OSCILLATORY BEHAVIOR IN THE SIZE DEPENDENCE OF CLUSTER MOBILITY ON METAL-SURFACES - RH ON RH(100)

The mobility of Rh clusters containing two to twelve atoms adsorbed on the Rh(100) plane is examined by field ion microscopy. The activation energy of surface diffusion exhibits an interesting, oscillatory behavior as a function of cluster size. Compact geometric structures (squares and rectangles) have a consistently higher activation energy than structures with extra atoms at the periphery. The atomic-level mechanism involved in cluster diffusion is inferred from a comparison of the measured activation energies to previous theoretical calculations.