ZnO nanoparticles obtained by mechanochemical technique and the optical properties

Crystalline ZnO nanoparticles were synthesized by mechanochemical method. Mechanochemical processing involves the mechanical activation of solid-state displacement reactions at low temperatures in a ball mill. Statistical design was used to investigate the effect of main parameters (i.e. time, milling rate and calcination temperature) on ZnO crystallite size and morphology. After annealing at 400 °C in air, zinc oxide (ZnO) nanoparticles were obtained. The milled powders are analyzed by X-ray diffraction (XRD), TG/DTA and transmission electron microscope (TEM).The crystallite size of ZnO samples calculated from XRD is consistent with the TEM images and estimated to be less than 20 nm. The optical properties of the samples were studied by UV-vis spectrophotometer.     

Photoluminescence observations of hydrogen incorporation and outdiffusion in ZnO thin films

ZnO thin films were deposited with the addition of H₂ to the reaction gas using the atmospheric-pressure metal organic chemical vapor deposition method. The incorporation and outdiffusion of hydrogen in ZnO films were investigated by comparing the intensity of the hydrogen-related bound-exciton peak (I₄: 3.363 eV) in the photoluminescence spectrum. The intensity of I₄ peak was found to be the strongest in the ZnO film deposited at 680 °C with H₂ present. However, for the ZnO films prepared at the same temperature 680 °C but without H₂ present and at the higher temperature of 900 °C with H₂ present, respectively, the I₄ peak was just a minor shoulder of another bound-exciton peak (I₈: 3.359 eV). The intensity of I₄ peak in the ZnO films deposited with H₂ present was found to decrease with the increasing of annealing temperature. These results suggest that it is difficult for hydrogen to incorporate into ZnO thin films grown at high temperatures even in the hydrogen-present ambient.     

Low-temperature synthesis of ZnO nanonails

Wurtzite ZnO nanonails on silicon substrate were successfully synthesized by thermal vapor transport and condensation method at a low temperature without a metal catalyst. Pure Zn powders were used as raw material and O₂/Ar powders as source gas. The products were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the deposited nanostructures include aligned ZnO nanonails. The ZnO nanonails, with crystalline cap and small-diameter shafts, grow along the c-axis. The optical properties have been revealed by photoluminescence spectra. We considered that the ZnO nanonails growth is a vapor-solid process.     

Growth temperature dependent evolutions of microstructural, optical and magnetic properties of Zn0.75Co0.25O films

Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence （PL）, field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy （XPS）. It is shown that Zn0.75Co0.25O films grown at low temperatures （250-350℃） are of single-phase wurtzite structure. Films synthesized at 300 or 350℃ reveal room temperature （RT） ferromagnetism （FM）, while su for 250℃ fabricated films is found above 56 K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250℃ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.     

Ultraviolet detectors based on ZnO films by thermal oxidation of Zn metallic films

Metallic Zn films were deposited on glass substrates by electron-beam evaporation. ZnO films were synthesized by thermal oxidation of Zn metallic films in air. At the annealing temperature of 550 °C, ZnO nanowires appeared on the surface, which mainly result from the decrease of oxidation rate. A ZnO ultraviolet photodetector was fabricated based on a metal-semiconductor-metal planar structure. The detector showed a large UV photoresponse with an increase of two orders of magnitude. It is concluded that promising UV detectors can be obtained on ZnO films by thermal oxidation of Zn metallic films. The ways of performing spectral response measurements for polycrystalline ZnO films are also discussed.      

Mn掺杂ZnO光学特性的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法计算了纤锌矿ZnO及不同量Mn 掺杂ZnO 晶体的电子结构，分析了掺杂对ZnO 晶体的能带结构、电子态密度、差分电荷分布的影响. 计算结果表明，随着Mn 掺杂含量的增加，ZnO 禁带宽度相应增加并且对紫外吸收区的光吸收能力也随之增强.     

NH3气氛处理制备p型ZnO薄膜及性能表征

采用NH₃气氛处理直流/射频共溅射方法制得的ZnO：Al薄膜，从而获得Al+N共掺p型ZnO薄膜.XRD，场发射扫描电子显微镜测试及Hall效应测试发现，处理温度对ZnO薄膜的结构和电学性能具有较大的影响，其中处理温度为700℃时，薄膜具有较好的c轴择优取向，并且薄膜表面平整，结构紧密，晶粒大小均匀，无明显空洞和裂缝，具有良好的表面质量，晶粒尺寸约为40—60nm，薄膜的导电类型由n型转变为p型.     

Evolution of ZnO nanostructures by non-catalytic growth process on steel alloy substrate: Structural and optical properties

Various kind of ZnO nanostructures such as nanowires, nanonails and nanocombs were synthesized by the thermal evaporation process onto the steel alloy substrate without the use of metal catalyst or any additives. Detailed structural characterizations indicated that the grown products possess a single crystallinity with the wurtzite hexagonal crystal structure. Presence of strong optical-phonon E₂ mode, in all the cases, presents the good crystallinity with the wurtzite hexagonal phase for the deposited products. Additionally, appearance of dominated, strong and sharp UV emission in the room-temperature photoluminescence spectra confirmed the good optical properties for the grown nanostructures. A vapor–solid growth mechanism has been proposed for the growth of the nanostructures.     

Preparation of ZnO–Al2O3 Particles in a Premixed Flame

Zinc oxide (ZnO) and alumina (Al₂O₃) particles are synthesized by the combustion of their volatilized acetylacetonate precursors in a premixed air–methane flame reactor. The particles are characterized by XRD, transmission electron microscopy, scanning mobility particle sizing and by measurement of the BET specific surface area. Pure (-)alumina particles appear as dendritic aggregates with average mobile diameter 43–93 nm consisting of partly sintered, crystalline primary particles with diameter 7.1–8.8 nm and specific surface area 184–229 m²/g. Pure zinc oxide yields compact, crystalline particles with diameter 25–40 nm and specific surface area 27–43 m²/g. The crystallite size for both oxides, estimated from the XRD line broadening, is comparable to or slightly smaller than the primary particle diameter. The specific surface area increases and the primary particle size decreases with a decreasing flame temperature and a decreasing precursor vapour pressure. The combustion of precursor mixtures leads to composite particles consisting of zinc aluminate ZnAl₂O₄ intermixed with either ZnO or Al₂O₃ phases. The zinc aluminate particles are dendritic aggregates, resembling the alumina particles, and are evidently synthesized to the full extent allowed by the overall precursor composition. The addition of even small amounts of alumina to ZnO increases the specific surface area of the composites significantly, for example, zinc aluminate particles increases to approximately 150 m²/g. The gas-to-particle conversion is initiated by the fast nucleation of Al₂O₃ or ZnAl₂O₃, succeeded by a more gradual condensation of the excess ZnO with a rate probably controlled by the cooling rate for the flame.     

ZnO: Cu,Sn electroluminescent phosphor

The a.c. electroluminescent characteristics of ZnO:Cu, Sn powder phosphor have been investigated in audio frequency range. A simple preparative method for this phosphor has been described. The detailed variation of light output during one cycle of the applied sinusoidal voltage has been studied and discussed. In addition to the two primary peaks, the two secondary peaks have also been observed in each cycle of the applied field. The voltage and frequency dependence of the time-averaged electroluminescent brightness have been found to follow the Alfrey-Taylor relation over a wide range of frequencies. The constants of this relation have been determined. The spectral energy distribution of this phosphor shows that the peak-shift depends upon the a.c. frequency and is independent of the magnitude of applied field.