STRESS-CORROSION AND STRESS-INDUCED SURFACE-MORPHOLOGY OF EPITAXIAL-FILMS

In addition to several new predictions, the general theory of thermody namic stability of heterogeneous systems with rearrangement has allowe d us to understand the roots of several experimental and theoretical r esults of the past. One of them is an outstanding paper of Asaro and T iller on stress corrosion cracking by surface diffusion published two decades ago. We compare results of Asaro and Tiller with conclusions o f thermodynamic theory of solids with rearrangement and develop some A saro-Tiller results in the directions dictated by the needs of thin fi lms technology and experiment. A surface diffusion model in a prestres sed elastic solid is studied on the basis of the Onsager approach of i rreversible thermodynamics. The master system governing a quasi-static evolution of the surface corrugations is derived in the framework of nonlinear elasticity and for the model of a surface energy incorporati ng both the Laplace excess pressure under curved interface and the Her ring curvature term in the local chemical potential. Then, we derive a dispersion relation of the growth rate of two-dimensional infinitesim al corrugations atop an isotropic uniformly stressed elastic layer cla mped to a substrate. The relation predicts different patterns of surfa ce morphology produced by the fastest unstable corrugations. The patte rning which develops depends on the applied stresses, thickness and ma terial parameters of the layer and substrate.