Zuliang Du

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.

Preparation of Highly Crystalline TiO 2 Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal- structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton

Highly crystalline TiO2 nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO2/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO2 nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO2 nanostructures with various crystalline phases and morphologies were proposed.

Synthesis and assembly of monodisperse spherical Cu2S nanocrystals.

High-quality monodisperse Cu(2)S nanocrystals (sizes from 2 nm to 20 nm) have been successfully synthesized by the reaction of copper stearate (CuSt(2)) and dodecanethiol (DDT) in 1-octadecene (ODE). The nanocrystals were characterized using X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), and transmission electron microscopy (TEM). These as-prepared Cu(2)S nanocrystals with certain sizes have been found with good self-assembly behaviors, and they were easily to assemble into two-dimensional and three-dimensional superlattice structures. DDT served as both sulfur source and capping ligand, and was found a key factor to affect the growth and the self-assembly behaviors of the Cu(2)S nanocrystals.

Roles of defects and grain sizes in photoluminescence of nanocrystalline SrTiO3

Nanocrystalline SrTiO3 was prepared by a stearic acid sol-gel technique. X-ray measurements showed that the sample obtained is of good quality and the grain sizes range from 26 to 120 nm. One blue photoluminescence (PL) band at around 470 nm was observed at room temperature. Investigation of the dependence of the visible emission band on annealing temperatures and grain sizes showed that the effects of grain size and dielectric confinement play important roles, and that oxygen vacancies may act as the radiative centres responsible for the observed visible emission band. The mechanism for the luminescence is explained within the framework of self-trapped excitons.

Effect of Highly Ordered Single-Crystalline TiO2 Nanowire Length on the Photovoltaic Performance of Dye-Sensitized Solar Cells

One-dimensional semiconductor nanostructures grown directly onto transparent conducting oxide substrates with a high internal surface area are most desirable for high-efficiency dye-sensitized solar cells (DSSCs). Herein, we present a multicycle hydrothermal synthesis process to produce vertically aligned, single crystal rutile TiO(2) nanowires with different lengths between 1 and 8 μm for application as the working electrode in DSSCs. Optimum performance was obtained with a TiO(2) nanowire length of 2.0 μm, which may be ascribed to a smaller nanowire diameter with a high internal surface area and better optical transmittance with an increase in the incident light intensity on the N719 dye; as well as a firm connection at the FTO/TiO(2) nanowire interface.

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.

Solution Fabrication and Photoelectrical Properties of CuInS2 Nanocrystals on TiO2 Nanorod Array

One-dimensional semiconductor architectures are receiving attention in preparing photovoltaic solar cells because of its superior charge transport as well as excellent light-harvesting efficiency. In this study, vertically aligned single-crystalline TiO(2) nanorods array was grown directly on transparent conductive glass (FTO), and then CuInS(2) nanocrystals were deposited on nanorods array by spin coating method to form TiO(2)/CuInS(2) heterostructure films. The resulting nanostructure assembly and composition was confirmed by field-emission scanning electron microscope (FESEM) , transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction(XRD). Ultraviolet-visible absorption spectroscopy (UV-vis) data indicates that the absorbance of the nanocomposite film extended into the visible region compared with bare TiO(2) nanorod arrays. The surface photovoltage spectra (SPS) also showed a new and enhanced response region corresponding to the absorption spectrum. These results suggest that the novel CuInS(2) nanocrystals sensitized TiO(2) nanorod array on FTO photoelectrodes has a potential application in photovoltaic devices.

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+.

Analysis of Raman modes in Mn‐doped ZnO nanocrystals

Mn-doped ZnO was synthesized using a co-precipitation technique. X-ray diffraction (XRD) measurements and photoluminescence (PL) spectra show that Mn ions are doped into the lattice positions of ZnO. The modes at 202, 330, and 437 cm -1 in the Raman spectrum are assigned as 2E 2 (low), E 2 (high)-E 2 (low), and E 2 (high) modes of ZnO base, respectively. The mode at 528cm -1 is ascribed to a local vibrational mode related to Mn. The mode at 580cm -1 should be an intrinsic mode of ZnO and assigned to E 1 longitudinal optical (LO). Its reinforcement should result from a combination of resonance at the excitation wavelength and impurity-induced scattering.

The unsaturated photocurrent controlled by two-dimensional barrier geometry of a single ZnO nanowire Schottky photodiode

In this letter, the I-V curve of a single ZnO nanowire assembled by dielectrophoresis was measured, which indicated that a back-to-back Schottky barrier structure was formed. Under ultraviolet light illumination, the photocurrent of the ZnO nanowire Schottky photodiode was unsaturated, and its differential conductivity increased with the increase of bias. A two-dimensional Schottky barrier geometry model was introduced to describe the separation of photogenerated electron-hole pairs in the depletion layer, which can well explain the unsaturated photocurrent property. In addition, the corresponding photocurrent equation was obtained, which was in good agreement with the experimental results.