Research in Materials Science: Superconducting Transition Metal Alloys

Good superconductive tunneling has been obtained into Niobium(Aluminum, Germanium) ribbon substrates and sputtered films. Unfortunately, the data is surface limited and represents a disturbed layer of Tc7K. Arc melted buttons of Nb3(Al, Germanium) used as junction substrates have derivative curves which are reminiscent of deformed Nb tunneling data and are, therefore, difficult to interpret. Nb3Sn substrates formed by the diffusion of tin into niobium single crystals yield reproducible junctions with gap values about 3.6 mV; the tunneling characteristics are, however, not ideal. A systematic study of the electronic behavior of arc-evaporated amorphous carbon films as a function of deposition rate, vacuum pressure, film thickness, ageing, and annealing was completed. General fabrication and performance criteria for effective tunneling barriers between a variety of metal and alloy substrates have been established. Superconductive tunneling was observed with electron beam evaporated amorphous carbon barriers on tin, indium, lead-impregnated porous glass, and bulk Nb3 (Al, Ge).