Continuous Phase Transitions at Surfaces of CuAu Alloy Models — A Monte Carlo Study of Surface Induced Order and Disorder

Abstract

The influence of surface on phase transitions has found significant attention in recent years, and a number of excellent reviews exists. [1, 2, 3] A variety of complex phenomena occur which are also related to the physics of adsorption and wetting. The scenario of wetting requires three distinct phases, for instance the vacuum, the bulk phase and a third phase intervening in between at equilibrium. In case of surface induced disorder (SID, a film of disordered layers at the surface “wets” the bulk phase as the temperature approaches the bulk transition temperature T c,b. The transition at the surface may be continuous (standard critical wetting phenomena), and, as theoretically investigated in detail by Lipowsky[3], it may remain to be continuous even in the case of a discontinuous bulk transition. It may appear natural that missing bonds at a surface induce more disorder near the surface, as it is also observed for the equivalent phenomena of surface induced melting, e. g. for metals like lead and aluminum. [4] In the present study of a CuAu alloy model (using only nearest neighbor interactions) SID is for instance found for a CuAu alloy model (using only nearest neighbor interactions) SID is for instance found for a (111) surface, but it will certainly occur at some other facets as well. This particular case serves to test the actual theories of wetting. However, SID is not necessarily what occurs and instead surface induced order (SIO) can be observed in our model for instance at a (100) surface.