Theory of adsorption and surfactant effect of Sb on Ag(111)

We present first-principles studies of the adsorption of Sb and Ag on clean and Sb-covered Ag(111). For Sb, the substitutional adsorption site is found to be greatly favored with respect to onsurface fcc sites and to subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag. We propose that the experimentally reported surfactant effect of Sb is due to Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high density of Ag islands which coalesce into regular layers.