Bingqiang Cao

Temperature-dependent shifts of three emission bands for ZnO nanoneedle arrays

The photoluminescence properties of ZnO nanoneedle arrays, grown on silicon substrate by electrodeposition, are studied over the temperatures from 10K to 300K. There exist three emission bands in ultraviolet, violet, and green regions, respectively. With increasing temperature, these bands show different temperature dependences: A normal redshift for the ultraviolet emission, S-shaped shift for the violet emission, and blueshift for the green one. The origins of these three bands and their temperature-dependent shifts are explained based on defect levels (zinc interstitial and oxygen vacancy levels) and carrier localization effect at the defect levels in addition to band-gap shrinkage.

Two-dimensional hierarchical porous silica film and its tunable superhydrophobicity

Base do na monolayer polystyrene (PS) colloidal crystal, large-scale two-dimensional (2D) hierarchical porous silica (orderly arranged macropores and disordered mesopores in its skeleton) with a high specific surface area was fabricated by the sol–gel technique. Such material has demonstrated superhydrophilicity with a water contact angle (CA) of 5 ◦ and superhydrophobicity with a water CA of 154 ◦ after surface modification with fluoroalkylsilane. More interestingly, the water CA can be increased to 165 ◦ using a heat-deformed PS template, which suggests that the superhydrophobicity can be controlled by the template with different heat-deformed extents. Such silica films have applications in fields of adsorbent, catalytic, chromatographic support, microseparator and microfluid devices. (Some figures in this article are in colour only in the electronic version)

A template-free electrochemical deposition route to ZnO nanoneedle arrays and their optical and field emission properties

We report a soft and template-free electrochemical deposition method for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate. It has been shown that the ZnO nanoneedles possess single-crystal wurtzite structure and grow along the c-axis perpendicularly on the substrate. Raman and resonant Raman scattering studies have confirmed that the ZnO nanoneedles are of good crystal quality. The room temperature photoluminescence spectrum of such ZnO nanoneedle arrays exhibits a strong ultraviolet emission but negligible visible emission. The time-resolved photoluminescence spectral analysis discloses the excitonic origin of the ultraviolet emission. The field electron emission study, showing notable emission current in a moderate turn-on field, demonstrates potential applications of such ZnO nanoneedle arrays in field emission display devices. The formation of such a ZnO nanoneedle array is attributed to the formation of {0001}-oriented ZnO nuclei on the oriented gold coated silicon substrate and preferential growth along .

Reactive-Template Fabrication of Porous SnO2 Nanotubes and Their Remarkable Gas-Sensing Performance

A facile reactive-template strategy has been developed to fabricate porous SnO2 nanotubes using MnO2 nanorods as the sacrificial template. The formation of nanotubes is based on the redox reaction mechanism, which requires no post-treatment of the MnO2 templates. The morphological and structural characteristics of the samples have been systematically characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal-gravimetric (TG), and N2 adsorption-desorption techniques. A gas-sensor device was constructed using as-prepared SnO2 nanotubes and was tested for its ability to detect ethanol and some other compounds. Because of the porous structure and relative large specific surface area, the SnO2 nanotube sensor manifests remarkably improved sensing performance, including fast response recovery, high sensitivity, and excellent repeatability, suggesting the promising application of the SnO2 nanotube materials.

Ultraviolet-light-emitting ZnO nanosheets prepared by a chemical bath deposition method

Two-dimensional polar-surface-dominated ZnO nanosheets (nanodiscs) with dimensions of several microns and thickness of tens of nanometres were synthesized in bulk quantity at low temperature (~70??C) by a simple and environmentally benign chemical bath deposition (CBD) method. These ZnO nanosheets are of single-crystal wurtzite structure; they grow along the crystallographic directions within polar {0001} planes. This is different from previous reported films or nanowire arrays prepared by the CBD method. Raman scattering spectrum studies confirm that the as-synthesized nanosheets are of high crystal quality and indicate an optical phonon confinement effect in such ZnO nanosheets. These nanosheets show a sharp intrinsic ultraviolet excitonic emission peak centred at 380?nm at room temperature, have large surface area exposed to the gaseous environment, and could be an ideal ultraviolet light source or objects for the fabrication of nanoscaled devices.

Morphology evolution and photoluminescence properties of ZnO films electrochemically deposited on conductive glass substrates

The current-dependent morphology evolution and photoluminescence properties of zinc oxide (ZnO) films prepared by electrochemical deposition (ECD) method were studied in this paper. It has been shown that the morphologies of ZnO films vary from porous to dense structure, from pillar crystal array to two-dimensional nanosheet covered film, with increase of deposition currents. Correspondingly, orientation of the film evolves from randomly to highly c-axis oriented structure. Current dependence of morphology is attributed to the ECD current-controlled preferential growth velocity along the c axis. All the ZnO films prepared over a wide current range show strong ultraviolet (UV) emission at room temperature, which also shows deposition current dependence in intensity, together with relatively weak defect-related green emission under UV excitations. Further experiments have revealed that a nonradiative relax process and a radiative electron-hole combination process are involved in this defect-related green em...

Surface optical phonon Raman scattering in Zn∕ZnO core-shell structured nanoparticles

Surface optical (SO) phonon vibration mode predominant Raman scattering spectra were observed in the range of 545–565cm−1 in metal-semiconductor Zn∕ZnO core-shell structured nanoparticles, prepared by laser ablation of a zinc target in a surfactant aqueous solution. The SO phonon mode exhibits significant size confinement effect. Such SO dominant Raman scattering is attributed to the existence of a large number of disorderly arranged areas among ultrafine ZnO grains formed under the extreme condition of laser ablation. This study demonstrates that the properties of surface phonons can availably reflect some important physical information.

Fully indium-free flexible Ag nanowires/ZnO:F composite transparent conductive electrodes with high haze

Solution-processed metal nanowires (NWs) and Earth-abundant doped ZnO have been proposed to replace the most widely used indium tin oxide (ITO) transparent and conductive electrode. Generally, there is a dilemma, the trade-off between optical transparency and conductivity for these materials taken alone makes them difficult to compete with commercial ITO. In this work, a modified polyol synthesis method was adopted to grow single-crystal silver nanowire with controlled length by adding AgNO3 solution in advance and using high molecular weight polyvinylpyrrolidone (PVP). Ag nanowires ink was then spin coated onto flexible PET substrate to form Ag NW mesh, which shows impressive transparent and conductive (TC) property with sheet resistance of 23 Ω sq−1 and transmittance of 90.4% at a wavelength of 550 nm. A post fluorine-doped ZnO (FZO) layer was then deposited by pulsed laser deposition method to improve the TC, stability and mechanical property. High-quality Ag NW/FZO composite electrode was finally acquired at room temperature after optimizing the Ag NW length, concentration in suspension, and FZO layer thickness, with transmittance of 83% at wavelength of 550 nm, sheet resistance of 17 Ω sq−1, and high haze of 36.5%. Perovskite solar cells incorporating such Ag NW/FZO composite electrode exhibited a better cell performance compared to the similar FTO-based perovskite solar cells.

Near Room Temperature, Fast-Response, and Highly Sensitive Triethylamine Sensor Assembled with Au-Loaded ZnO/SnO2 Core–Shell Nanorods on Flat Alumina Substrates

Chemiresistive gas sensors with low power consumption, fast response, and reliable fabrication process for a specific target gas have been now created for many applications. They require both sensitive nanomaterials and an efficient substrate chip for heating and electrical addressing. Herein, a near room working temperature and fast response triethylamine (TEA) gas sensor has been fabricated successfully by designing gold (Au)-loaded ZnO/SnO2 core-shell nanorods. ZnO nanorods grew directly on Al2O3 flat electrodes with a cost-effective hydrothermal process. By employing pulsed laser deposition (PLD) and DC-sputtering methods, the construction of Au nanoparticle-loaded ZnO/SnO2 core/shell nanorod heterostructure is highly controllable and reproducible. In comparison with pristine ZnO, SnO2, and Au-loaded ZnO, SnO2 sensors, Au-ZnO/SnO2 nanorod sensors exhibit a remarkably high and fast response to TEA gas at working temperatures as low as 40 °C. The enhanced sensing property of the Au-ZnO/SnO2 sensor is also discussed with the semiconductor depletion layer model introduced by Au-SnO2 Schottky contact and ZnO/SnO2 N-N heterojunction.

Fabrication and Characterization of Beaded SiC Quantum Rings with Anomalous Red Spectral Shift

8 Shapeand size-control of nanocrystals (NCs) is valuable in many aspects of modern science and technology. [ 1–9 ] Wet chemical methods are widely used in the synthesis of metal, metal oxide, and metal sulfi de NCs with various shapes and dimensions in a controllable manner. [ 1–9 ] However, they are unsuitable for the synthesis of carbides and nitrides because of their high melting points (generally > 2000 ° C) as well as a lack of appropriate precursors. Carbide and nitride NCs are of signifi cant interest for biomedical applications and optical devices operated in extreme conditions, because they have high strength and unique optical properties while being chemically inert and biocompatible. [ 10–15 ] The properties of NCs are dependent on not only their constituent materials but also their geometries. Nanorings, for example, are important zero-dimensional nanostructures in many applications and they provide an excellent model to explore quantum-related properties. [ 16–19 ] Their fabrication, however, remains a signifi cant challenge using existing fabrication methodologies. [ 20–22 ]