| Research Abstract |
In order to accelerate experiments more effectively, a high-vacuum-deposition apparatus equipped with an electron-beam-evaporator with a large capability was designed and constructed. It has been successfully used, since 1990, for preparing composite double layer thick films consisting of a Bi layer 5000 A and of a Mn layer 2000 A in thickness.
By co-deposition of Bi and Mn, it was found that non-crystalline alloy films are obtained when their composition is between 65 and 85 at% Mn. When warmed up at 180^ﾟC, crystallization of the "nucleation and grain growth" type takes place and obtained crystals have a new metastable hexagonal lattice of a = 19.97 A, c = 4.49 A. Atomic arrangement within this large lattice was determined from its electron diffraction patterns, high resolution electron micrographs and their computer simulation. In composite double layer Mn-Bi films prepared by successive deposition, as many as more than four kinds of new alloy phases were obtained by solid-state alloying due to low temperature heating below the melting point of Bi, although only one phase, ferromagnetic MnBi, is described to exist in the equilibrium phase diagram. They include a long-period tetragonal phase with a = 17.26 A, c = 10.21 A, and a quasicrystal having twelve-fold symmetry, which will have intimate structural relation to the long-period tetragonal phase.
Structure analysis of the metastable hexagonal phase is one of a few examples of performing the analysis only by electron microscopy. The quasicrystal with twelve-fold symmetry is the one first observed in the world and is now in press in Philosophical Magazine Letters. Atomic arrangement of the long-period tetragonal phase is being looked for referring to the sigma-phase structure and so on. Deposition experiment of Fe-Zn system was just started in an aim of making some contribution to industrial manufacturing of galvanized steel sheets.
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