Phase transitions in alloy clusters physically adsorbed on model surfaces

The lowest energy equilibrium structure for Ne-19, Ar-19, Ne-9 Ar-10, and N e12Ar7 clusters adsorbed on model surfaces was determined using simulated a nnealing techniques. In all cases, two-dimensional structures were obtained and in the case of the alloy clusters, a core structure was observed. Phas e transitions were identified by calculating anomalies in the constant volu me heat capacity as a function of temperature. In all cases, the usual melt ing and evaporation transitions were identified. In the case of alloy syste ms, various low temperature transitions were observed. These transitions ar e associated with order-disorder transitions which are similar to what is o bserved in alloy solids in bulk. The effect that surface corrugation has on these transitions was also analyzed. (C) 2000 American Institute of Physic s. [S0021-9606(00)51806-6].