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 Ne12Ar7 clusters adsorbed on model surfaces was determined using simulated annealing techniques. In all cases, two-dimensional structures were obtained and in the case of the alloy clusters, a core structure was observed. Phase transitions were identified by calculating anomalies in the constant volume heat capacity as a function of temperature. In all cases, the usual melting and evaporation transitions were identified. In the case of alloy systems, various low temperature transitions were observed. These transitions are associated with order-disorder transitions which are similar to what is observed in alloy solids in bulk. The effect that surface corrugation has on these transitions was also analyzed. (C) 2000 American Institute of Physics. [S0021-9606(00)51806-6].