Microstructure and Superconductivity of Zn and Au-Sn Junction Nanowires

In this report, we investigated the fabrication, structural characterization, and transport properties of Zn and Au-Sn junction nanowires with diameters ranging from 40 to 100 nm. Both nanowires were fabricated by electro-depositing metals into commercially available polycarbonate (PC) or anodic aluminum oxide (AAO) membranes. Zn nanowire could be single-crystal or polycrystalline by controlling the electro-deposition process. Transport studies have shown that the superconducting transition temperature T _c is insensitive to the nanowire diameter and morphology. The superconductivity shows a clear crossover from bulk-like to quasi-1d behavior when the diameter of the wires is reduced to 70 nm (20 times smaller than the bulk coherence length). The Au/Sn junction nanowires, which consist of two intermetallic phases, AuSn and AuSn₄, have shown three superconducting transitions corresponding to pure Sn, AuSn, and AuSn₄. Mechanisms for the formation of these intermetallic phases and the effect of these phases on the superconductivity of striped nanowires are also discussed.