High quality and large-scale manually operated monolayer graphene pasters.

Graphene is a well-known material with various potential applications. Here we report the manufacture of high-quality and large-scale monolayer graphene pasters via polyvinyl butyral (PVB). These pasters have good self-supporting properties and overcome the drawback of weak mechanical strength of PMMA. Manual manipulations to monolayer graphene become realizable via graphene pasters. Graphene pasters can be quickly diverted onto any substrate with sufficient contact and greatly minimize the challenges in graphene transfer, measurements, and other applications. The improved transfer process via graphene pasters protects the integrity of monolayer graphene and introduces few cracks or tears into graphene. Large-scale monolayer graphene films diverted onto SiO2/Si by using graphene pasters maintain low resistivity and low Dirac point, while also exhibiting a higher magnetoresistance than traditional results. High magnetoresistance up to 600% and signs of saturation at high magnetic fields can be seen. Obvious negative magnetoresistance at low magnetic fields due to weak localization also can be observed. Graphene pasters can be used in many different domains and will promote future studies and applications of graphene.

Magnetization and electric transport properties of single-crystal MgB2 nanowires.

High quality single-crystal magnesium diboride (MgB(2)) nanowires with lengths exceeding 10 µm were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB(2) nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current-voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB(2) NWs.

MgB2 superconducting whiskers synthesized by using the hybrid physical-chemical vapor deposition.

In this work, MgB(2) whiskers were fabricated on a copper substrate by using the hybrid physical-chemical vapor deposition, which was one of the most effective ways to make high quality pure MgB(2) films, with the possible growth mechanism discussed. The whiskers are hexagonal and conelike and grow along the [0001] direction with a single-crystal structure. The onset transition temperature is approximately 39 K, which is among the best in the published nanostructure MgB(2) papers. Fabrication of nanoscale MgB(2) whiskers provides the fundamental understanding of the effect of dimensionality and size on superconductivity.

Low-temperature mass production of superconducting MgB2 nanofibers from Mg(BH4)2 decomposition and recombination.

Massive superconducting MgB(2) nanofibers are obtained for the first time from Mg(BH(4))(2). The technique optimizes reaction conditions to only 1 h at 460 °C and provides nanofibers which exhibited satisfying superconducting properties. The morphology transformation according to temperature changes and the special mechanism of precursor inductive synthesis are discussed.

Fully band-resolved scattering rate in MgB2 revealed by the nonlinear hall effect and magnetoresistance measurements.

We have measured the normal state temperature dependence of the Hall effect and magnetoresistance in epitaxial MgB2 thin films with variable disorders characterized by the residual resistance ratio RRR ranging from 4.0 to 33.3. A strong nonlinearity of the Hall effect and magnetoresistance have been found in clean samples, and they decrease gradually with the increase of disorders or temperature. By fitting the data to the theoretical model based on the Boltzmann equation and ab initio calculations for a four-band system, for the first time, we derived the scattering rates of these four bands at different temperatures and magnitude of disorders. Our method provides a unique way to derive these important parameters in multiband systems.