Iso-coverage diffusion zones observed with LEEM during annealing of Ag on Si(001)*

During high temperature annealing of 3D Ag islands grown on Si(001) PEEM images reveal the emergence of a bright zone surrounding the decaying islands. Microdiffraction patterns from these bright areas display a (2x3) Ag reconstruction. The decaying Ag islands act as sources of Ag adatoms which then diffuse on the surface. The (2x3) reconstruction spreads away from the island to a distance determined by the interplay of diffusion and desorption, and by the local coverage of Ag: the outer boundary of the imaged diffusion zones constitutes an ``iso-coverage boundary.'' We describe the time and temperature behavior of these iso-coverage zones, and present a simple continuum model that describes the iso-zone size as a function of the diffusion and desorption rates.