INTERFACE STRUCTURE AND OVERGROWTH ORIENTATION FOR NIOBIUM AND MOLYBDENUM FILMS ON SAPPHIRE SUBSTRATES .1. A-PLANE SUBSTRATES

We report a comparison of the epitaxies of niobium and molybdenum sput ter deposited on A-plane sapphire substrates. In the niobium case, the cores of the dislocation arrays associated with the interfacial misfi t relief are localized in the metallic overgrowth, some 7 to 9 Angstro m away from the sapphire, and the dislocations adopt standard body-cen tred cubic-type Burgers vectors. For molybdenum, the dislocation array lies very close to the compositional interface. The way this differen ce in interface structure leads to different epitaxial behaviours for the two systems is discussed.