Metallic nanowires (Au, Ag, Cu, Ni, Co, and Rh) with an average diameter of 40 nm and a length of 3-5 μm have been fabricated by electrodeposition in the pores of track-etched polycarbonate membranes. Structural characterizations by transmission electron microscopy (TEM) and electron diffraction showed that nanowires of Au, Ag, and Cu are single-crystalline with a preferred [111] orientation, whereas Ni, Co, and Rh wires are polycrystalline. Possible mechanisms responsible for nucleation and growth for single-crystal noble metals versus polycrystalline group VIII-B metals are discussed.

Electrical transport measurements were made on single-crystal Sn nanowires to understand the intrinsic dissipation mechanisms of a one-dimensional superconductor. While the resistance of wires of diameter larger than 70 nm drops precipitately to zero at T c near 3.7 K, a residual resistive tail extending down to low temperature is found for wires with diameters of 20 and 40 nm. As a function of temperature, the logarithm of the residual resistance appears as two linear sections, one within a few tenths of a degree below T c and the other extending down to at least 0.47 K, the minimum temperature of the measurements. The residual resistance is found to be ohmic at all temperatures below T c of Sn. These findings are suggestive of a thermally activated phase slip process near T c and quantum fluctuation-induced phase slip process in the low temperature regime. When the excitation current exceeds a critical value, the voltage-current (V-I) curves show a series of discrete steps in approaching the normal state. These steps cannot be fully understood with the classical Skocpol-Beasley-Tinkham phase slip center model (PSC), but can be qualitatively accounted for partly by the PSC model modified by Michotte et al. PACS numbers: 74.78.Na, 73.63.Nm When the diameter of a superconducting wire is smaller than the phase coherence length, ξ (T), its behavior is expected to deviate from that of bulk and crosses over towards that expected of a quasi onedimensional (1d) system. In spite of extensive experimental studies over the last three decades, there are still controversies on what are the expected properties of a 1d superconductor [1][2][3][4][5][6] . A major reason for the uncertainties is the variety of microstructure and morphology of the samples used in the experiments. Indeed, contrasting results are found in granular 1 , polycrystalline 2 and amorphous wires 3-6 fabricated by sputtering or evaporating techniques. Measurements on single-crystal nanowires with uniform diameter would be ideal to single out the effect of 1d confinement. To date, such measurements were carried out only on crystalline superconducting whiskers with diameters ranging from 0.1 to 0.8 µm 7-10 . At such a length scale, 1d behavior is unlikely to be evident except at temperatures very close to T c .In this paper we present a systematic study of the transport properties of single-crystal cylindrical tin (Sn) nanowires with diameters between 20 and 100 nm. We chose tin in our study because the coherence length of bulk tin is relatively long (ξ (0)~200 nm) and singlecrystal nanowires of uniform diameter can be consistently prepared by a simple template-assembly technique 11 . Our results show a clear crossover from bulk-like to probably quasi 1d-like behavior when the diameter of the wires is reduced to 40 nm (5 times smaller than the bulk coherence length). Two different dissipative processes, i.e., thermally activated phase slip (TAPS) close to T c and quantum phase-slip (QPS) at temperatures far below T c are clearly observed for the wires ...

Single-crystal superconducting tin nanowires with diameters of 40–160 nm have been prepared by electrochemical deposition in porous polycarbonate membranes. Structural characterization through transmission electron microscopy and x-ray diffraction showed that the nanowires are highly oriented along the [100] direction. Although the superconducting transition temperature is close to the bulk value of 3.7 K, the effect of reduced dimensionality is clearly evident in the electrical transport properties of the thinnest wires (40 nm diameter). Magnetization measurements show that the critical field of the nanowires increases significantly with decreasing diameter to ∼0.3 T for the thinnest wires, nearly an order of magnitude larger than the bulk value.

Transport measurements were made on a system consisting of a zinc nanowire array sandwiched between two bulk superconducting electrodes (Sn or In). It was found that the superconductivity of Zn nanowires of 40 nm diameter is suppressed either completely or partially by the superconducting electrodes. When the electrodes are driven into their normal state by a magnetic field, the nanowires switch back to their superconducting state. This phenomenon is significantly weakened when one of the two superconducting electrodes is replaced by a normal metal. The phenomenon is not seen in wires with diameters equal to or thicker than 70 nm.

We present heat capacity measurements on crystalline Zn nanowires with diameters of 230 and 23 nm, bracketing the superconducting coherence length of 155 nm. Transport measurements on superconducting nanowires have found a crossover from three-dimensional to one-dimensional behavior as the wire diameter was reduced below the coherence length. In contrast, the normalized heat capacity peak of the 23 nm Zn nanowires is found to be nearly identical to that of 230 nm wires and bulk Zn, indicating their thermodynamic properties remain three dimensional.