Comparative study of compact hexagonal cluster self-diffusion on Cu(1 1 1) and Pt(1 1 1)

Self-diffusion behaviors of two-dimensional compact hexagonal Cu7 and Pt7 clusters on (1 1 1) surface are studied with molecular dynamics simulation. The diffusion barriers (Em) and prefactors (D0) are determined from the Arrhenius diagram and compared with recent low-temperature field ion microscopy experiment. We find that D0 of Pt7 cluster is about 35 times larger than that of Cu7 cluster. From the calculated phonon spectral densities of adatoms, we suggest that the different diffusion behaviors of the two clusters may result from strong interactions between the Pt adatoms and surface atoms, which make the nonequivalent self-diffusion processes, which can produce a high prefactor, occur more easily for Pt7 cluster.