DIFFUSION BEHAVIOR OF PT ADATOMS AND CLUSTERS ON THE RH(100) SURFACE

The diffusion of individual Pt adatoms and clusters of two to six Pt atoms on the (100) surface of Rh has been investigated by field ion microscopy. The diffusion mode for adatoms and clusters is determined to be conventional site-to-site hopping. Single adatoms and dimers migrate in the temperature range from 314 to 346 K with an activation energy of 0.92 eV. Trimers and tetramers, which are more stable as one-dimensional chains than two-dimensional islands, as well as pentamers, which are equally stable as chains and islands, all diffuse with the same activation energy of 1.03 eV. Hexamers, which are more stable as islands than chains, migrate with a somewhat higher activation energy of 1.16 eV. The relative stabilities of the chain versus island configurations indicate the presence of long-range adatom-adatom interactions in the clusters. The implications of the unexpected activation barriers for cluster diffusion are discussed.