Study of Electronic Structures near Lattice Defects in Metals by the Measuretment of Electron Momentum Distributions

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As compared with colour centers in ionic crystals and vacancy-oxygen complex in silicon crystals, the electronic structure of lattice defects in metals is not yet clear enough. However, recent developments in the measurement of two-dimensional angular correlation of annihilation radiations have allowed us to start precise and realistic investigations of electron momentum distributions and electron wavefunctions near lattice defects in metals and alloys. The purpose of the present project is to understand the electronic structure of lattice defects both in reciprocal space and in real space, by means of the two dimensional angular correlation machine and by their expansion. Results are summarized as follows;(1) The expansion of two-dimnsional angular correlation machin: we were successful in expanding the 128 detector system to the 256 detector systemby the use of specially designed electronic circuit. We raised the counting rate about four times.(2) The measurement of electron momentum … More distribution near thermal equilibrium defects in pure aluminum and aluminum based dilute alloys: We found that the Doppler broadening of annihilation radiations shows an abnormal narrowing near melting point in dilute alloys. This effect could not be observed by the measurement of positron lifetimes. In the 2D-ACAR experiment, the derived autocorrelation function is explained by the presence of vacancies in intermediate temperature range, but that near melting point corresponds to the presence of positroniums. From this fact, we proposed a nex positron trapping model.(3) The determination of Femi surface in oxide high temperature superconductors: In order to search the effect of oxygen deficiency, we did 2D-ACAR experiment. We cound not find any effect. From this fact, in turn, we can determine the Fermi surface. It was perfectly two-dimensional and one electron pillar and two kinds of hole pillars were found. (4) The direct observation of atomic excitons in lead based dilute alloys, and, (5) The measurement of electron momentum distribution around vacancies in electron irradiated nickel and the effect of hydrogens on it were performed. Less