Abstract
Ni epitaxial films are prepared by ultrahigh vacuum rf magnetron sputtering on Ru underlayers of (1120), (1100), and (0001) grown hetero-epitaxially on MgO single-crystal substrates of (100), (110), and (111) orientations, respectively. The film growth behavior and the crystallographic properties are studied by in-situ reflection high energy electron diffraction and pole figure X-ray diffraction. Metastable hcp-Ni(1120) and hcp-Ni(1100) crystals respectively nucleate on Ru(1120) and Ru(1100) underlayers, where the hcp crystals are stabilized through hetero-epitaxial growth. With increasing the film thickness, the hcp structure in the Ni films starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001) close-packed plane. The resulting films consist of hcp and fcc crystals. On the other hand, only fcc crystal formation is observed for the Ni film grown on Ru(0001) underlayer.