Morphological Transitions in Solid Expitaxial Overlayers

We present a continuum model for the growth of solid epitaxial films which takes account of both surface tension and lattice mismatch. Layer-by-layer film growth is found to be unstable for fixed particle number. We show that the conventional nucleation and growth scenario for film decay is in error above the roughening temperature. Films decay to epitaxial solid “droplets” in coexistence with a microscopically thin, strained film through a barrierless mechanism which is closely related to spinodal decomposition. The decay of the film is triggered when the layer height exceeds the critical height beyond which misfit dislocations appear at the interface.