Improvement and protection of niobium surface superconductivity by atomic layer deposition and heat treatment
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(a) Conductance curves measured at 1.7 K on a polycrystalline Nb sample coated with 3 nm of . (b) Corresponding XPS spectrum of the core level. Each color and symbol correspond to one temperature: in blue squares, in green triangles, in orange circles, and in red stars. (c) Ten conductance curves measured on a coated Nb single crystal (110) baked at for 24 h. The curves have been shifted by 0.5 for more clarity and the corresponding zero conductance references for each curve is represented by short lines around the Fermi level .
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(a) Evolution of the superconducting gap (green squares) and inelastic scattering parameter (red circles) as a function of the baking temperature. (b) Plot of the intensity of Nb oxide peaks extracted from XPS fits, the solid black line represents the total intensity of oxide peaks, in red squares are the NbO peak intensity, blue triangles the and in green circles the ones. (c) Schematic evolution of the oxide composition at the surface of Nb. The various shades account for the gradual transition between two different oxides composition, as the corresponding interfaces are rather blurred and continuous than abrupt and well ordered.12
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