Diffusion of small 2-dimensional Cu islands (containing up to 10 atoms) on Cu(111) was studied using the newly developed self-learning kinetic Monte Carlo method which was based upon a database of diffusion processes and their energetics accumulated automatically during the implementation of the self-learning kinetic Monte Carlo code. Results obtained from simulations in which atoms hop from one face-centered cubic hollow site to another were compared with those obtained from a parallel set of simulations in which the database was supplemented by processes revealed in complementary molecular dynamics simulations at 500K. They included processes involving the hexagonal close-packed (stacking-fault) sites, which facilitate concerted motion of the islands (simultaneous motion of all atoms in the island). A significant difference in the scaling of the effective diffusion barriers with island size was observed in the two cases. In particular, the presence of concerted island motion led to an almost linear increase in the effective diffusion barrier with size, while its absence accounted for strong size-dependent oscillations and anomalous behavior for trimers and heptamers. The key microscopic processes responsible for diffusion were identified and the frequencies of their occurrence were examined as a function of island size and substrate temperature.

Diffusion of Small Two-Dimensional Cu Islands on Cu(111) Studied with a Kinetic Monte Carlo Method. A.Karim, A.N.Al-Rawi, A.Kara, T.S.Rahman, O.Trushin, T.Ala-Nissila: Physical Review B, 2006, 73[16], 165411 (11pp)