SPA-LEED studies of growth of Ag on Ag(111) at low temperatures

Abstract

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 Δ and the mean terrace size Γ have been quantitatively determined under various conditions. At 130 K the surface roughness Δ increases with coverage θ exactly according to the relationΔ =θ ^1/2, which indicates that the inter-layer diffusion can be neglected at 130 K. Although the mean terrace length decreases with increasing coverage θ (following an approximate power law ofГ ℍΘ ^−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 barrierE _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 valueE _c=0.18 eV agrees with the theoretical calculations and previous measurements. Furthermore, from comparing measured and Monte-Carlo-simulated (MC) surface roughness Δ at different deposition temperatures we obtain ΔE=0.05 eV as a lower limit for the additional barrier at steps.