Morphology transition of Ag-doped ZnO nanostructures in hot-walled pulsed laser deposition

We investigate Ag-doped ZnO (SZO) nanostructures grown by a vapor-liquid-solid mechanism in a hot-walled pulsed laser deposition (HW-PLD) that can control the kinetic energy of the laser-ablated particles from a target. After optimizing the process conditions for nanowire (NW) formation, the transition of the morphology from the NW to nanohorn (NH) is observed. The NH morphologies are analyzed in both cases of pure ZnO and SZO to find that the Ag-doping provides the morphological changes of the nanostructures with the doping-induced stress in the nanocrystals. Additional morphology degradations are studied with respect to the target-substrate (T-S) distance illustrating the effect of the kinetic energy and flux changes of the source particles on the nanoshaping.     

Hydrothermal growth of ZnO nanostructures

Abstract

One-dimensional nanostructures exhibit interesting electronic and optical properties due to their low dimensionality leading to quantum confinement effects. ZnO has received lot of attention as a nanostructured material because of unique properties rendering it suitable for various applications. Amongst the different methods of synthesis of ZnO nanostructures, the hydrothermal method is attractive for its simplicity and environment friendly conditions. This review summarizes the conditions leading to the growth of different ZnO nanostructures using hydrothermal technique. Doping of ZnO nanostructures through hydrothermal method are also highlighted.     

Hydrothermal growth of ZnO nanostructures

One-dimensional nanostructures exhibit interesting electronic and optical properties due to their low dimensionality leading to quantum confinement effects. ZnO has received lot of attention as a nanostructured material because of unique properties rendering it suitable for various applications. Amongst the different methods of synthesis of ZnO nanostructures, the hydrothermal method is attractive for its simplicity and environment friendly conditions. This review summarizes the conditions leading to the growth of different ZnO nanostructures using hydrothermal technique. Doping of ZnO nanostructures through hydrothermal method are also highlighted.     

Ga掺杂ZnO电子结构的密度泛函计算

根据密度泛函理论（DFT）,采用“总体能量-平面波”超软赝势方法,对不同的Ga掺杂浓度的ZnO晶体几何结构进行了优化,从理论上给出了Ga掺杂ZnO晶体结构参数及性质,为ZnO材料的掺杂改性研究提供了理论依据。计算了Ga掺杂情况下ZnO晶体的总体能量、能带结构、总体态密度、分波态密度。分析了Ga掺杂对ZnO晶体电子结构和光学吸收带边的影响。     

Hybrid nanostructures of titanium-decorated ZnO nanowires

Hybrid nanostructures of titanium (Ti)-decorated zinc oxide (ZnO) nanowire were synthesized. Various thick Ti films (6 nm, 10 nm, and 20 nm) were coated to form a titanium oxide (TiO) coating layer around ZnO nanowires. Transmission electron microscope analysis was performed to verify the crystallinity and phases of the TiO layers according to the Ti-coating thickness. Under UV illumination, a bare ZnO nanowire showed a conventional n-type conducting performances. With a Ti coating on a ZnO nanowire, it was converted to a p-type conductor due to the existence of electron-captured oxygen molecules. It discusses the fabrication of Ti-decorated ZnO nanowires including the working mechanisms with respect to UV light.     

ZnO一维纳米材料的制备与表征

首先以乙醇为溶剂,乙酸锌为前驱体,油酸钠为表面修饰剂,采用溶液化学法,制得ZnO纳米粒子。以自制ZnO纳米粒子为基体,通过煅烧方法制备针状ZnO纳米线束。通过紫外-可见吸收光谱(UVVis)、荧光光谱(FL)、透射电子显微镜(TEM)、X射线衍射(XRD)和扫描电子显微镜(SEM)等方法对合成的样品进行表征。结果表明,所合成ZnO纳米粒子样品UV-Vis吸收光谱在355nm给出ZnO纳米粒子的特征吸收峰,FL光谱显示在400和550nm处产生荧光发射。ZnO纳米粒子尺寸约为5nm且粒径分布较窄。自制ZnO纳米粒子样品经500℃煅烧后可得到针状ZnO纳米线束。纳米线为六方晶系纤锌矿结构ZnO单晶纳米线,长度约为10μm,直径约为100nm,长径比约为100,且具有良好的紫外发光性能。     

Ag掺杂对ZnO纳米线气敏性能的影响

以采用物理热蒸发法制备的纯ZnO纳米线和Ag掺杂ZnO纳米线为气敏基料，制备成旁热式气敏元件，用静态配气法对浓度均为100ppm的无水乙醇蒸汽、氨气、甲烷及一氧化碳四种气体进行气敏性能测试，结果表明，Ag掺杂后，ZnO纳米线对四种气体灵敏度的最高值分别提高了230％，92％，158％，49％，缩短了响应时间和恢复时间。     

溶液生长ZnO一维纳米阵列及其复合纳米结构的研究进展

对溶液生长ZnO一维纳米阵列的研究进展进行了评述,分析了晶种制备和溶液生长过程中各工艺因素对阵列微观形貌的影响,并介绍了在溶液中通过控制定点成核并利用有机基团调控ZnO晶体生长习性的合成路线用于构筑ZnO复合纳米结构的最新研究,指出了溶液生长ZnO一维纳米阵列和构筑复合结构中存在的问题及今后的研究方向.     

Effect of tin-doped indium oxide film on electrodeposition of ZnO nanostructures

Surface studies are reported for the deposition of ZnO nanostructures by one-step electrodeposition method. The electrosynthesis was perfomed at the surface of tin doped indium oxide coated glass substrates in the absence of any buffer layer. The growth of ZnO nanostructures was investigated with the morphology of substrate and the deposition mode. Combined nucleation mode was observed for the ZnO independently of substrate. The results indicated the growth, morphology and density of the ZnO nanostructures are markedly influenced by both the substrate and the deposition conditions. It was observed the ZnO formation is defect site driven in case of galvanostatic deposition mode, while in case of potentiostatic deposition mode, it is dependent on the roughness of the substrate.     

Influence of vanadium concentration on the microstructure and magnetic properties of V-doped ZnO thin films

Vanadium doped ZnO thin films (Zn_1 − xV_xO, where x = 0.05 or x = 0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.     

一维纳米氧化锌的场发射性能和光学性能研究

采用真空热蒸发法在不同的制备温度下,制备出了准阵列状和阵列状一维纳米ZnO结构。并利用X射线衍射、扫描电子显微镜、场发射测试仪、光致发光谱对ZnO纳米材料的结晶质量、形貌及场发射性能进行了分析研究。阵列状纳米氧化锌有较明显的择优生长取向。准阵列状纳米氧化锌的场发射性能优于阵列状纳米氧化锌。并通过对PL谱的对比分析得出,准阵列状纳米结构的结晶质量较好,阵列状纳米结构中存在的缺陷较多。     

Photoluminescence properties of single crystalline ZnO/CdS core/shell one-dimensional nanostructures

ZnO/CdS core/shell one-dimensional nanostructures were synthesized using ZnO nanorod arrays as templates, which were fabricated by a vapor transport process. CdS shells with various thicknesses were epitaxially grown on the ZnO nanorod arrays by metal organic chemical vapor deposition. Selected area electron diffraction measurement revealed that both ZnO cores and CdS shells were single crystalline growing along the c-axis. The photoluminescence properties of the ZnO/CdS core/shell nanostructures were also varied with different CdS shell thicknesses. A carrier transition process from ZnO to CdS was assumed to induce the enhancement of CdS photoluminescence.     

Ni掺杂对ZnO纳米线甲烷气敏性能的影响

以采用物理热蒸发法制备的纯ZnO纳米线和Ni掺杂ZnO纳米线为气敏基料，制备成旁热式气敏元件，用静态配气法对浓度为10^-4的甲烷气体进行了气敏性能的测试．结果表明Ni掺杂使ZnO纳米线对甲烷灵敏度提高了182％，响应时间和恢复时间分别缩短了3和2s．Ni的掺杂，在ZnO半导体禁带中引入新的复合中心，形成附加能级，提高了ZnO纳米线对甲烷的灵敏度．     

Fabrication of ZnO nanorods using metal nanoparticles as growth nuclei

ZnO nanorods were produced by pulsed laser deposition (PLD). Drops of nanoparticle colloid (gold or silver) were placed on silica substrates to form growth nuclei. All nanoparticles were monocrystalline, with well-defined crystal surfaces and a negative electrical charge. The ZnO nanorods were produced in an off-axis PLD configuration at oxygen pressure of 5 Pa. The growth of the nanorods started from the nanoparticles in different directions, as one nanoparticle could become a nucleus for more than one nanorod. The low substrate temperature used indicates the absence of a catalyst during the growth of the nanorods. The diameters of the fabricated 1-D ZnO nanostructures were in the range of 50-120 nm and their length was determined by the deposition time.     

Morphological control of flower-like ZnO nanostructures

Flower-like ZnO nanostructures composed of different building blocks, such as hexagonal pyramids, hexagonal prisms, and cones, have been synthesized on a large scale by a simple hydrothermal method in the absence of surfactants or organic solvents. The effects of the concentration of NaOH, reaction temperature, and reaction time on the morphologies of the resulting products have been investigated. The morphologies and the crystal structures of flower-like ZnO nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM).     

Properties of N-doped ZnO grown by DBD-PLD

N-doped ZnO thin films have been grown on sapphire substrates by dielectric barrier discharged pulsed laser deposition (DBD-PLD). Low temperature photoluminescence spectra of N-doped ZnO film verified the p-type doping status to find the acceptor-bound exciton peaks with the high resolution detection. At low temperature growth, the major defects in the N-doped ZnO film were the oxygen interstitials that can combine with N, so that the N played the role as an acceptor. On the other hand, the major defects in the samples processed at high temperature were oxygen vacancies with which N doesn't play the role as an acceptor. The acceptor binding energy of N acceptor was estimated to be about 105 meV.     

Microstructural and optical properties of Ga-doped ZnO semiconductor thin films prepared by sol-gel process

Transparent thin films of Ga-doped ZnO (GZO), with Ga dopant levels that varied from 0 to 7 at.%, were deposited onto alkali-free glass substrates by a sol-gel process. Each spin-coated film was preheated at 300 °C for 10 min, and then annealed at 500 °C for 1 h under air ambiance. The effects of Ga dopant concentrations on crystallinity levels, microstructures, optical properties, and electrical resistivities of these ZnO thin films were systematically investigated. Photoluminescence spectra of GZO thin films were examined at room temperature. XRD results revealed that the undoped ZnO thin films exhibited a preferred orientation along the (002) plane and that the ZnO thin films doped with Ga showed degraded crystallinity. Experimental results also showed that Ga doping of ZnO thin films could markedly decrease surface roughness, improve transparency in the visible range, and produce finer microstructures than those of undoped ZnO thin films. The most promising films for transparent thin film transistor (TTFT) application produced in this study, were the 3 and 5 at.% Ga-doped ZnO thin films, both of which exhibited an average transmittance of 90.6% and an RMS roughness value of about 2.0 nm.     

ZnO nanostructures grown on epitaxial GaN

Presented is the growth of zinc oxide nanorod/nanowire arrays on gallium nitride epitaxial layers. A hierarchical zinc oxide morphology comprising of different scale zinc oxide nanostructures was observed. The first tier of the surface comprised of typical zinc oxide nanorods, with most bridging to adjacent nanorods. While the second tier comprised of smaller zinc oxide nanowires approximately 30 nm in width often growing atop the aforementioned bridges. Samples were analysed via scanning electron microscopy, as well as, cross-sectional and high resolution transmission electron microscopy to elucidate the detailed growth and structural elements of the heterostructure.