Enhanced solubility on surfaces: Molecular-dynamics simulations of an Ag overlayer on Cu(100)

Using molecular-dynamics simulations, we calculate the energetics of Ag deposited on Cu(100) surface and show that the driving force for substitutional surface alloying diminishes with increasing Ag coverage at 300 K. We further demonstrate that even at the Ag saturation coverage of close to one monolayer, the apparent positive enthalpy of mixing in surface layers is reduced relative to its value in the bulk and decreases with increasing temperature. As a result, intermixing between the reconstructed Ag overlayer and the underlying Cu surface layer can be observed at moderately elevated temperatures, forming a surface alloy well beyond equilibrium solid solubility limits.