  The dynamics of desorption from a submonolayer of adsorbed atoms or ions are
significantly influenced by the absence or presence of lateral diffusion of the
adsorbed particles. When diffusion is present, the adsorbate configuration is
simultaneously changed by two distinct processes, proceeding in parallel:
adsorption/desorption, which changes the total adsorbate coverage, and lateral
diffusion, which is coverage conserving. Inspired by experimental results, we
here study the effects of these competing processes by kinetic Monte Carlo
simulations of a simple lattice-gas model. In order to untangle the various
effects, we perform large-scale simulations, in which we monitor coverage,
correlation length, and cluster-size distributions, as well as the behavior of
representative individual clusters, during desorption. For each initial
adsorbate configuration, we perform multiple, independent simulations, without
and with diffusion, respectively. We find that, compared to desorption without
diffusion, the coverage-conserving diffusion process produces two competing
effects: a retardation of the desorption rate, which is associated with a
coarsening of the adsorbate configuration, and an acceleration due to
desorption of monomers "evaporated" from the cluster perimeters. The balance
between these two effects is governed by the structure of the adsorbate layer
at the beginning of the desorption process. Deceleration and coarsening are
predominant for configurations dominated by monomers and small clusters, while
acceleration is predominant for configurations dominated by large clusters.
