The order-disorder transformation at a (100) surface of Cu 3Au : Theory and experiment

Abstract

The temperature dependence of long range order at a (100) surface of Cu 3Au has been determined by low energy electron diffraction. Auger electron spectroscopy revealed that the composition of the alloy near the surface is changed by ion bombardment, but the stoichiometric composition is reconstituted by annealing. The order parameter of the surface, which was obtained from the temperature dependence of a superlattice beam, appears to be a continuous function of temperature, unlike the bulk order parameter. The disordering process at the surface begins about 60°K below a critical temperature which is common to both the surface and the volume. Monte Carlo calculations of the order parameter as a function of temperature for a model incorporating nearest- and next-nearest-neighbor interactions reproduce the experimental results and also provide an evaluation of the change in order parameter as a function of layer number for boundary conditions corresponding to a copper or a copper-gold surface.