MORPHOLOGICAL STABILITY OF ALLOY THIN-FILMS

We examine the linear stability of a planar, alloy thin film, growing by a deposition Aux from the vapor. The stability of the film surface is influenced by stresses generated by both compositional inhomogeneit y, via a composition dependent lattice parameter, and lattice mismatch between the film and substrate. The stress generated by the compositi onal inhomogeneities, which accompany nonplanar interfacial morphologi es, can be either stabilizing or destabilizing. Under certain conditio ns, a growing planar film under tensile misfit-strain can be stable, w hereas a growing film under the same magnitude of compressive strain c an be unstable. These compositionally generated stresses can also lead to traveling or standing surface waves and unstable planar surfaces i n lattice matched films. All of these instabilities can develop via th e deposition process itself; the wave number dependence of the instabi lity is different, however, from that in the pure surface diffusion li mit. We also compare our results with numerous experimental observatio ns.