HYDROGEN ANNEALING OF EPITAXIAL NIOBIUM FILMS ON SAPPHIRE

High-resolution X-ray scattering studies of niobium [10] films grown by molecular beam epitaxy on sapphire [1120BAR] substrates have revealed novel structural features. In transverse scans of the out-of-plane Nb (110) Bragg peak we find two components, the sharper of which implies mosaicities an order of magnitude better than bulk single crystal Nb. The planes associated with the sharp component are aligned with the sapphire (1120BAR) planes. Upon hydrogen loading of the Nb film, we find evidence for a dramatic increase of the lateral coherence length. It appears that the addition of hydrogen may allow defects to move to the film boundary, removing inhomogeneous strain and thus improving the epitaxial film quality by acting as a very effective ''cold-annealing'' agent.