Influence of the electrochemical potential on energy landscapes near step-and island-edges: Ag(100) and Ag(111)

The electrochemical cell offers the promise of enabling controlled alterati on of the morphology and islanding phenomena on metallic surfaces. Differen t diffusion processes near step and island edges are known to profoundly af fect the growth mode, island sizes, island shapes and step morphology. Usin g the surface-embedded-atom model (SEAM) modified for the electrolytic envi ronment, we calculate the dependence of the activation energies for these d iffusion processes on the electrochemical potential for the Ag(100) and Ag( 111) surfaces. While all these processes show some degree of dependence on the potential, the step-edge barrier and the edge diffusion processes are t he most sensitive. Step-edge barriers for Ag(111) increase (to over 1 eV) w ith a 1.0 V potential (relative to the potential of zero charge (PZC)). The variations for Ag( 100) are not as large (about 0.3 eV), but the excess st ep-edge barrier can be negative for high positive (> +0.6 V) or negative (< -0.4 V) potentials owing to the competing roles of hopping and exchange di ffusion processes and their dependencies on the potential. Edge diffusion d ecreases rapidly with potential for both (100) and (111) surfaces. Signific ant variations are also found for diffusion around corners and kinks, which play important roles in island morphology. We assess the influence these v ariations have on island sizes, shapes, diffusion, and coarsening. From thi s discussion, we show how the electrochemical potential can he used to cont rol the fractal or compact nature of islands, and the magnitude and scaling exponent for island diffusion and coarsening. (C) 2001 Elsevier Science B. V. All rights reserved.