Abstract
Abstract : Low energy ion beam cleaning of the substrates prior to deposition has been found to enhance the quality of ultrathin ( 100A) refractory superconducting Niobium, Vanadium films. Nb film thin as 7A has been grown from which it has been possible to fabricate good superconducting tunnel junctions. Both the native films and the tunnel junctions can be thermally recycled without any degradation. In-situ surface studies along with transmission electron microscopy suggest the removal of the carbon atoms from the surface of the substrate and possibly th e increased chemical reactivity of the substrate atoms are the causes of the improvement. TEM results indicate that the Nb films grow perfectly lattice matched to the sapphire substrate when the substrate is ion-beam cleaned. This strained-layer epitaxy is observed up to 40A, the maximum thickness investigated through TEM. Good-quality tunnel junctions have been fabricated on ultrathin films of Nb. Absolute specific-heat measurements have been made through the metal-insulator transition in thin film Molybdenum (X) Germanium (1-X) determining the thermodynamic electronic density of states. Nb/Tantalum multilayered films prepared by magnetron sputtering have been studied by critical field measurements. The effects of substrate orientation and deposition temperature on the properties of the films has been determined. Considerable progress has been made in the design and construction of the new advance electron beam deposition facility.
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