Step decoration and surface alloying: growth of cobalt on Ag(100) as a function of deposition temperature

The temperature dependence of the growth of cobalt on Ag(100) has been stud ied with scanning tunneling microscopy. For submonolayer coverage, the pref erred sites of nucleation change with increasing temperature from a random distribution over the terraces to decoration of the silver steps on the upp er side. Because of the step decoration, the silver surface, which has prop agating steps at elevated temperatures, is frozen into a stable configurati on. Numerical analysis of island densities gives an estimation of 0.6(2) eV for the diffusion barrier for cobalt on Ag(100). Higher deposition tempera tures result in the formation of a surface alloy. For higher coverages, how ever, high-temperature deposition or post-annealing after room-temperature deposition does not lead to a cobalt film completely covering the silver su rface, but to the formation of clusters embedded in irregular-shaped silver terraces. An explanation is given in terms of a competition between the su rface for energy and the heat of mixing. (C) 2000 Elsevier Science B.V. All rights reserved.