Diffusion on aluminum-cluster surfaces and the cluster growth

Diffusion of adatoms have been studied on fcc polyhedral aluminum-cluster surfaces by molecular-dynamics simulations using the effective-medium theory. Diffusion of adatoms has been shown to take place by hopping along {111} facets at very low temperatures. Diffusion from one {111} facet to other {111} facets takes place at higher temperatures through a variety of mechanisms, and finally diffusion to and along {100} facets takes place at high temperatures. Diffusion from {100} to {111} facets is possible only close to the melting temperature of the cluster. The appearance of different diffusion processes as a function of temperature is in good agreement with the calculated activation energies of diffusion mechanisms along different facets and from one facet to another, including different hopping and exchange processes as well as more exotic events like the chain mechanism through a {100} facet between two {111} facets. Observed diffusion mechanisms imply that fcc clusters can grow epitaxially, having only {111} facets in accord with experimental observation. Our dynamical simulations of cluster growth support these findings.