Existence of shallow facets at the base of strained epitaxial islands

We generalize a previous analysis of equilibrium shapes of strained epitaxial islands, to include the possibility of facets of smaller slope both above and below facets of greater slope. We find that the lower shallow facet exists exactly when the upper shallow facet does. Thus the conclusions of our previous analysis are unaffected, except that the actual island shape is modified by the presence of an additional facet in certain cases.