Diffusion and coalescence of bilayer surface-alloy islands of Pd(001)-p(2 x 2)-p4g-Al

We have studied thermally induced coarsening process in bilayer islands of ordered Al-Pd surface alloy on Pd(0 0 1). The island size distribution was deduced from scanning tunneling microscopy images recorded after annealing the surface at 500-700 K. Normalized size distribution function after annea ling at 500 K, at which temperature the bilayer surface alloy is formed, sh ows a sharp peak at u similar to 0.2, where u denotes the island size norma lized to the average size, with a long tail extending to u similar to 4. Up on annealing at higher temperatures, the peak shifts to larger it and gets broader. After annealing at 700 K, at which temperature the decomposition o f surface alloy sets in, the normalized distribution function resembles clo sely the universal scaling function predicted for coarsening due to diffusi on and coalescence of two-dimensional islands. The data is not consistent w ith the Ostwald ripening. (C) 2001 Elsevier Science B.V. All rights reserve d.