Field ion microscopy was used to study surface atomic processes when an adatom differed chemically from surface atoms. It was noted that, on the (001) surface, an adsorbed Re atom displaced an Ir atom from the substrate to form a Re-Ir vacancy-bound complex at about 230K. Upon heating samples to about 300K, this complex dissociated and the Re atom was incorporated into the surface. The Re-Ir clusters could also be removed by field evaporation so as to leave a lattice vacancy, into which another adatom could then diffuse.

T.T.Tsong, C.Chen: Nature, 1992, 355, 328-31