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Published online by Cambridge University Press: 10 February 2011
This paper discusses variants that occur in heteroepitaxy when the substrate possesses symmetries that are absent from the epilayer. Variants are enumerated in terms of 2-D symmetries of the substrate and epilayer, as they exist terminated at their interface. In this formulation, all possible cases can be presented in a single table. The role of miscut in controlling otherwise equal variants proportions is discussed with a view to eliminating unwanted variants and thereby improving the translational invariance of the materials. We summarize an experimental study of a (3m) symmetry epilayer growing on a (2mm) substrate, specifically Cu3Au (111) grown by molecular beam epitaxy on Nb (110), for which the two variants predicted from symmetry are stacking twins. Miscuts of about 1° along the indicated azimuth are sufficient to eliminate all except ∼ 0.1% of the less favored variant. This has interesting consequences in the context of the theory. A detailed understanding of the mechanisms for this example requires information about nanostructures that develop on the miscut Nb (011) surface. State-of-the-art information about novel substrate nanostructures, derived from scanning probe and low energy electron microscopies, is presented, and the prospects for a predictive science of variant control in heteroepitaxial growth are assessed.