Morphological stability of alloy thin films

We examine the linear stability of a planar, alloy thin film, growing by a deposition flux from the vapor. The stability of the film surface is influenced by stresses generated by both compositional inhomogeneity, via a composition dependent lattice parameter, and lattice mismatch between the film and substrate. The stress generated by the compositional inhomogeneities, which accompany nonplanar interfacial morphologies, can be either stabilizing or destabilizing. Under certain conditions, a growing planar film under tensile misfit-strain can be stable, whereas a growing film under the same magnitude of compressive strain can be unstable. These compositionally generated stresses can also lead to traveling or standing surface waves and unstable planar surfaces in lattice matched films. All of these instabilities can develop via the deposition process itself; the wave number dependence of the instability is different, however, from that in the pure surface diffusion limit. We also compare our results with numerous experimental observations.