Ye Ming-sheng

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.

Plasma Enhanced Chemical Vapor Deposition Synthesizing Carbon Nitride Hard Thin Films

Using plasma enhanced chemical vapor deposition and SiC and carbon buffer layers, we have obtained carbon nitride thin films on Si(100) and Si(111). The x-ray diffraction and x-ray photoelectron spectroscopy are used to characterize the thin films. The Vickers hardness of the carbon nitride thin films is more than 5100 kgf/mm2 and comparable to that of diamond.

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.

Low Energy H + Effects on the Photovoltaic and Optical Properties of Polycrystalline Silicon Solar Cells

Low energy hydrogen ion was used to passivate the electrically active defects existing in grains and grain boundaries of polycrystalline silicon solar cells. Short-circuit current of H+ implanted cells remarkably increased before and after preparing TiO2AR (antireflective) coating. The measurements (at λ=6328 Å) of the optical properties of H+ implanted silicon samples show that: the value of absorption coefficient reached the level of a-Si; refractive indexn and refłectivityR significantly decreased; the optical band gap increased from 1.1 eV to 1.3 eV. The results indicate that Si-H bonds have been formed after H+ implantation. The calculation shows that the optical thickness cycle of TiO2 AR coating will reduce correspondingly in order to obtain the optimum optical match between AR coating and implanted silicon since refractive index decreases after H+ implantation.

PREPARATION OF GAN THIN FILMS BY REACTIVE IONIZED CLUSTER BEAM TECHNIQUE

GaN thin films were prepared by reactive ionized cluster beam technique at relatively low substrate temperature about 400°C. The composition, structure and morphology of the films were characterized by x-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The binding energy of N 1s electron in the film is 397.85 eV which shows the formation of Ga-N bonding. The film has a polycrystalline structure revealed by the measurement results of TEM and SEM. It was found that raising nitrogen ion ratio in the beam is helpful to decrease oxygen content in the film.