Xingtang Zhang

ZnO nanowire Schottky barrier ultraviolet photodetector with high sensitivity and fast recovery speed

ZnO nanowire (NW) ultraviolet (UV) photodetectors have high sensitivity, while the long recovery time is an important limitation for its applications. In this paper, we demonstrate the promising applications of ZnO NW Schottky barrier as high performance UV photodetector with high sensitivity and fast recovery speed. The on/off ratio, sensitivity, and photocurrent gain are 4 × 105, 2.6 × 103 A/W, and 8.5 × 103, respectively. The recovery time is 0.28  s when photocurrent decreases by 3 orders of magnitude, and the corresponding time constant is as short as 46 ms. The physical mechanisms of the fast recovery properties have also been discussed.

Surface states dominative Au Schottky contact on vertical aligned ZnO nanorod arrays synthesized by low-temperature growth

Vertical aligned ZnO nanorod (diameter = 50 nm) arrays on indium tin oxide (ITO) substrates have been grown using a new two-step soft chemical procedure. The resulting current-voltage (I-V) characteristics of the ZnO nanorods exhibited a clear rectifying behaviour. This rectifying behaviour was attributed to the formation of a Schottky contact between the Au coated atomic force microscopy (AFM) tip and ZnO nanorod (nano-M/SC) which was dominated by the surface states in ZnO itself. Photo-assisted conductive AFM (PC-AFM) was used to demonstrate how the I-V characteristics are influenced by the surface states. Our I-V results also showed that the nano-M/SCs had a good photo-electric switching effect at reverse bias.

Template synthesis and characterization of WO3/TiO2 composite nanotubes

Highly ordered WO3/TiO2 composite nanotubes have been successfully prepared by the combination of the sol?gel chemical method and the anodic aluminium oxide (AAO) templating method. The diameter of the WO3/TiO2 composite nanotubes is about 100?nm, which is in good agreement with the pore diameter of the AAO template. The composite nanotubes are composed of mixed oxides of W6+ and Ti4+.

Effect of oxygen stoichiometry on the insulator-metal phase transition in vanadium oxide thin films studied using optical pump-terahertz probe spectroscopy

Using optical pump-terahertz probe spectroscopy, we studied the dynamic behaviors of photoinduced insulator-metal phase transition in vanadium oxide thin films with different oxygen stoichiometry. We found that the insulator-metal phase transition of vanadium dioxide is very sensitive to oxygen stoichiometry: the increased oxygen content in vanadium oxide will reduce the magnitude of phase transition and change the dynamics of the phase transition. The transient complex photoconductivity of vanadium oxide thin films is investigated and analyzed with Drude-Smith model, supplying insight of the dynamic process of phase transition in vanadium oxide thin films.

A study of poly (N-vinylcarbazole) adsorbed on silver surface by SERS

Abstract Surface-enhanced Raman scattering (SERS) spectrum of poly ( N -vinylcarbazole) (PVC) adsorbed on silver surface and the adsorbent structure of PVC have been studied for the first time. The results and discussion show that PVC molecules are strongly adsorbed on the silver surface through benzene ring and hetero-five-membered ring and are possibly oxidized by the silver active surface.

Modulating the surface states of electric field assembled CuO nanowires by electrochemical deposition method

In this paper, the electrochemical deposition and anneal method has been developed to modulate the contact performance of electric field assembled CuO nanowires. After modulation, the current increases about two orders. The I-V curves indicate that before and after modulation, the current transport properties are both dominated by the reverse current of Schottky barriers under image force model. The current increase results from the formation of another current pathway, i.e., the CuO nanowire@nanoparticles/Pt electrode structure, in which the surface states in metal-semiconductor interface are largely reduced by passivating dangling bonds, and the barrier height decreases about 105 meV.

A STUDY ON THE LANGMUIR–BLODGETT (LB) FILMS OF C60/POLY (N-VINYLCARBAZOLE) (PVK) POLYMERS

The Langmuir–Blodgett (LB) films of Poly (N-vinylcarbazole) (PVK) Polymers and its hybrid films with arachidic acid (AA) and C60 were prepared by a vertical deposition method. Atomic Force Microscopy (AFM) and UV-Vis absorption spectroscopy were used to investigate the assembly of PVK/AA and PVK/C60/AA LB films. It was found that the C60 molecules could be aggregated into smaller particles on the base of PVK polymers. The photoluminescence (PL) of PVK was dramatically quenched resulting from the electron transfer from PVK to C60 in their composite films.

A direct investigation of photocharge transfer across monomolecular layer between C60 and CdS quantum dots by photoassisted conductive atomic force microscopy

The composite assembly of C60 and CdS Quantum Dots (QDs) on ITO substrate was prepared by Langmuir-Blodgett (LB) technique using arachic acid (AA), stearic acid (SA) and octadecanyl amine (OA) as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V) measurements on both the CdS QDs and the composite assembly of C60/CdS. The result make it clear that the CdS, C60/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

SYNTHESIS AND CHARACTERIZATION OF DIFFERENT MORPHOLOGICAL LITHIUM TITANATE

Lithium titanate powders of different morphologies were synthesized by improved hydrothermal technique, which was performed at 90°C and atmospheric pressure for 20 h. By changing the solution in the reaction, nanoparticles, flowers petal-like structures, and nanorods of lithium titanate have been obtained, especially nanoparticles with well-crystalline structures were obtained. The morphology and micro-structure of the as-synthesized products were characterized using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and selected-area electron diffraction (SAED).

TEMPLATE SYNTHESIS OF ALIGNED SiO2 SUBMICRO-WIRES

Aligned silicon dioxide (SiO2) submicro-wires have been synthesized from tetraethyl orthosilicate (TEOS) by anodic aluminum oxide (AAO) template method. The products were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD).