-phosphate glasses containing fission products during immersion in water and heating in vacuum

Yano, Tetsuji*; Tateno, Hayato*; Kishi, Tetsuo*; Okita, Takeshi*; Matsuyama, Kanae*; Miyamoto, Shinya*; Kofuji, Hirohide; Myochin, Munetaka

no journal, , 

Oral presentation

Edge structures of montmorillonite; A Density functional theory study

Sakuma, Hiroshi*; Tachi, Yukio; Yotsuji, Kenji; Kawamura, Katsuyuki*

no journal, , 

Clay minerals are good adsorbents of many toxic elements of molecules in natural environment, because of their large surface areas and their high affinity to organic and inorganic materials. The adsorption sites of ions and molecules on the basal planes can be estimated by experiments and computer simulations based on the simple surface structure. While the adsorption of ions and molecules on the edge planes of clay minerals is poorly understood due to the absence of established model of the edge structures. In this study, the edge structures of montmorillonite were examined by the first-principles calculations based on the density functional theory. The effect of isomorphous substitution, layer charge, and positions of interlayer cations was evaluated for four different edge planes by calculating the surface energy. The acidity constant of the edges were calculated by an empirical method. We will discuss possible adsorption sites of cations on these edges.

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