Long-period tetragonal lattice formation by solid-state alloying at the interfaces of Bi-Mn double-layer thin films

Thin Bi-Mn double-layer films, consisting of a Bi layer of 300 A in thickness and an Mn layer of 200 A prepared by successive vacuum deposition, were heated at 538 K for 100-200 h. Transmission electron micrographs show that a long-period tetragonal lattice forms at their interfaces, whose lattice constants were a=17.26, c=10.21 A. Near to the tetragonal lattice grains, structures preliminary to lattice formation were observed. Their electron diffraction and high-resolution micrographs show that the formation process can be divided into two stages. In the first stage, Bi and Mn atoms combine to form polyatomic clusters 16 A in diameter, which have a twelvefold symmetry axis normal to the (001) surface of the Bi crystals. In the second stage, these polyatomic clusters arrange themselves to build up the long-range tetragonal order. (orig.)