Site blocking in surface diffusion

Interactions between adatoms can change the diffusivity in a surface layer as the concentration is increased. Another effect that may contribute, howe ver, is sire blocking: the probability that an atom can find a sire into wh ich to jump diminishes as the concentration increases. The contribution of site blocking to the concentration dependence of the diffusivity is illustr ated by considering two non-interacting lattice gases: a Langmuir layer, an d a lattice gas with exclusion of nearest-neighbor sites. In both, site blo cking is shown to compete with the thermodynamic factor in affecting the di ffusivity. (C) 1999 Elsevier Science B.V. All rights reserved.