A new method for simulating the late stages of island coarsening in thin film growth: The role of island diffusion and evaporation

We have developed a method for simulating the evolution of an ensemble of o ne-atom-high islands from deposition and nucleation to coarsening. Using th is method we have studied three regimes of coarsening; coarsening due to is land coalescence, coarsening driven by evaporation, and the case in which b oth mechanisms act simultaneously. The parameters have been chosen to mimic coarsening of Ag on Ag(001); they are not meant to reproduce the experimen tal results for Ag quantitatively, but to provide simulations relevant to m etal-on-metal homoepitaxy. We find that the scaling laws proposed by the me an-field theory for the time dependence of the number of islands and the is land size distribution function work well in the limiting case when coarsen ing is dominated by island diffusion and coalescence. In the opposite limit , when coarsening is dominated by evaporation, the scaling predicted for th e island size works well, but the island size distribution predicted by the mean-field theory is narrower than the one found in simulations. In the ca se when island migration and evaporation are both important, the evolution of the number of islands shows a crossover; at early times it scales as if coarsening takes place by island coalescence, and at later times it scales as if coarsening is dominated by evaporation. Regardless of the coarsening mechanism, most islands disappear by coalescence. (C) 1999 American Institu te of Physics. [S0021-9606(99)01724-9].