ATOM MOVEMENT AND BINDING ON SURFACE CLUSTERS - PT ON PT(111) CLUSTERS

Binding and diffusion of single platinum atoms adsorbed on platinum cl usters on Pt(111) have been explored using helium-cooled field ion mic roscopy. Pt atoms deposited on Pt(111) clusters at T similar to 20 K a re found at both fcc and hcp sites. At hcp sites, atoms are more weakl y bound; after annealing at temperatures as low as 45 K, they occupy f cc sites exclusively. The cluster surface itself is not uniform, howev er. An empty zone separates the central region from the cluster edges: Atoms in the center have to overcome an energy barrier just to cross this empty zone and reach the cluster edges.