Experimentally, there was a critical thickness of an epitaxial thin film, below which misfit dislocations were not observed and above which threading dislocations were found to glide. There were several theoretical critical thicknesses that may or may not coincide with the observed value. It was shown that the presence of a properly aligned surface step could strongly influence the motion of a threading dislocation, enhancing or retarding its motion. Anisotropic elastic and elastic inhomogeneity effects were considered. The results were discussed in terms of the critical thickness concept. The anisotropic elastic prediction of the critical thickness for spreading agrees well with the experimental results for a Ni film on Cu.

The Effect of Surface Steps on the Critical Thickness for Spreading of Threading Dislocations in Thin Epitaxial Films. J.P.Hirth, R.G.Hoagland, A.Misra: Philosophical Magazine, 2005, 85[26-27], 3019-28