Papers by Author: Masaki Sakurai

Abstract: The atomistic structure of Czochralski-grown SixGe1-x binary mixed semiconductor was studied experimentally and theoretically. By extended X-ray absorption fine structure (XAFS) studies it was found that bulk SiGe semiconductor is a random mixture and that the Ge-Ge, Ge-Si and Si-Si bond lengths maintain distinctly different lengths and vary in a linear fashion against the alloy composition across the whole composition range 0 < x < 1, in good agreement with expectations derived from the ab-inito electronic structure calculations. The result indicates that SiGe is a suitable model for a disorder mixed material and that the bond lengths and bond angles are distorted with the composition.

Abstract: XAFS measurements of the Cu, Ni and Zr K-edges for the melt-quenched Zr67Cu33 and Zr67Ni33 metallic glasses were curried out using synchrotron radiation at 20K. Fitting calculations for the EXAFS results reveal that local structure around Ni and Zr in Zr67Ni33 is well represented by those for the crystalline Zr2Ni, while local structure around Zr in Zr67Cu33 is better fitted by an icosahedron rather than crystalline Zr2Cu. Such differences of the local structure attribute to the differences of the stability of super-cooled liquid state and glass formability between Zr67Cu33 and Zr67Ni33 metallic glasses.

Abstract: The purpose of this research is to investigate the micro-mechanism of anelastic behavior of metallic glass. The changes of atomic arrangement in Cu50Zr50 metallic glass were observed directly by EXAFS method during tensile deformation. The transmission-mode EXAFS measurements around Zr K-edge and Cu K-edge of the sample in various amounts of tensile deformation conditions were done. The interatomic distance between Cu-Zr increased, and that between Zr-Zr decreased simultaneously, with the amount of tensile deformation increase of the sample at first stage of deformation. When the atomic distances reached to certain values respectively, they recovered to the initial values of no tensile deformation condition at first stage, and then the atomic distances changed as same manner as the first stage of deformation, respectively. This is the first observation on the change of atomic arrangement during tensile deformation of metallic glass.

Abstract: Near-edge structure of X-ray absorption spectrum (NEXAFS) of various Ti-oxides were investigated by combined with first principles orthogonalized linear combinations of atomic orbitals (OLCAO) method. From experimental and theoretical studies on the NEXAFS of the tetravalent and trivalent Ti-oxides, including rutile, anatase, brookite, columbite, and Ti2O3, it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main-peak of Ti-K NEXAFS.