Li Jin-chai

Synthesis of Zinc Oxide Hollow Spherical Structure via Precursor-Template and Formation Mechanism

We report the realization of uniform zinc oxide (ZnO) hollow spherical structure consisting of highly radial and oriented ZnO nanorods, which results from a facile precursor-templated synthesis through thermal evaporation at a relative low temperature without any catalyst. By optimizing the experimental parameters, the obtained results demonstrate that the morphology of ZnO is very sensitive to Zn powder precursor. Detailed structural analyses confirm that this microstructure exhibits a wurtzite hexagonal phase and those nanorods are preferentially oriented along the c -axis direction. The formation mechanism of the microstructure is proposed to be a vapor–solid process. This method may provide a simple and versatile approach to large-scale production of hollow spherical ZnO structure.

The preparation and characterization of amorphous SiCN thin films

Radio Frequency plasma enhanced Chemical Vapor Deposition (RF CVD) using N2, SiH4 and C2H4 as the reaction sources was used to prepare amorphous ternary SixCyNz thin films. The chemical states of the C, Si and N atoms in the films were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR). The refractive indexn, extinction coefficientk and optical band gapEopt of the thin films were investigated by UV-visible spectrophotometer and spectroscopic ellipsometer. The results show that a complex chemical bonding network rather than a simple mixture of Si3N4, SiC, CNx and a-C etc., may exist in the ternary thin films. Thens of the films are within the range of 1. 90–2. 45, andEopts of all samples are within the range of 2. 71–2. 86 eV.

Electron Field Emission of CNx Thin Films Prepared by Low Pressure Plasma Enhanced Chemical Vapour Deposition

CNx thin films were prepared using low pressure plasma enhanced chemical vapour deposition, and then bombarded by low-energy N2+. The compositions before and after N2+ bombardment were compared using x-ray photoelectron spectroscopy. The electron field emission characteristics of CNx thin films before and after N2+ bombardment were studied under the pressure of 10-6 Pa. For the samples, the turn-on emission field decreased from 2.5 V/µm to 1.2 V/µm while the stable current density increased from 0.5 mA/cm2 to a value larger than 1 mA/cm2 before and after the bombardment. Our results illustrate that the field emission characteristics were improved after the bombardment of N+2.

Synthesis, Characterization and Photoluminescence of Well-Ordered ZnO Micropillars Grown on ZnO Buffer Layers

Using ZnO buffer layers prepared by simply thermal oxidation of ion beam sputtered Zn films, highly oriented and uniformly aligned single-crystalline ZnO micropillars arrays have been synthesized by thermal evaporation of Zn powder with free catalysts at low temperature of 430 °C. The ZnO micropillars show sharp hexagonal umbrella-like tips with thin ZnO nanowire grown on the tips. The umbrella-like tips grow in a layer-by-layer mode along the direction of [001]. The growth mechanism has been discussed. The formation of the micropillars basically depends on the gradually decreasing Zn vapor pressure and subsequently cooling process. The photoluminescence (PL) spectrum indicates a moderately good crystal quality of the ZnO micropillars. Our results may reinforce the understanding of the formation mechanism of different ZnO nano/microstructures. This kind of complex microstructures may find potential applications in multifunctional microdevices, optoelectronic and field emission devices.

Low-energy H2+ implantation effects on the characteristics of polysilicon solar cells

Low-energy H2+ ions were implanted into polysilicon solar cells to passivate the electrically active centers which existed in grains and grain boundaries. The illuminative and dark characteristics of solar cells were significantly improved. Measurements of the optical properties of monosilicon samples showed that the refractive index n was decreased after H2+ bombardment, and the value of the optical band gap Eg was increased from 1.1 eV of monosilicon to 1.3 eV. A thermal stability test was performed after hydrogenation. The refractive index n of hydrogenated samples rose again after annealing above 300°C, but the absorption coefficient α did not change significantly, even after annealing at 900°C for 30 min.

Synthesis and optical property study on ZnO nanostructures via vapor phase growth

Nanostructural zinc oxide films have been synthesized via vapor phase growth by heating pure zinc powder. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) results showed that four kinds of morphologies ZnO nanostructures namely nanowires, well-aligned nanorods, nanofeathers and hexagonal nanorods were formed and all of wurtzite structural crystals. The results indicated that the temperature and substrate play an important role in the formation of different morphologies of ZnO nanostructures. The photoluminescence (PL) measurement was carried out for the well-aligned nanorods ZnO sample and blue emission peaks at 420 and 444 nm have been observed at room temperature. And the blue emission mechanism is discussed.

Field emission characterization of 1D-nanostructural ZnO grown at low temperature

By heating pure zinc powder at low temperature, two kinds of ZnO nanostructures with different morphology and diameter were grown on silicon (1 0 0) substrates. Scanning electron microscopy images show that ZnO nanorods and ZnO nanowires have been obtained. XRD demonstrates that the grown ZnO nanostructures are hexagonal wurtzite crystalline. The electron field emission properties were studied for both kinds of samples. The ZnO nanorods sample has a low turn-on field at 3.6 V/μm owing to better alignment, while the field to obtain a current density of 1 mA·cm2 is higher (at 11. 2 V/μm) than that of the nanowires sample due to bigger diameter. For nanowires sample, an emission current of 1·mA·cm2 is achieved at 8.2 V/μm which is lower than that of ZnO nanorods owing to better high aspect ratio.

Field emission of SiCN thin films bombarded by Ar+ ions

SiCN thin films were synthesized by a radio frequency chemical vapor deposition (RFCVD) system on P-type Si (1 0 0) wafers using C2H4, SiH4 and N2 as raw materials, In order to get rid of the oxygen absorbed on the surface and improve the characteristics of electron field emission, Ar+ ions of low energy were used to bombard the samples. The field emission characteristics of SiCN thin films before and after Ar+ bombardment were studied in the super vacuum environment of 10−6 Pa. It was showed that the turn-on field (defined as the point where the current-voltage curve shows a sharp increase in the current density) decreased from 38 V/μm before bombardment to 25 V/μm after bombardment. And the maximum emission current density increased from 159.2 to 267.4 μA/cm2. The composition before and after Ar+ bombardment was compared using X-ray photoelectron spectroscopy (XPS). Our results illustrated that the field emission characteristics were improved after the bombardment of Ar+.

Studies on Wear and Corrosion Resistances of Carbon Nitride Thin Films on Ti Alloy

CNx/SiCN composite films were prepared on titanium (Ti) alloy substrates by Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD). As a buffer layer, SiCN ensured the adhesion of the CNx thin films on Ti substrates. X-ray diffraction (XRD) measurement revealed that the composite films possessed α-C3N4 structure. The microhardness of the films was 48 to 50 GPa. In order to test the characteristics of wear and corrosion resistances, we prepared Ti alloy samples with and without CNx/SiCN composite films. Also for strengthening the effect of wear and corrosion, the wear tests were carried out under high load (12 MPa) and in 0.9% NaCl solution. Results of the wear tests and the corrosive electrochemical measurements showed that the samples coated with CNx films had excellent characteristics of wear and corrosion resistances compared with Ti alloy substrate samples.

Silicon field emission arrays coated with CNx thin films

Arrays of silicon micro-tips were made by etching the p-type (1 0 0) silicon wafers which had SiO2 masks with alkaline solution. The density of the micro-tips is 2×104 cm−2. The Scanning Electron Microscope (SEM) photos showed that the tips in these arrays are uniform and orderly. The CNx thin film, with the thickness of 1.27 μm was deposited on the silicon micro-tip arrays by using the middle frequency magnetron sputtering technology. The SEM photos showed that the films on the tips are smoothly without particles. Keeping the sharpness of the tips will benefit the properties of field emission. The X-ray photoelectron spectrum (XPS) showed that carbon, nitrogen and oxygen are the three major elements in the surfaces of the films. The percents of them are C: 69.5%, N: 12.6% and O: 17.9%. The silicon arrays coated with CNx thin films had shown a good field emission characterization. The emission current intensity reached 3.2 mA/cm2 at 32.8 V/μm, so it can be put into use. The result showed that the silicon arrays coated with CNx thin films are likely to be good field emission cathode. The preparation and the characterization of the samples were discussed in detail.