S.Z. Wang

YBaCuO superconducting thin films with zero resistance at 84 K by multilayer deposition

YBaCuO superconducting thin films were prepared by multilayer deposition on different kinds of substrates. High Tc with an onset of 94 K and a zero resistance at 84 K has been obtained by deposition on pure ZrO2 substrates. The nature of zero resistance as well as the dR/dT characteristic above Tc and the influence of substrates are discussed.

High-performance n-type carbon nanotube field-effect transistors with estimated sub-10-ps gate delay

High-performance top-gated n-type single-walled carbon nanotube (CNT) field-effect transistors (FETs) have been fabricated using scandium contacts and HfO2 gate oxide and are benchmarked against the state-of-the-art n-type Si metal-oxide semiconductor FETs. Two key device metrics, the intrinsic gate-delay (CV∕I) and energy-delay product (CV∕I⋅CV2) per unit width, of the n-type CNT FETs are found to show significant improvement over the Si devices. In particular, the gate-delay time is estimated to be 2.1ps for an n-type CNT FET which is based on a CNT with a diameter of 1.1nm and a channel length of 220nm.

Epitaxial growth of superconducting YBa2Cu3O7−x thin films by reactive magnetron sputtering

Perfect epitaxial growth of superconducting YBa2Cu3O7−x thin films have been achieved on (100)u2009SrTiO3, (110)u2009SrTiO3, and (100)u2009ZrO2 substrates using a modified planar dc magnetron sputtering system. The films exhibit zero resistances at 87–90 K with transition widths of about 2 K. The critical current density of 1.4×106 A/cm2 at 77 K so far has been measured on the (100)u2009SrTiO3 substrate. The epitaxial orientation of the thin films was influenced by the substrate orientation, the substrate temperature, and the oxygen partial pressure. The quality of growth and the epitaxial orientation of the films were examined by electron channeling, x‐ray diffraction, and reflection high‐energy electron diffraction techniques. The preferential epitaxial orientation is discussed.

Fabrication of high performance top-gate complementary inverter using a single carbon nanotube and via a simple process

High performance complementary inverters have been fabricated using single-walled carbon nanotubes. The Al2O3 top-gate dielectric is grown via first depositing an Al film followed by complete oxidation of the film. It is shown that the quality of the Al2O3 film can be significantly improved by annealing at 400°C, and stable p-type and n-type carbon nanotube field-effect transistors (CNTFETs) may be fabricated using either Pd (p-type) or Al (n-type) electrodes. High performance complementary inverter is demonstrated by integrating the p-type and n-type CNTFETs on the same carbon nanotube, and a gain of about 3.5 is achieved.

Preparation and Catalytic Activity of Monolayer-Dispersed Pt/Ni Bimetallic Catalyst for C=C and C=O Hydrogenation

Abstract The monolayer-dispersed Pt/Ni bimetallic catalyst was prepared through a simple replacement reaction, and its catalytic activity for the hydrogenation of cyclohexene, styrene, acetone, and butyl aldehyde was also tested. The Pt/Ni catalyst that was prepared by the replacement reaction showed much higher activity than Pt/Ni and Pt/Al 2 O 3 catalysts with the same Pt loading prepared by the conventional impregnation method.

High misfit epitaxial growth: Superconducting YBa2Cu3O7−x thin films on (100)BaF2 substrates

In situ epitaxial growth of YBa2Cu3O7−x superconducting thin films on (100)BaF2 substrates has been successful by an off‐axis dc planar magnetron sputtering method. The zero‐resistance temperatures of these thin films are about 81–84 K with transition width of 1.5 K. The characteristics of the films were examined by x‐ray diffraction, reflection high energy electron diffraction, Rutherford backscattering spectroscopy ion channeling techniques, and scanning electron microscopy. The experimental results suggest that BaF2 is a promising material as substrates or buffer layers for the epitaxial growth of high Tc superconducting thin films, especially in high frequency applications. Discussions on the heteroepitaxy of the YBCO/BaF2 system are propounded.

High misfit epitaxial growth: Superconducting YBa sub 2 Cu sub 3 O sub 7 minus sub x thin films on (100)BaF sub 2 substrates

In situ epitaxial growth of YBa2Cu3O7−x superconducting thin films on (100)BaF2 substrates has been successful by an off‐axis dc planar magnetron sputtering method. The zero‐resistance temperatures of these thin films are about 81–84 K with transition width of 1.5 K. The characteristics of the films were examined by x‐ray diffraction, reflection high energy electron diffraction, Rutherford backscattering spectroscopy ion channeling techniques, and scanning electron microscopy. The experimental results suggest that BaF2 is a promising material as substrates or buffer layers for the epitaxial growth of high Tc superconducting thin films, especially in high frequency applications. Discussions on the heteroepitaxy of the YBCO/BaF2 system are propounded.

Measuring the electrical characteristics of individual junctions in the SnO2 capped ZnO nanowire arrays on Zn substrate

Direct measurements on electrical characteristics have been carried out in situ inside a scanning electron microscope using a multiple nanoprobe system on individual SnO2 capped ZnO nanowires (NWs) within a NW film on a Zn substrate. It is shown that while good Ohmic contacts can be made at Zn–ZnO NW and ZnO NW–SnO2 cap (when heavily doped with Zn) junctions, the overall I-V characteristics of the Zn–ZnO–SnO2 junction system differ significantly among different NWs, suggesting doping inhomogeneity in the NW film.

Thermally activated flux motion in epitaxial YBCO films

Abstract We systematically studied the resistive transition and the voltage-current characteristics of well epitaxially grown single-crystalline YBCO films and found two important features of magnetic-flux motion in high T c superconductors: 1. 1) Isothermal V-I curves can show both positive and negative curvatures simultaneously. This inflecting behavior may be explained by some nonlinearity effects in flux creep. 2. 2) The activation volume of the flux creep is temperature-dependent as [T-T c ] −3v with v~0.6 This behavior strongly hints that flux creep is related to the fluctuation below critical point of secondary phase transition. A modified model for flux motion is proposed.

Epitaxial feature of Y-Ba-Cu-O thin films prepared by multilayer deposition

Y-Ba-Cu-O thin films have been prepared on (100) SrTiO/sub 3/ substrates by multilayer deposition technique using a single electron beam source. The epitaxial growth with a-axis normal to the film plane was confirmed by X-ray diffraction. The oriented growth phenomenon of the Y-Ba-Cu-O thin films is explained by theories of epitaxy and texture.