SPA-LEED STUDIES OF GROWTH OF AG ON AG(111) AT LOW-TEMPERATURES

The surface morphology after deposition of Ag on Ag(111) at low temperatures (130-200 K) has been studied in detail with SPA-LEED (Spot-Profile Analysis of Low-Energy Electron Diffraction). The surface roughness Delta and the mean terrace size Gamma have been quantitatively determined under various conditions. At 130 K the surface roughness Delta increases with coverage theta exactly according to the relation Delta = theta(1/2), which indicates that the inter-layer diffusion can be neglected at 130 K. Although the mean terrace length decreases with increasing coverage theta (following an approximate power law of Gamma proportional to Theta(-2/3)) for all studied coverages, it is much larger than expected for a pure random or Poisson-growth mode without any diffusion of the adatoms. Therefore, Ag grows on Ag(111) at this temperature without interlayer diffusion but with intra-layer diffusion. The intralayer diffusion barrier E(d) has been determined by measuring the temperature dependence of the two-dimensional island density according to the nucleation theory (supposing a critical nucleus size of one). The obtained value E(d) = 0.18 eV agrees with the theoretical calculations and previous measurements. Furthermore, from comparing measured and Monte-Carlo-simulated (MC) surface roughness Delta at different deposition temperatures we obtain Delta E = 0.05 eV as a lower limit for the additional barrier at steps.