Growth of Ni layers on single crystal sapphire substrates

Ni single crystal films have been grown by sputtering on the (0001) basal plane of sapphire varying temperature, flux and substrate bias. In the full parameter range epitaxial growth was observed by transmission electronmicroscopy. The (111) planes of fcc single crystal Ni grow parallel to the substrate surface. Surprisingly, two alternative planes of Ni were parallel to the sapphire (10-10) planes in different domains, either the nickel {110} planes (A orientation) or its {211} planes (B orientation). In all cases twinned areas appeared in both domains. Changing the flux, the temperature and the bias, it was possible to vary the ratio of the two orientations and to reach that only one orientation remained in a given sample. The phenomenon can be explained by differences in cohesion and elastic strain in the two domains. (C) 2013 Elsevier B.V. All rights reserved.