Fabrication and photoluminescence of P doped ZnO nanobelts by thermal evaporation method

Uniform and flat single crystal ZnO:P nanobelts (NBs) were fabricated on Si (1 0 0) substrates by the thermal evaporation method. The growth process, free-catalyst self-assembly vapor-solid (V-S) mechanism, was described and investigated deeply in terms of thermodynamics and kinetics. Then, the photoluminescence (PL) properties of ZnO NBs were studied in a temperature range from 10 to 270 K. At 10 K the recombination of acceptor-bound exciton (A⁰X) was predominant in the PL spectrum, and was attributed to the transition of P_Zn−2V_Zn complex bound exciton. The active energy of A⁰X and acceptor binding energy were calculated to be 17.2 and 172 meV, respectively. The calculated acceptor binding energy of P doped ZnO nanostructure is in good agreement with that of P doped ZnO film.     

Photoluminescence of ZnO:Sb nanobelts fabricated by thermal evaporation method

Uniform ZnO nanobelts (NBs) were synthesized by a facile thermal evaporation method. Recombination mechanism of acceptor-related emissions in Sb doped ZnO NBs was investigated by temperature-dependent photoluminescence (PL) spectra. UV near-band-edge (NBE) emissions were dominant by acceptor-bound exciton (A⁰X) at 3.358 eV and free electron-to-acceptor (FA) at 3.322 eV transitions at 81 K. Studies on A⁰X intensity showed a quenching channel, the thermal dissociations of A⁰X to a free exciton and electron hole pair with the temperature increase. The active energy of A⁰X was estimated to be 19 meV using thermal quenching formula. The acceptor ionization energy was calculated to be 190 meV using Haynes rule. These results were very similar to those of antimony or phosphorus doped ZnO films.     

Microstructure and optical properties of ZnO nanoparticles prepared by a simple method

In this investigation, ZnO nanoparticles were prepared by a simple and rapid method. This method is based on the short time solid state milling and calcinations of zinc acetate and citric acid powders. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, photoluminescence and UV-vis spectroscopy. It was shown that the calcination temperature significantly affected the particle size and optical properties of the synthesized ZnO nanoparticles. Calculation based on the XRD data shows that the average sizes of ZnO particles are in agreement with those from TEM images and the size of the particles increases on increasing the calcination temperature. Also the band gap of samples decreased from 3.29 to 3.23 eV on increasing the calcination temperature from 350 to 600 °C. Photoluminescence analyses show that many defects such as interstitial zinc, zinc vacancy and oxygen vacancy are responsible for the observed optical properties.     

One-dimensional and quasi-one-dimensional ZnO nanostructures prepared by spray-pyrolysis-assisted thermal evaporation

One-dimensional (1D) and quasi-1D ZnO nanostructures have been fabricated by a kind of new spray-pyrolysis-assisted thermal evaporation method. Pure ZnO powder serves as an evaporation source. Thus-obtained products have been characterized by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM). The room temperature photoluminescence spectrum of these ZnO nanostructures is presented. The results show that as-grown ZnO nanomaterials have a hexagonal wurtzite crystalline structure. Besides nanosaws, nanobelts and nanowires, complex ZnO nanotrees have also been observed in synthesized products. The study provides a new simple route to construct 1D and quasi-1D ZnO nanomaterials, which can probably be extended to fabricate other oxide nanomaterials with high melting point and doped oxide nanomaterials.     

Fabrication and characterization of ZnO micro and nanostructures prepared by thermal evaporation

A simple method of thermal evaporation to fabricate micro and nanostructures of zinc oxide was presented. ZnO micro and nanostructures, prepared under different quantity of O₂, were characterized by techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and analytical transmission electron Microscope. The SEM images indicated that the products prepared under the condition of sufficient O₂ were needle-like microrods and the samples synthesized under the condition of deficient O₂ were nanorods and nanowires with very high aspect ratio. The results of XRD and Raman shifts revealed that the ZnO micro and nanostructures synthesized under different quantity of O₂ were both single crystalline with the hexagonal wurtzite structure. The HRTEM images indicated that the ZnO nanowire prepared under the condition of deficient O₂ was single crystalline and grown along the direction of [0 0 1]. Photoluminescence measurement was carried out and it showed that the spectra of ZnO micro and nanostructures prepared under different quantity of O₂ exhibited similar emission features. In addition, the growth mechanism of ZnO micro and nanostructures was preliminarily discussed.     

Strong visible photoluminescence in amorphous SiOx and SiOx : H thin films prepared by thermal evaporation of SiO powder

Amorphous SiO_x and SiO_x : H films were prepared by thermal evaporation of SiO powder in ultrahigh vacuum or under a flow of hydrogen ions onto silicon substrates maintained at 100°C. Photoluminescence (PL) can be seen in the visible range with the naked eye on the as-deposited samples without post-treatments. Composition and structure investigations were performed by infrared and Raman spectrometry experiments on films annealed at different temperatures. Hydrogen and oxygen bonding was studied by infrared spectrometry. The PL is attributed to the quantum confinement of excitons in a-Si clusters embedded in the a-SiO_x matrix. Our results demonstrate that oxygen creates an efficient potential barrier and no further passivation by hydrogen is necessary.     

Growth and properties of ZnO nanorod and nanonails by thermal evaporation

ZnO nanorods and nanonails have been synthesized on silicon wafers by a three-step catalyst-free thermal evaporation method in oxygen atmosphere. All the samples were hexagonal phase ZnO with highly c-axis preferential orientation. Different morphologies of ZnO nanostructures, i.e. ZnO nanorods and two kinds of nanonails, were observed at various temperature regions. Photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscope were employed to elucidate the reason for the formation of such different rod-like structures. The analysis results demonstrated that the caps of nanonails possess a large number of oxygen vacancies, which may play a key role in determining the formation of nanonails and the high intensity of green emission.     

Optical properties of rubrene thin film prepared by thermal evaporation

Rubrene thin films are deposited on quartz substrates and silver nanoparticles(Ag NPs) films by the thermal evaporation technique. The optical properties of rubrene thin film are investigated in a spectral range of 190 nm–1600 nm. The analysis of the absorption coefficient(α) reveals direct allowed transition with a corresponding energy of 2.24 e V. The photoluminescence(PL) peak of the rubrene thin film is observed to be at 563 nm(2.21 e V). With the use of Ag NPs which are fabricated by radio-frequency(RF) magnetron sputtering on the quartz, the PL intensity is 8.5 times that of as-deposited rubrene thin film. It is attributed to the fact that the surface plasmon enhances the photoluminescence.     

Trench-template fabrication of indium and silicon nanowires prepared by thermal evaporation process

In this study, we report on the trench-template assisted fabrication of nanowires for thermally evaporated indium and silicon thin films on quartz substrate. Length of the nanowires is completely dependent on the length of the trench, whereas the diameter of the nanowires is dependent on the thickness of the thin film. The diameter of nanowire increases from 200 nm to 1 μm when the thickness was increased from 15 to 60 nm. It is observed that nanowires diameter is invariably controlled by material deposition thickness. Average crystallite sizes for 60 nm indium and silicon deposition inside the trench are 120 and 35 nm, respectively. Nanowire surface plasmon peak shift as compared to the same thickness untemplated continuous thin film is more for thinner nanowires. This technique of nanowire fabrication is shown to be versatile in nature.     

Synthesis and optical properties of flower-like ZnO nanorods by thermal evaporation method

Flower-like ZnO nanorods have been synthesized by heating a mixture of ZnO/graphite powders using the thermal evaporation and vapor transport on Si (1 0 0) substrates without any catalyst. The structures, morphologies and optical properties of the products were characterized in detail by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman spectroscopy. The synthesized products consisted of large quantities of flower-like ZnO nanostructures in the form of uniform nanorods. The flower-like ZnO nanorods had high purity and well crystallized wurtzite structure, whose high crystalline quality was proved by Raman spectroscopy. The as-synthesized flower-like ZnO nanorods showed a strong ultraviolet emission at 386 nm and a weak and broad yellow-green emission in visible spectrum in its room temperature photoluminescence (PL) spectrum. In addition, the growth mechanism of the flower-like ZnO nanorods was discussed based on the reaction conditions.     

Gas sensing properties of zinc oxide nanostructures prepared by thermal evaporation

Progress has been achieved in the synthesis, structural characterization and physical properties investigation of nanostructures. We have focused our attention on zinc oxide nanostructures. We report on the growth of ZnO nanostructures using vapour phase technique. We have synthesized, depending on the growth conditions, different nanostructures such as wires and combs of zinc oxide. ZnO nanowires electrical properties have been characterised in presence of different gases, the results highlight remarkable response to acetone and ethanol with detection limits lower than 1 ppm. PACS 73.63.Bd; 74.78.Na     

Annealing effect on the morphologies and photoluminescence properties of ZnO nanocombs

In order to examine the annealing effect on morphologies and photoluminescence properties of the as-synthesized ZnO nanocombs, they were annealed in argon and in air at 800 °C for 10 h, respectively. The SEM, TEM, HRTEM, and PL examination results show that the morphologies and photoluminescence properties of ZnO nanocombs annealed in argon are quite different from those of ZnO nanocombs annealed in air. To anneal ZnO nanocombs in air caused the disappearance of combs, the enhancement of ultraviolet emissions, and the disappearance of emissions in the visible spectral region. On the other hand, the combs still existed, and the green emission centering at 500 nm still existed after annealing ZnO nanocombs in argon. The mechanisms for the morphological and photoluminescence evolution of annealed ZnO nanocombs are also proposed.     

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg     

The structure and magnetic properties of Cu-doped ZnO prepared by sol-gel method

The Cu-doped ZnO and pure ZnO powders were synthesized by sol-gel method. The structural properties of the samples were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. All the results confirmed that copper ions were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO nanoparticles. The Zn_0.97Cu_0.03O nanoparticles exhibited ferromagnetism at room temperature, as established by the vibrating sample magnetometer analysis.     

氧化锌/硅纳米孔柱阵列的结构和光致发光特性研究

以硅纳米孔柱阵列(Si-NPA)为衬底、用化学气相沉积法制备了具有规则阵列结构特征的ZnO/Si-NPA纳米复合体系，并对其结构和光致发光性质进行了表征. 实验结果显示，组成ZnO/Si-NPA表面阵列的每个柱子均呈现层壳结构. 不同于衬底Si-NPA的红光和蓝光发射，ZnO/Si-NPA在紫外光区和蓝绿光区呈现出两个强的宽发光峰. 分析表明，紫外光发射应归因于ZnO晶体的带边激子跃迁；而蓝绿光发射则来自于ZnO晶体本征缺陷所形成的两类深能级复合中心上载流子的辐射跃迁.     

Synthesis and optical properties of nanocrystalline ZnO powders prepared by a direct thermal decomposition route

This paper reports the synthesis and optical properties of nanocrystalline ZnO powders with crystallite sizes of 32.5 (±1.4)–43.4 (±0.4) nm prepared by a direct thermal decomposition of zinc acetate at the temperatures of 400, 500, 600, and 700°C for 4 h. The structure of the prepared samples was studied by XRD and FTIR spectroscopy, confirming the formation of wurtzite structure. The morphology of the samples revealed by SEM was affected by the thermal decomposition temperature, causing the formations of both nanoparticles and nanorods with different size and shape in the samples. The synthesized powders exhibited the UV absorption below 400 nm (3.10 eV) with a well defined absorption peak at around 285 nm (4.35 eV). The estimated direct bandgaps were obtained to be 3.19, 3.16, 3.14, and 3.13 eV for the ZnO samples thermally decomposed at 400, 500, 600, and 700°C, respectively. All the samples exhibited room-temperature photoluminescence (PL) showing a strong UV emission band at ∼395 nm (3.14 eV), a weak blue band at ∼420 nm (2.95 eV), a blue–green band at ∼485 nm (2.56 eV), and a very weak green band at ∼529 nm (2.35 eV). The mechanisms responsible for photoluminescence of the samples are discussed.     

热沉积法制备纳米二硫化钼薄膜及其光电特性研究

以M oS2粉末为原料,以氩气为携载气体,在400～600℃温度范围内利用热蒸发方法在硅衬底表面制备了不同厚度的M oS2薄膜．利用X射线衍射和扫描电子显微镜分析了M oS2薄膜的结构和表面形貌,发现M oS2薄膜由多晶M oS2粒子组成,颗粒均匀,平均纳米颗粒尺寸约为60 nm ．利用紫外可见光光谱仪测量了其吸收特性,发现样品在720 nm附近有很强的吸收．应用霍尔效应和伏安法研究了M oS2/Si样品的接触特性和电子的运输特性,发现该异质结具有良好的整流特性,即正向电压下电流随电压呈指数增长,而在反向偏压下漏电流很小,电子迁移率可达到6．730×102 cm2/（V · s）．实验结果表明MoS2薄膜具有良好的电学特性,可用来制备晶体管和集成电路等器件．     

Study of the microstructural and photoluminescence properties of Li-doped ZnO thin films prepared by spray pyrolysis

Lithium-doped zinc oxide films were synthesized by spray pyrolysis technique, and their structural and optical properties were characterized by X-ray diffraction, transmission electron microscope, atomic force microscope, and photoluminescence spectroscopy. The effect of doping on the photoluminescence properties was investigated at room temperature (300 K). Polycrystalline nature of the films was confirmed from X-ray diffraction and electron microscopic studies. A two-dimensional fringe moiré pattern with spacing of 1.2 nm was observed for the doped thin film. Lithium doping has been found to increase the roughness of the surface, thus making the film more passivated. Lithium was found to play a key role in the excitonic as well as visible luminescence of ZnO.     

The effects of activated carbon supports on the structure and properties of TiO2 nanoparticles prepared by a sol-gel method

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.     

Structural and photoluminescence characteristics of ZnO films by room temperature sputtering and rapid thermal annealing process

ZnO thin films deposited on SiO₂/Si substrates at room temperature by sputtering technology were annealed with a rapid thermal annealing process at various temperatures from 200 °C to 900 °C. The physical and optical properties of the ZnO films were investigated by X-ray diffraction, scanning electron microscopy and room-temperature photoluminescence (PL). The surface structures of the thin films showed great variations with increased annealing temperature. The PL spectrum illustrated that a stronger UV emission intensity appeared at an annealing temperature of 500 °C. On the other hand, visible-light emission could be obtained when the ZnO films were annealed above 500 °C and reached a maximum intensity at 900 °C. The possible mechanisms for visible-light emission are discussed. PACS 81.15.Cd; 81.40.Ef; 78.55.-m; 78.55.Et