Observation of a discontinuous transition from strong to weak localization in 1D granular metal wires

Dramatic enhancement of superconductivity in single-crystalline nanowire arrays of Sn

Sn is a classical superconductor on the border between type I and type II with critical temperature of 3.7 K. We show that its critical parameters can be dramatically increased if it is brought in the form of loosely bound bundles of thin nanowires. The specific heat displays a pronounced double phase transition at 3.7 K and 5.5 K, which we attribute to the inner ‘bulk’ contribution of the nanowires and to the surface contribution, respectively. The latter is visible only because of the large volume fraction of the surface layer in relation to the bulk volume. The upper transition coincides with the onset of the resistive transition, while zero resistance is gradually approached below the lower transition. In contrast to the low critical field H_c = 0.03 T of Sn in its bulk form, a magnetic field of more than 3 T is required to fully restore the normal state.

Superconductor-insulator transition in quasi-one-dimensional single-crystal Nb₂PdS₅ nanowires

Superconductor-insulator transition (SIT) in one-dimensional (1D) nanowires attracts great attention in the past decade and remains an open question since contrasting results were reported in nanowires with different morphologies (i.e., granular, polycrystalline, or amorphous) or environments. Nb2PdS5 is a recently discovered low-dimensional superconductor with typical quasi-1D chain structure. By decreasing the wire diameter in the range of 100-300 nm, we observed a clear SIT with a 1D transport character driven by both the cross-sectional area and external magnetic field. We also found that the upper critical magnetic field (Hc2) decreases with the reduction of nanowire cross-sectional area. The temperature dependence of the resistance below Tc can be described by the thermally activated phase slip (TAPS) theory without any signature of quantum phase slips (QPS). These findings demonstrated that the enhanced Coulomb interactions with the shrinkage of the wire diameter competes with the interchain Josephson-like coupling may play a crucial role on the SIT in quasi-1D system.

Graphene oxide-templated synthesis of ultrathin or tadpole-shaped au nanowires with alternating hcp and fcc domains

Ultrathin Au nanowires (AuNWs) and tadpole-shaped nanowires are synthesized on graphene oxide (GO) sheet templates. For the first time, 1.6 nm-diameter AuNWs are shown to contain hexagonal close-packed (hcp) crystal domains, and the tadpole-shaped nanowires exhibit alternating sets of hcp and face-centered cubic (fcc) structures, associated with variation in wire thickness.

The creation of nanojunctions

This review describes recent progress in creation of nanojunctions between individual nanoobjects. The accomplishments of various strategies used for nanojunction creation are highlighted and the corresponding challenges are discussed. The possible ongoing development for the creation of device-oriented nanojunctions is speculated upon.

Proximity-induced superconductivity in nanowires: minigap state and differential magnetoresistance oscillations

We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the minigap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We suggest that the minigap phase as well as the periodic oscillations originate from a coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or the application of a magnetic field.

One-dimensional nanostructures of metals: large-scale synthesis and some potential applications

We review recent developments in our group regarding the solution-phase synthesis of one-dimensional nanostructures of metals. The synthetic approaches include solution-liquid-solid growth for nanowires of low-melting-point metals such as Pb; seed-directed growth for Ag nanowires, nanobeams, and nanobelts; kinetically controlled growth for Pt nanorods, nanowires, and multipods; and galvanic replacement for nanotubes of Au, Pt, and Pd. Both characterization and mechanistic studies are presented for each nanostructure. Finally, we highlight the electrical and plasmonic properties of these metal nanostructures and discuss their potential applications in nanoscale devices.

Nanostructures of Sn and their enhanced, shape-dependent superconducting properties

A noncatalytic and template-free vapor transport process was developed to make possible simultaneous growth of single-crystalline tin nanowires, nanosquares, nanodisks, and polycrystalline nanoparticles. The formation of such a rich variety of morphologies in a single growth experiment can be attributed to variations in the growth rate among different crystallographic planes when employing the vapor-solid growth mechanism. Structural characterization with high-resolution transmission electron microscopy reveals a preferential growth direction of [100] in Sn nanowires, nanosquares, and nanodisks. Shape-dependent superconducting properties are observed. These four types of Sn nanostructures all show typical diamagnetic behavior in magnetization measurements, with the three anisotropically shaped nanostructures (nanowires, nanosquares, and nanodisks) showing one order of magnitude enhancement in the working magnetic field ranges for superconductivity, compared to bulk Sn and Sn nanoparticles. The magnetic field range is broadest for nanowires, followed by nanodisks, nanosquares, and nanoparticles.

Nanometer-scale modification and welding of silicon and metallic nanowires with a high-intensity electron beam

We demonstrate that a high-intensity electron beam can be applied to create holes, gaps, and other patterns of atomic and nanometer dimensions on a single nanowire, to weld individual nanowires to form metal-metal or metal-semiconductor junctions, and to remove the oxide shell from a crystalline nanowire. In single-crystalline Si nanowires, the beam induces instant local vaporization and local amorphization. In metallic Au, Ag, Cu, and Sn nanowires, the beam induces rapid local surface melting and enhanced surface diffusion, in addition to local vaporization. These studies open up a novel approach for patterning and connecting nanomaterials in devices and circuits at the nanometer scale.

Spontaneous shape distortion in quench-condensed bismuth clusters below 8 K

We study single-electron transport in quench-condensed bismuth films. By lateral confinement, we select a specific cluster of about 10(3) atoms and use tunneling barriers that appear naturally during thin-film formation. A remarkable reversible increase of the sample conductance up to 5 times was found as the temperature was lowered from 11 to 4 K. We attribute this effect to a spontaneous distortion of the cluster shape and discuss its relation to a phase transition predicted for free metallic clusters.