Long-time scale molecular dynamics study of diffusion dynamics of small Cu clusters on Cu(111) surface

Diffusion dynamics of small two-dimensional atomic clusters Cu-n (with n ranging from 1 to 8) on Cu(111) surface have been studied using molecular dynamics in the temperature range from 300 to 800 K. The diffusion coefficients of these clusters are derived from mean square displacement of cluster's mass-center, which is obtained by long simulation times (similar to 0.1 mu s) and tracing of surface interstitial atoms. A drop in the diffusion migration energy for tetramer compared to the trimer or pentamer is found, and the migration energy for octamer is larger than that for the compact heptamer cluster. The diffusion prefactor of a heptamer is about 30 times larger than that for single atom diffusion. The characteristic temperature, derived from the Arrhenius plots, indicates that the heptamer starts to move at very low temperature (167 K).