Masaaki Hirai
Okayama University
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Featured researches published by Masaaki Hirai.
Surface Science | 1997
T. Tsukamoto; Masaaki Hirai; Masahiko Kusaka; Motohiro Iwami; T. Ozawa; T. Nagamura; T. Nakata
Abstract We have investigated heat-treated 4H- and 6H-SiC(001)Si surfaces using AES, LEED, EELS and STM in ultra high vacuum (UHV). √3 × √3 and 6 × 6 reconstructions were observed in the STM study at ∼1000 and ∼1200°C, respectively. On the other hand, 6√3 × 6√3 superstructure was observed by LEED at ∼1200°C. The AES p-p height ratio of Si ( LVV ) C ( KLL ) decreased at higher temperatures. EELS proved the existence of a graphite layer on top of the specimen surface. Considering these experimental results, the 6 × 6 reconstruction observed by STM can be explained as a moire pattern produced by a graphite layer sitting on top of the SiC surface.
Applied Surface Science | 1997
Jinliang Wang; Masaaki Hirai; Masahiko Kusaka; Motohiro Iwami
Abstract A thin film formation of MnSi and MnSi 1.7 on a silicon substrate through solid phase reaction has been studied, where MnSi 1.7 is one of the few semiconducting silicides, while MnSi is a metallic one. The growth process and electronic states of manganese silicides with composition of MnSi and MnSi 1.7 are investigated by several methods, including soft X-ray emission spectroscopy.
Japanese Journal of Applied Physics | 1990
Motohiro Iwami; Masaaki Hirai; Masahiko Kusaka; Masaru Kubota; Sekika Yamamoto; Hatsuo Nakamura; Hirokuni Watabe; Masao Kawai; Hiroyoshi Soezima
A soft X-ray emission spectroscopy (SXES) apparatus was constructed using a grating monochromator. The resolution was sufficient to show differences in valence electronic structures of Si compounds including pure Si crystal. A nondestructive analysis of a Ni/Si(111) specimen with heat treatment was carried out using either a clear difference in Si L2,3 SXES spectra of Ni silicide and Si single crystals or the fact that the soft X-ray production depth increases in a solid with increasing energy of a primary electron, Ep. The electronic and atomic structures of the surface and interface of specimens adopted were clarified with Ep varying between 1.5 and 10 keV.
Journal of the Physical Society of Japan | 2009
Rikiya Yoshida; Takanori Wakita; Hiroyuki Okazaki; Yoshikazu Mizuguchi; Shunsuke Tsuda; Yoshihiko Takano; Hiroyuki Takeya; Kazuto Hirata; Takayuki Muro; Mario Okawa; K. Ishizaka; Shik Shin; Hisatomo Harima; Masaaki Hirai; Yuji Muraoka; Takayoshi Yokoya
We have performed soft x-ray and ultrahigh-resolution laser-excited photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to band structure calculations and yields a reasonable assignment of partial densities of states. However, the sharp peak near the Fermi level slightly deviates from the calculated energy position, giving rise to the necessity of self-energy correction. We have also performed ultrahigh-resolution laser photoemission experiment on FeSe and observed the suppression of intensity around the Fermi level upon cooling.
Physical Review B | 2010
Hiroyuki Okazaki; T. Wakita; T. Muro; Y. Kaji; X. Lee; H. Mitamura; N. Kawasaki; Y. Kubozono; Y. Yamanari; T. Kambe; Takashi Kato; Masaaki Hirai; Yuji Muraoka; Takayoshi Yokoya
We use photoemission spectroscopy to study electronic structures of pristine and K-doped solid picene. The valence band spectrum of pristine picene consists of three main features with no state at the Fermi level (E F ) while that of K-doped picene has three structures similar to those of pristine picene with new states near E F , consistent with the semiconductor-metal transition. The K-induced change cannot be explained with a simple rigid-band model of pristine picene but can be interpreted by molecular-orbital calculations considering electron-intramolecular-vibration interaction. Excellent agreement of the K-doped spectrum with the calculations points to importance of electron-intramolecular-vibration interaction in K-doped picene.
Surface Science | 1988
Motohiro Iwami; Masahiko Kusaka; Masaaki Hirai; Hatsuo Nakamura; K. Shibahara; Hiroyuki Matsunami
Abstract Valence band, Si L2.3 and C K, soft X-ray spectroscopy (SXS) by the electron excitation method has been applied for the first time to a non-destructive analysis of hetero-interfaces, i.e. Si(100) surfaces with an ultra-thin-film on top, and the valence band spectra show a clear change from that of pure SiC to that of pure Si with the primary electron energy, Ep, from 0.85 to 4 keV. The present work explores the usefulness of this new application of the SXS method by studying experimentally the carbonized-layer (ultra-thin-film)/Si(100) system and the following results were obtained: the carbonized-layer is found to be a thin SiC layer which grows uniformly on the Si(100) surface, the SiC/Si(100) interface shows a rather sharp transition to the Si substrate and the thickness of the SiC layer is estimated to be ≲ 20 nm with possible undulation.
Applied Surface Science | 1997
T. Tsukamoto; Masaaki Hirai; Masahiko Kusaka; Motohiro Iwami; Takehiro Ozawa; Toshihiko Nagamura; T. Nakata
Abstract We have investigated 4H- and 6HSiC(0001)Si faces prepared by heat treatment using Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) in ultra high vacuum (UHV). The following were elucidated: 3 × 3 reconstruction was observed on the surface prepared at ∼ 1000°C, while 6 × 6 superstructure was observed for a specimen prepared at ∼ 1200°C. The 6 × 6 reconstruction can be explained as a moire pattern produced by a graphite layer sitting on top of SiC surface. Also AES p-p height ration of Si(LVV) C(KLL) decreased at a higher temperature for 4HSiC than for 6HSiC, which could be due to the fact that the bond strength of 4HSiC is more than that of 6HSiC.
Japanese Journal of Applied Physics | 1995
Yoshitomo Marumoto; Takeshi Tsukamoto; Masaaki Hirai; Masahiko Kusaka; Motohiro Iwami; Takehiro Ozawa; Toshihiko Nagamura; Toshitake Nakata
A scanning tunneling microscopy in ultrahigh vacuum (UHV) has been used to study hexagonal (6H) silicon carbide (0001)Si face prepared by heat treatment. √3 x √3, 6 x 6 and 3 x 3 reconstructions were observed above 1100°C. With increasing heat-treatment temperature, surface structure changed drastically and step heights decreased to that of a double layer. The 6 x 6 and 3 x 3 reconstructions can be explained as the structure of a graphite layer on the SiC surface and as the structure proposed by Kaplan, respectively.
Thin Solid Films | 1996
Claire Heck; Masahiko Kusaka; Masaaki Hirai; Motohiro Iwami; Yasuhiro Yokota
Abstract CrSi2 is grown on Si(001) substrate with solid-phase reaction. Samples are prepared by one-step annealing and their structure is analyzed with transmission electron microscopy. A new epitaxial growth relation is found, that is, CrSi2(001)//Si(001) with CrSi2(110)//Si(110).
Japanese Journal of Applied Physics | 1992
S. Yamauchi; Masaaki Hirai; Masahiko Kusaka; Motohiro Iwami; Hatsuo Nakamura; Shigeru Minomura; Hirokuni Watabe; Masao Kawai; Hiroyoshi Soezima
We constructed a sample reclining stage for soft X-ray emission spectroscopy (SXES), where we intended to carry out nondestructive depth profiling using an incident angle variation (IAV) method. The penetration depth of an incident electron decreases with a reclining sample stage. One of the characteristics of the IAV method is that the incident electron beam energy is constant; thus, it is easy to obtain information related to a quantitative analysis of the integrated intensity of soft X-ray emission spectra. This method has been applied for a specimen with NiSi2/Si(111) structure. We have analyzed the change in shape of the Si L2,3 emission band spectrum in a region of the Si substrate to the NiSi2 layer, and have shown that we can determine the distribution of the Si element from the integrated intensity of Si L2,3 emission spectra.