PROPERTIES OF Nb3Al THIN FILMS SPUTTER-DEPOSITED ON SAPPHIRE SUBSTRATES.

Metallurgical phases, lattice constants and superconducting T//c's have been investigated, for Nb//3Al thin films prepared by magnetron sputtering on various sapphire substrates, including poly-crystal and single-crystals with different orientations. Homogeneous thin films with a single-phase Al5 structure and T//c's higher than 16 K can be prepared on poly-crystal, single-crystal (1102) plane and (0001) plane. The differences in the kinds of substrates and even surface crystal orientations change the Al5 phase boundary, as well as the film growth orientations. Films deposited on the (0001) plane have a single-phase Al5 structure even at nearly stoichiometric composition. Films of less than 100 nm thickness show systematic T//c decreases and lattice constant increases. This result suggests the important role of the homoepitaxial growth mechanism in the formation of high-T//c metastable Nb//3Al in the preparation method.