From erosion to bombardment-induced growth on Ir(111)

The morphology of the ion bombarded Ir(111) surface is studied using scanning tunneling microscopy. At a temperature of 880 K and ion fluences of the order of 10(17) ions/m(2) the experiments show a transition from an erosion regime to a bombardment-induced growth regime with increasing ion energy at energies of a few keV. In dependence of ion fluence, for energies exceeding a few keV a transition from bombardment-induced growth to erosion is observed. The growth effect is caused by the bombardment-induced formation of bulk vacancy clusters, remaining at the bombardment temperature still stable against diffusion and annealing at the surface. Annealing experiments show a gradual decrease of bombardment-induced subsurface damage with increasing temperature. Ion energy, ion fluence, and temperature dependence of the growth phenomenon are explained in terms of an effective damage area below the surface.