Size-Selective Dynamics of Large Hetero-Epitaxial Islands on FCC(001) Surfaces

In this work, we use molecular dynamics simulations to investigate the diffusion of hexagonal silver monolayer islands on copper and nickel substrates. Our results indicate that certain sized islands diffuse orders of magnitude faster than other sized islands and even single atoms under similar conditions. An analysis of several low-energy pathways reveals two governing processes: a rapid, glide-centric process and a slower, vacancy-assisted one. We believe that the relative magnitude of the vacancy formation energies plays a role in determining the size-selective diffusion of these islands. These findings should provide insight to future experimental research on the size distribution and shapes observed during the growth of thin films in similar systems. Furthermore, our results should have implications for Monte Carlo models of film growth which generally allow only single atom diffusion, thus neglecting such complex, cooperative mechanisms.