The adsorption sites of isolated 111In and 111mCd atoms which were evaporated onto (111) Pd surfaces, and their diffusion behavior, were investigated as a function of temperature. By using the perturbed γ-γ angular correlation technique, various absorption sites could be characterized in terms of the hyperfine interaction of the electric field gradient with the nuclear quadrupole moment of the radioactive probe nuclei. It was found that 5 adsorption sites were successively occupied by the adatoms during annealing at temperatures of between 80 and 600K. The first site was attributed to In atoms, which occupied terrace sites on top of the first Pd layer; already moving to step sites at temperatures below 120K. On vicinal (111) Pd surfaces, In and Cd atoms behaved in a very similar manner; successively occupying step sites, kink sites and substitutional step sites during isochronal annealing. At temperatures above 380K, both probe atoms took up substitutional terrace sites and replaced a Pd atom in the first layer. From the conversion temperature between various sites, approximate values for the activation energies could be estimated. The data were consistently explained by an activation energy of 0.76eV for Pd surface self-diffusion.

E.Hunger, H.Haas: Surface Science, 1990, 234[3], 273-86