Single Atoms And Small Clusters In Fcc Metals (110) Surface Of Homoepitaxial Growth Process Upward Diffusion Mechanism

We study upward self-diffusion of adatoms and small clusters on facetted huts formed in fcc metal (110) homoepitaxy using molecular dynamics simulations with interatomic potentials described by the embedded-atom method (EAM). Our results show that both individual adatoms and small clusters on the (111)-sloped and (100)-sloped facets of the huts on Al and Cu(110) can readily diffuse upwards and cross the outer edges of the huts, but with different atomistic mechanisms. An adatom crosses the outer edges via a simple concerted exchange or indirect place exchange mechanism. In contrast, the upward diffusion and outer-edge crossing of small clusters is realized by their dissociation at or near the edges of the hut after one or two atoms belonging to the cluster are incorporated into the edges. The present simulation studies reveal that there truly exists efficient upward mass transport on facetted islands in fcc metal (110) homoepitaxy, and such upward diffusion processes are expected to play an important role in defining the kinetic faceting instability in these growth systems.