Low coverages of Co were deposited onto a Pt(111) surface, at room temperature, with vacancy islands providing a high density of steps. Scanning tunnelling microscopy, with chemical contrast, showed that the Co atoms did not descend Pt steps by diffusing over the step, but instead descended from the upper terrace to the lower one via an exchange diffusion process with Pt atoms at the step edge. The Co atoms did not descend a Pt step-edge via this process at straight A or B steps, but instead at the corners or kinks of the vacancy islands.

Interlayer Diffusion of Adatoms: a Scanning-Tunnelling Microscopy Study. E.Lundgren, B.Stanka, G.Leonardelli, M.Schmid, P.Varga: Physical Review Letters, 1999, 82[25], 5068-71