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Abstract Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium–tin (Nb3Sn)in situunder different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb3Sn surface structures for high-performance superconducting RF and quantum applications.
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This content will become publicly available on February 5, 2026
Intrinsic Structures and Electrochemical Properties of Floating Zone Grown Nb 12 WO 33 and Nb 14 W 3 O 44 Single Crystals
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We report the growth of AlBN/β‐Nb2N nitride epitaxial heterostructures in which the AlBN is ferroelectric, and β‐Nb2N with metallic resistivity ≈40 μ at 300 K becomes superconducting belowTC ≈ 0.5 K. Using nitrogen plasma molecular beam epitaxy, we grow hexagonal β‐Nb2N films on c‐plane Al2O3substrates, followed by wurtzite AlBN. The AlBN is in epitaxial registry and rotationally aligned with the β‐Nb2N, and the hexagonal lattices of both nitride layers make angles of 30° with the hexagonal lattice of the Al2O3substrate. The B composition of the AlBN layer is varied from 0 to 14.7%. It is found to depend weakly on the B flux, but increases strongly with decreasing growth temperature, indicating a reaction rate‐controlled growth. The increase in B content causes a non‐monotonic change in the a‐lattice constant and a monotonic decrease in the c‐lattice constant of AlBN. Sharp, abrupt epitaxial AlBN/β‐Nb2N/Al2O3heterojunction interfaces and close symmetry matching are observed by transmission electron microscopy. The observation of ferroelectricity and superconductivity in epitaxial nitride heterostructures opens avenues for novel electronic and quantum devices.more » « less
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