Effect of atomic diagonal motion on cluster diffusion coefficient and its scaling behavior

The effect of atomic diagonal motion on the cluster diffusion and its size dependence is simulated by kinetic Monte Carlo method. The diffusion coefficient D(N) of a cluster with size N satisfies a power law D(N)∝N−α, where the scaling exponent α decreases with the increase of additive diagonal motion barrier Ed. When Ed is very small, the cluster diffusion is dominantly controlled by periphery diffusion mechanism and α is found to be about 1.5. On the contrary, when Ed is very large, the cluster diffusion is mainly controlled by the correlation evaporation and condensation (CEC) mechanism and α approaches 1.0. Furthermore, a threshold Edt∼0.4E0 (E0 is the diffusion barrier for a free adatom), corresponding to the transition of different dominant mechanisms for the cluster diffusion, is found existing in the relationship between D and Ed. When Ed<Edt, the cluster diffusion is mainly controlled by the diagonal motion of the atom, and D decreases drastically with increasing Ed. When Ed>Edt, the CEC mechanism is more important, and D is nearly independent of Ed. Additionally, the temperature dependent of D is found to be D∼exp(−EakBT) and the active energy Ea is found to ∼1.42E0.