Metastable evaporated thin films of CuAg and CoAu alloys-I occurrence and morphology of phases

Abstract

Metastable solid solutions of the CuAg and CoAu systems have been prepared by "vapor quenching" i.e. simultaneous vacuum evaporation of the two components onto a substrate held at liquid nitrogen temperature. The films so obtained are studied by resistivity measurements and by transmission electron microscopy and diffraction. The pure metals and dilute alloys are crystalline as deposited, while concentrated alloys (35-65% Ag for CuAg and 25-65% Au for CoAu) are amorphous when deposited on an amorphous substrate but crystalline when deposited onto a pure metal. The resistivity in the asdeposited state is almost independent of composition, but the annealing behavior of the various compositions is quite different. In particular, the high resistivity of the amorphous alloys anneals out in two distinct stages. In the first stage (near 370°K for CuAg and 430°K for CoAu) a transformation from amorphous to a metastable single-phase crystalline solid solution occurs in a narrow temperature range. The second stage, which is broader, involves the transformation to the equilibrium two-phase state. Structures at various stages of anneal are studied in detail by transmission microscopy and diffraction. A qualitative discussion is given of the reasons for the occurrence of the amorphous structure, for its relatively high metastability, and for its transformation first into a single-phase crystalline structure. © 1967.