EFFECT OF STRESS ON GRAIN-BOUNDARY MOTION IN THIN-FILMS

For thin films on a substrate, strains due to thermal expansion mismatch can produce very large stresses. While capillary forces create a grain boundary (GB) thermal groove, compressive and tensile stresses can form, respectively, a ridge or a canal at the grain boundary and can strongly influence the GB mobility. Following Mullins' analysis of the effect of thermal grooving on GB motion [Acta Metall. 6, 414 (1958)], this treatment shows that GB pinning is enhanced by the formation of the canal, whereas the formation of the ridge tends to repel grain boundaries. Analytical and numerical solutions for surface profiles of traveling grain boundaries under stress are presented. The results are discussed in the context of stress-induced grain growth and stress relaxation in thin films. The model also explains the formation of hillocks in thin films and offers the prospect of measuring GB self-diffusion coefficients and GB velocities. © 1995 American Institute of Physics.