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121 results on '"Azuma, Junpei"'

1. Two-Dimensional Band Dispersion of Ultra-Flat Hexagonal Bismuthene Grown on Ag(111) Bulk and Quantum-Well Films

Author

Takahashi, Kazutoshi, Imamura, Masaki, Ikeda, Haruto, Koyama, Ryosuke, Yamamoto, Isamu, and Azuma, Junpei

Subjects
Condensed Matter - Materials Science
Abstract

Two-dimensional band dispersion of (2$\times$2) superstructure with Bi grown on Ag(111), which has been urged as an ultraflat hexagonal bismuthene, is investigated using angle-resolved photoemission spectroscopy (ARPES). The (2$\times$2)-Bi superstructure can be grown on the Ag(111) surface at low temperatures; it transforms into a surface alloy with a ($\sqrt{3}\times\sqrt{3}$) superstructure at 300 K. ARPES measurements reveal the consistency with the band structure of ultraflat bismuthene in previous reports. The band structure of (2$\times$2)-Bi surface remains unchanged with decreasing Ag layer thickness, indicating the limited penetration of Bi p-orbitals into the Ag layer., Comment: 6 pages, 4 figures

Published
2023
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3. One-dimensionality of the spin-polarized surface conduction and valence bands of quasi-one-dimensional Bi chains on GaSb(110)-(2$\times$1)

Author

Ohtsubo, Yoshiyuki, Tokumasu, Naoki, Watanabe, Hiroshi, Nakamura, Takuto, Fèvre, Patrick Le, Bertran, François, Imamura, Masaki, Yamamoto, Isamu, Azuma, Junpei, Takahashi, Kazutoshi, and Kimura, Shin-ichi

Subjects
Condensed Matter - Materials Science
Abstract

Surface electronic structure and its one-dimensionality above and below the Fermi level ($E_{\rm F}$) were surveyed on the Bi/GaSb(110)-(2$\times$1) surface hosting quasi-one-dimensional (Q1D) Bi chains, using conventional (one-photon) and two-photon angle-resolved photoelectron spectroscopy (ARPES) and theoretical calculations. ARPES results reveal that the Q1D electronic states are within the projected bulk bandgap. Circular dichroism of two-photon ARPES and density-functional-theory calculation indicate clear spin and orbital polarization of the surface states consistent with the giant sizes of Rashba-type SOI, derived from the strong contribution of heavy Bi atoms. The surface conduction band above $E_{\rm F}$ forms a nearly straight constant-energy contour, suggesting its suitability for application in further studies of one-dimensional electronic systems with strong SOI. A tight-binding model calculation based on the obtained surface electronic structure successfully reproduces the surface band dispersions and predicts possible one- to two-dimensional crossover in the temperature range of 60--100~K., Comment: 18 pages, 6 figures and 2 tables

Published
2020
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6. Self-trapped electrons and holes in PbBr$_2$ crystals

Author

Iwanaga, Masanobu, Azuma, Junpei, Shirai, Masanobu, Tanaka, Koichiro, and Hayashi, Tetsusuke

Subjects
Condensed Matter - Materials Science
Abstract

We have directly observed self-trapped electrons and holes in PbBr$_{2}$ crystals with electron-spin-resonance (ESR) technique. The self-trapped states are induced below 8 K by two-photon interband excitation with pulsed 120-fs-width laser light at 3.10 eV. Spin-Hamiltonian analyses of the ESR signals have revealed that the self-trapping electron centers are the dimer molecules of Pb$_2$$^{3+}$ along the crystallographic a axis and the self-trapping hole centers are those of Br$_2$$^-$ with two possible configurations in the unit cell of the crystal. Thermal stability of the self-trapped electrons and holes suggests that both of them are related to the blue-green luminescence band at 2.55 eV coming from recombination of spatially separated electron-hole pairs., Comment: 8 pages (7 figures, 2 tables), ReVTEX; revised the text and figures 1, 4, and 5

Published
2002
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18. One-dimensionality of the spin-polarized surface conduction and valence bands of quasi-one-dimensional Bi chains on GaSb(110)-( 2×1 )

Author

Ohtsubo, Yoshiyuki, primary, Tokumasu, Naoki, additional, Watanabe, Hiroshi, additional, Nakamura, Takuto, additional, Le Fèvre, Patrick, additional, Bertran, François, additional, Imamura, Masaki, additional, Yamamoto, Isamu, additional, Azuma, Junpei, additional, Takahashi, Kazutoshi, additional, and Kimura, Shin-ichi, additional

Published
2020
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21. Surface photo-voltage effect on Cr/GaAs(100) studied by photoemission spectroscopy with the combination of synchrotron radiation and laser.

Author

Takahashi, Kazutoshi, Tokudomi, Sinji, Nagata, Yusuke, Azuma, Junpei, and Kamada, Masao

Subjects
PHOTOELECTRON spectroscopy, GALLIUM arsenide, CHROMIUM, PHOTOEMISSION, LASERS
Abstract

The surface photo-voltage (SPV) effect and its temporal profile on a Cr/p-GaAs(100) surface were measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. It was found that the SPV value at the Cr thickness of 0.05 and 0.1 nm is enhanced in comparison with the clean surface, while that at the Cr thickness larger than 0.2 nm is remarkably suppressed. The dependence on the Cr thickness can be interpreted in terms of the change in the band bending and the escape process, which are associated with the electronic structures induced by the Cr deposition. [ABSTRACT FROM AUTHOR]

Published
2011
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22. Photoelectron spectroscopic study on the electronic structures of the dental gold alloys and their interaction with L-cysteine.

Author

Ogawa, Koji, Tsujibayashi, Toru, Takahashi, Kazutoshi, Azuma, Junpei, Ichimiya, Masayoshi, Fujimoto, Hitoshi, Sumimoto, Michinori, and Kamada, Masao

Subjects
PHOTOELECTRON spectroscopy, ALLOYS, ELECTRONIC structure, MOLECULAR spectroscopy, THICK films, SURFACES (Technology), PARTICLES (Nuclear physics)
Abstract

The valence electronic structures of the dental gold alloys, type 1, type 3, and K14, and their interaction with L-cysteine have been studied by ultraviolet photoelectron spectroscopy with synchrotron radiation. It was found that the electronic structures of the type-1 and type-3 dental alloys are similar to that of polycrystalline Au, while that of the K14 dental alloy is much affected by Cu. The peak shift and the change in shape due to alloying are observed in all the dental alloys. It is suggested that the new peak observed around 2 eV for the L-cysteine thin films on all the dental alloys may be due to the bonding of S 3sp orbitals with the dental alloy surfaces, and the Cu-S bond, as well as the Au-S and Au-O bonds, may cause the change in the electronic structure of the L-cysteine on the alloys. [ABSTRACT FROM AUTHOR]

Published
2011
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28. Defect-Free Nanocrystals: Impurity-Induced First-Order Phase Transitions in Highly Crystalline V2O3Nanocrystals (Adv. Mater. Interfaces 12/2015)

Author

Ishiwata, Yoichi, primary, Takahashi, Eiko, additional, Akashi, Kenta, additional, Imamura, Masaki, additional, Azuma, Junpei, additional, Takahashi, Kazutoshi, additional, Kamada, Masao, additional, Ishii, Hirofumi, additional, Liao, Yen-Fa, additional, Tezuka, Yasuhisa, additional, Inagaki, Yuji, additional, Kawae, Tatsuya, additional, Nishio-Hamane, Daisuke, additional, Nantoh, Masashi, additional, Ishibashi, Koji, additional, and Kida, Tetsuya, additional

Published
2015
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29. Impurity-Induced First-Order Phase Transitions in Highly Crystalline V2O3Nanocrystals

Author

Ishiwata, Yoichi, primary, Takahashi, Eiko, additional, Akashi, Kenta, additional, Imamura, Masaki, additional, Azuma, Junpei, additional, Takahashi, Kazutoshi, additional, Kamada, Masao, additional, Ishii, Hirofumi, additional, Liao, Yen-Fa, additional, Tezuka, Yasuhisa, additional, Inagaki, Yuji, additional, Kawae, Tatsuya, additional, Nishio-Hamane, Daisuke, additional, Nantoh, Masashi, additional, Ishibashi, Koji, additional, and Kida, Tetsuya, additional

Published
2015
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