Control of heteroepitaxial stacking by substrate miscut

We report studies of fcc epitaxial crystals, grown on Nb(110), in which the Nb surface offers a template for selection between the two alternative stackings, ABCA{} and ACBA{} of the fcc close-packed planes. The Nb templates were grown epitaxially about 500 {} thick on sapphire (112{}0), and the fcc material studied was Cu₃Au. From symmetry it is not possible for the perfect bcc (110) surface to cause any such selection, which is here attributed instead to vicinal miscut: the logarithm of the stacking ratio must be even in miscut along [001] and odd in miscut along [11{}0]. We find that the measured selectivity is small for miscuts less than about 0.5^∘{}, but approaches a factor 10³ for miscuts along [11{}0] greater than about 1^∘{}. A mechanism for the selection process is discussed in terms of fingered mesostructures that grow on Nb(110) in this regime, as observed first by Zhou, Bonham, and Flynn.