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

The initial stages of nucleation of Ag on Si(111)-(7 x 7) surface - half un it 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 meas ured. The density of filled HUCs was found to be independent of the deposit ion 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 activate d diffusion of Ag adatoms between single HUCs starts to influence growth. A t lower temperatures, thermally activated hopping between HUCs is negligibl e. However, short-range correlations found in the structure of occupied HUC s 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 HU Cs plays an important role. (C) 2000 Elsevier Science B.V. All rights reser ved.