Growth of single-crystal Nb films.

High-quality single-crystal Nb films with the thickness of 2000Å have successfully been grown epitaxially on single-crystal sapphire (α-Al2O3) and MgO substrates by using an electron-beam evaporation technique. High energy electron diffraction and X-ray diffraction studies have indicated that the Nb (100) plane parallel to the Al2O3 (1102) and MgO (100) Planes, and the Nb (110) plane parallel to the Al2O3 (0001) plane are obtained. The single-crystal Nb films obtained have sufficiently high Tc values and larger resistance ratios (R300/R10=20 -200) than the existing Nb films. On the other hand, single-crystal Nb films have failed to grow on single-crystal quartz substrates, and polycrystal Nb films have showed an increase in lattice constant and a decrease in Tc above a substrate temperature of 500°C. Auger electron spectroscopic (AES) analysis has showed that a reactive interdiffusion occurred in an interfacial region between the deposited Nb film and the quartz substrate, which may prevent epitaxial growth of the Nb films.