Effect of surface anisotropy on the melting temperatures of free-standing gold nanofilms

A systematic study of the effect of surface anisotropy on the melting temperatures of free-standing gold nanofilms for various film thicknesses was carried out using molecular dynamics (MD) simulations. Caloric curves obtained from progressive heating of nanofilms showed sharp increase in energy at the transition temperatures due to the absorption of latent heat of melting. The importance of identifying the correct transition point (i.e., lower transition point) as the melting temperature was demonstrated. Melting temperatures of nanofilms were found to be lower than the bulk melting point. Significant decrease in the melting temperature with film thickness was observed for thicknesses below ∼6 nm. Among the films with low index crystallographic surfaces, those with {1 1 0} surface (least close-packed and highest surface energy) showed lowest melting temperatures whilst those with {1 1 1} surface (most close-packed and lowest surface energy) showed highest melting temperatures. Prolonged isothermal heat treatment demonstrated that there is no coexistence of equilibrium thickness of liquid layer with solid, in the case of free-standing nanofilm, below its melting temperature.