Equilibrium properties of binary and ternary metallic immiscible nanoclusters

Metropolis Monte Carlo free energy minimization in the (NPT) canonical ensemble is used to predict at the atomic scale the configurations of isolated metallic clusters made of two and three metals that are immiscible in the bulk. Clusters studied are formed by 200-1300 atoms by combining cobalt, silver, and copper. An embedded atom model potential is used to describe their cohesion. It is found that not only binding and interfacial configuration energies govern the composition of atomic configurations, but also thermal vibrational entropy plays a substantial role in the balance of energy contributions to thermodynamic equilibrium. Core-shell Ag-Co, Ag-Cu, and "onionlike" Cu-Co equilibrium configurations are found, which can be tuned by monitoring the interplay between composition and temperature. In ternary clusters, Ag always forms the surface layer and it is found that the Co and Cu distributions in the core depend on the Ag layer thickness.