It was found that a Re-Ir dimer-vacancy complex could be formed on an (001) Ir surface when the latter was heated to about 240K under a surface Re atmosphere. At temperatures above about 210K, the geometrical center of this complex could be displaced by 1 step of the substrate by exchange displacement of its Ir atom with a substrate Ir atom. The mechanism limited the movement of the complex to 4 nearest-neighbor sites of the substrate lattice. Only at temperatures above about 235K could the complex move out of the 4 sites via a combined hopping-exchange mechanism. At temperatures above about 280K, the Re-Ir dimer could dissociate. Upon dissociation, the Re atom combined with the vacancy, and self-diffusion of Ir then occurred.

C.Chen, T.T.Tsong: Physical Review Letters, 1994, 72[4], 498-501