STM study of nucleation of Ag on Si(111)-(7×7) at submonolayer coverage

The initial stages of nucleation of Ag on Si(111)-(7×7) surface – half unit cell (HUC) filling – were studied in situ by UHV STM. The dependence of the density of Ag-occupied HUCs and of the preference in occupying HUCs on substrate temperature, deposition rate and amount of Ag deposited were measured. The density of filled HUCs was found to be independent of the deposition rate at room temperature. The density is independent of temperature up to 380 K (for a deposition rate of 0.0075 ML s−1) when thermally activated diffusion of Ag adatoms between single HUCs starts to influence growth. At lower temperatures, thermally activated hopping between HUCs is negligible. However, short-range correlations found in the structure of occupied HUCs together with the low density of occupied HUCs at coverage 0.1 ML at room temperature show that non-activated adatom capture by adjacent occupied HUCs plays an important role.