Reentrant morphological instability of epitaxial islands

The morphological stability of two-dimensional islands nucleated on a square-symmetry substrate during vacuum atom deposition is investigated by analytic scaling arguments and kinetic Monte Carlo simulations. It is shown that nonequilibrium, dendritic-skeletal island shapes may be converted into compact, equilibrium ones by increasing the deposition rate, in contrast with simple expectation. Our results imply that epitaxial islands generically should undergo a reentrant morphological transition with varying deposition rate. Stable, compact shapes should in principle exist only at intermediate values of the deposition rate.