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347 results on '"Niibe, Masahito"'

1. Surface structure of the 3x3-Si phase on Al(111), studied by the multiple usages of positron diffraction and core-level photoemission spectroscopy

Author

Sato, Yusuke, Fukaya, Yuki, Nakano, Akito, Hoshi, Takeo, Lee, Chi-Cheng, Yoshimi, Kazuyoshi, Ozaki, Taisuke, Nakashima, Takeru, Ando, Yasunobu, Aoyama, Hiroaki, Abukawa, Tadashi, Tsujikawa, Yuki, Horio, Masafumi, Niibe, Masahito, Komori, Fumio, and Matsuda, Iwao

Subjects
Condensed Matter - Materials Science
Abstract

The structure of an Al(111)3x3-Si surface was examined by combining data from positron diffraction and core-level photoemission spectroscopy. Analysis of the diffraction rocking curves indicated that the overlayer had a flat honeycomb lattice structure. Simulations of Si core-level spectra calculated via the first-principles indicated that one of the Si atoms in the unit cell was replaced by an Al atom. The surface superstructure was thus a two-dimensional layer of Al-embedded silicene on Al(111).

Published
2024

2. Electronic topological transition of 2D boron by the ion exchange reaction

Author

Zhang, Xiaoni, Tsujikawa, Yuki, Tateishi, Ikuma, Niibe, Masahito, Wada, Tetsuya, Horio, Masafumi, Hikichi, Miwa, Ando, Yasunobu, Yubuta, Kunio, Kondo, Takahiro, and Matsuda, Iwao

Subjects
Condensed Matter - Materials Science
Abstract

We systematically investigated electronic evolutions of non-symmorphic borophene with chemical environments that were realized by the ion exchange method. Electronic structures can be characterized by the topological $Z_2$ invariant. Spectroscopic experiments and DFT calculations unveiled that a sheet of hydrogenated borophene (borophane) is the Dirac nodal loop semimetal ($Z_2=-1$), while a layered crystal of YCrB$_4$ is an insulator ($Z_2=1$). The results demonstrate the electronic topological transition by replacement of the counter atoms on the non-symmorphic borophene layer.

Published
2022

3. A novel measurement approach for near-edge x-ray absorption fine structure: continuous 2$\pi$ angular rotation of linear polarization

Author

Kudo, Yoshiki, Hirata, Yasuyuki, Horio, Masafumi, Niibe, Masahito, and Matsuda, Iwao

Subjects
Physics - Instrumentation and Detectors, Condensed Matter - Materials Science
Abstract

A new technical method is developed for soft x-ray spectroscopy of near-edge x-ray absorption fine structure (NEXAFS). The measurement is performed with continuously rotating linearly polarized light over 2$\pi$, generated by a segmented undulator. A demonstration of the rotational NEXAFS experiment was successfully made with a 2D film, showing detailed polarization-dependence in intensity of the molecular orbitals. The present approach provides varieties of technical opportunities that are compatible with the state-of-the-art experiments in nano-space and under the $operando$ condition.

Published
2021
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4. Quasi-free-standing monolayer hexagonal boron nitride on Ni

Author

Suzuki, Satoru, Haruyama, Yuichi, Niibe, Masahito, Tokushima, Takashi, Yamaguchi, Akinobu, Utsumi, Yuichi, Ito, Atsushi, Kadowaki, Ryo, Maruta, Akane, and Abukawa, Tadashi

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The electronic structure of monolayer hexagonal boron nitride grown on Ni by the diffusion and precipitation method was studied by x-ray absorption spectroscopy, emission spectroscopy, x-ray photoelectron spectroscopy and micro-ultraviolet photoemission spectroscopy. No indication of hybridization between h-BN pi and Ni 3d orbitals was observed. That is, the monolayer h-BN was found to be in the quasi-free-standing state. These results are in striking contrast to those of previous studies in which h-BN was strongly bound to the Ni surface by the orbital hybridization. The absence of hybridization is attributed to absence of a Ni(111) surface in this study. The lattice-matched Ni(111) surface is considered to be essential to orbital hybridization between h-BN and Ni.

Published
2018
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6. Characterization of Hydrogen-Free and Hydrogenated DLC Films

Author

Harigai, Toru, Imai, Takahiro, Takikawa, Hirofumi, Kaneko, Satoru, Kunitsugu, Shinsuke, Niibe, Masahito, Kanda, Kazuhiro, Kamiya, Masao, Kaneko, Satoru, editor, Aono, Masami, editor, Pruna, Alina, editor, Can, Musa, editor, Mele, Paolo, editor, Ertugrul, Mehmet, editor, and Endo, Tamio, editor

Published
2021
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15. Plasma-assisted annealing of Pt-doped rutile TiO2 nanoparticles for enhanced decomposition and bacterial inactivation under general lighting.

Author

Kawakami, Retsuo, Makino, Yuta, Yanagiya, Shin-ichiro, Shirai, Akihiro, Niibe, Masahito, and Nakano, Yoshitaka

Subjects
RUTILE, BACTERIAL inactivation, PLATINUM nanoparticles, X-ray photoelectron spectroscopy, PHOTOELECTRON spectroscopy, PHOTOCATALYSTS, OPTICAL spectroscopy
Abstract

Enhanced photocatalytic activity of rutile-based TiO2 materials under general lighting is practically desired. O2 plasma-assisted annealing (PAA) effects on Pt-doped rutile TiO2 nanoparticles were clarified along with its visible-light-driven photocatalytic activity enhancement. The PAA-treated samples were mainly analyzed using optical spectroscopy and x-ray photoelectron spectroscopy (XPS). The photocatalytic activity was assessed by decomposing methylene blue dye and inactivating Bacillus subtilis under general lighting. The PAA treatment changed the O 1s, Ti 2p, and Pt 4f spectra of XPS from those of the pristine sample. This change indicated that the PAA treatment introduced more oxygen deficiency or oxygen vacancies and more oxygen groups adsorbed on the surface. The introduced oxygen vacancies and adsorbed oxygen groups would change the band structure, which primarily narrowed the bandgap energy or broadened the valence band edge, increased the number of electron-trapping sites from the shallow to midgap levels, and enhanced the upward band-bending at the surface. The PAA-induced change in the band structure enhanced the decomposition and bacterial inactivation because it facilitated the separation and concentration of photoexcited carriers. The findings provide a new perspective on enhancing the photocatalytic activities of rutile-based TiO2 nanoparticles under general lighting. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Quenchable compressed graphite synthesized from neutron-irradiated highly oriented pyrolytic graphite in high pressure treatment at 1500 °C

Author

Niwase, Keisuke, Terasawa, Mititaka, Honda, Shin-ichi, Niibe, Masahito, Hisakuni, Tomohiko, Iwata, Tadao, Higo, YuJi, Hirai, Takeshi, Shinmei, Toru, Ohfuji, Hiroaki, Irifune, Tetsuo, Niwase, Keisuke, Terasawa, Mititaka, Honda, Shin-ichi, Niibe, Masahito, Hisakuni, Tomohiko, Iwata, Tadao, Higo, YuJi, Hirai, Takeshi, Shinmei, Toru, Ohfuji, Hiroaki, and Irifune, Tetsuo

Published
2022

38. Quenchable compressed graphite synthesized from neutron-irradiated highly oriented pyrolytic graphite in high pressure treatment at 1500 °C.

Author

Niwase, Keisuke, Terasawa, Mititaka, Honda, Shin-ichi, Niibe, Masahito, Hisakuni, Tomohiko, Iwata, Tadao, Higo, Yuji, Hirai, Takeshi, Shinmei, Toru, Ohfuji, Hiroaki, and Irifune, Tetsuo

Subjects
PYROLYTIC graphite, IRRADIATION, NEUTRON beams, METAL quenching, CRYSTAL defects
Abstract

The super hard material of “compressed graphite” (CG) has been reported to be formed under compression of graphite at room temperature. However, it returns to graphite under decompression. Neutron-irradiated graphite, on the other hand, is a unique material for the synthesis of a new carbon phase, as reported by the formation of an amorphous diamond by shock compression. Here, we investigate the change of structure of highly oriented pyrolytic graphite (HOPG) irradiated with neutrons to a fluence of 1.4 × 1024 n/m2 under static pressure. The neutron-irradiated HOPG sample was compressed to 15 GPa at room temperature and then the temperature was increased up to 1500 °C. X-ray diffraction, high-resolution transmission electron microscopy on the recovered sample clearly showed the formation of a significant amount of quenchable-CG with ordinary graphite. Formation of hexagonal and cubic diamonds was also confirmed. The effect of irradiation-induced defects on the synthesis of quenchable-CG under high pressure and high temperature treatment was discussed. [ABSTRACT FROM AUTHOR]

Published
2018
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44. Photocatalytic Activity Enhancement of Anatase/Rutile-Mixed Phase TiO2 Nanoparticles Annealed with Low-Temperature O2 Plasma

Author

Kawakami, Retsuo, Mimoto, Yuki, Yanagiya, Shin-ichiro, Shirai, Akihiro, Niibe, Masahito, Nakano, Yoshitaka, Mukai, Takashi, Kawakami, Retsuo, Mimoto, Yuki, Yanagiya, Shin-ichiro, Shirai, Akihiro, Niibe, Masahito, Nakano, Yoshitaka, and Mukai, Takashi

Abstract

Photodecomposition and photobactericidal activities of anatase/rutile-mixed phase TiO2 nanoparticles annealed with low-temperature O2 plasma were clarified by comparing them with those annealed in ambient air. The photocatalytic activities of plasma-assisted-annealed sample greatly enhanced as compared with the untreated sample, under not only ultraviolet irradiation but also visible-light irradiation. The photocatalytic activities of air-annealed samples did not enhance under ultraviolet irradiation but enhanced under visible-light irradiation. The enhanced photocatalytic activities due to the plasma-assisted annealing (PAA) originated from the increased photoexcited carrier concentration. This enhancement was discussed from PAA-induced characteristic factors. PAA facilitated the phase transformation to anatase, contributing directly to extending the photoexcited carrier lifetime. PAA introduced more oxygen vacancies, contributing to trapping more photogenerated electrons. PAA also introduced more bridging/terminal oxygen groups adsorbed on the surface, increasing the upward band-bending, the depletion layer width at the surface, and the charge transfer from rutile to anatase. These two introductions contributed to facilitating the separation of photoexcited carriers. Furthermore, PAA reduced the aggregate size of TiO2 nanoparticles formed on the surface, contributing to increasing optical absorptions. More reactive oxygen species produced from the bridging/terminal oxygen groups by the photoexcited carriers would also enhance the photocatalytic activities.

Published
2021

47. Wavefront measurement interferometry at the operational wavelength of extreme-ultraviolet lithography

Author

Zhu, Yucong, Sugisaki, Katsumi, Okada, Masashi, Otaki, Katsura, Liu, Zhiqiang, Kawakami, Jun, Ishii, Mikihiko, Saito, Jun, Murakami, Katsuhiko, Hasegawa, Masanobu, Ouchi, Chidane, Kato, Seima, Hasegawa, Takayuki, Suzuki, Akiyoshi, Yokota, Hideo, and Niibe, Masahito

Subjects
Interferometry -- Methods, Wavelength -- Measurement, Ultraviolet radiation -- Properties, Lithography, Electron beam -- Research, Astronomy, Physics
Abstract

Two basic types of interferometer, a point diffraction interferometer (PDI) and a lateral shearing interferometer (LSI) suitable for operation in the extreme-ultraviolet (EUV) wavelength region, are described. To address the challenges of wavefront measurement with an accuracy of 0.1 nm rms, we present a calibration method for the PDI that places a mask with two large windows at the image plane of the illumination point light source and a general approach to deriving the phase-shift algorithm series that eliminates the undesired zeroth-order effect in the LSI. These approaches to improving the measurement accuracy were experimentally verified by the wavefront measurements of a Schwarzschild-type EUV projection lens. OCIS codes: 120.3940, 120.5050, 120.3180, 120.2650, 260.7200, 220.3740.

Published
2007

48. Effects of nonequilibrium atmospheric-pressure O2 plasma-assisted annealing on anatase TiO2 nanoparticles

Author

Kawakami, Retsuo, Yoshitani, Yuki, Shirai, Akihiro, Yanagiya, Shin-ichiro, Koide, Hirofumi, Mimoto, Yuki, Kajikawa, Kosuke, Niibe, Masahito, Nakano, Yoshitaka, Azuma, Chisato, Mukai, Takashi, Kawakami, Retsuo, Yoshitani, Yuki, Shirai, Akihiro, Yanagiya, Shin-ichiro, Koide, Hirofumi, Mimoto, Yuki, Kajikawa, Kosuke, Niibe, Masahito, Nakano, Yoshitaka, Azuma, Chisato, and Mukai, Takashi

Abstract

Anatase TiO2 nanoparticles (NPs) immobilized on glass substrates were annealed with the assistance of nonequilibrium atmospheric-pressure O2 plasma. The plasma-assisted annealing greatly enhanced the photodecomposition and photobactericidal activity as compared with electric-furnace annealing. The plasma-assisted annealing reduced the TiO2 NP agglomerate size and increased the optical absorption, the photoinduced electrical conductivity, the amounts of bridging and terminal oxygen groups, and the (112)/(101) plane intensity ratio, causing the lattice oxygen deficiency that formed partially Ti-rich surface portions. The enhanced photobactericidal activity would arise from the bridging and terminal oxygen groups. The enhanced photodecomposition would arise from the increased concentration of photogenerated carriers due to the following three factors. The first is the optical absorption increased by the agglomerate size reduction and the (112) plane growth or appearance, which exert scattering more incident photons. The second is the charge separation of photogenerated carriers facilitated by the bridging and terminal oxygen groups, which originate from oxygen vacancies via oxygen ion impact from the plasma. The third is the charge transfer of plasmon-excited electrons from the partially Ti-rich portions to TiO2. The enhanced photodecomposition would also arise from more reactive oxygen species generated from the bridging and terminal oxygen groups by the photogenerated carriers.

Published
2020

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