Zhang Qing-yu

Vacancy Aggregation in Diamond Films grown in CH4+H2 Atmosphere by MPCVD

Transmission electron microscopy is applied to study the diamond film grown in a CH4 and H2 gaseous mixture by microwave plasma assisted chemical vapour deposition. Defects in the nanometre scale, dislocation loops, are first observed in diamond films. The dislocation loops are found to be of co-existence with planar defects and are next to the planar defects for {111} faceting grains. A possible mechanism is suggested to interpret the co-existence of dislocation loops with planar defects.

Adatom, vacancy and sputtering yields of energetic pt atoms impacting on Pt(100) by molecular dynamics simulation

We have studied the influence of incident atoms with low energy on the Pt(100) surface by molecular dynamics simulation. The interaction potential obtained by the embedded atom method (EAM) was used in the simulation. The incident energy changes from 0.1eV to 200eV and the target temperature ranges from 100 to 500 K. The target scales are 6×6×4 and 8×8×4 fcc cells for lower and higher incident energies, respectively. The adatom, sputtering, vacancy and backscattering yields are calculated. It was found that there is a sputtering threshold for the incident energy. When the incident energy is higher than the sputtering threshold, the sputtering yield increases with the increase of incident energy and the sputtering shows a symmetrical pattern. We found that the adatom and vacancy yields increase as the incident energy increases. The vacancy yields are much higher than those obtained by Monte Carlo simulation. The dependence of the adatom and sputtering yields on the incident energy and the relative atomistic mechanisms are discussed.

The mesoscopic characterization of the microhardness of superhard films of TaN, TaC and Ta(N,C)

The preparation and structure of superhard films of TaN, TaC and Ta(N,C) have been researched extensively since the 1980s because of their important properties, such as high melting point, high hardness, oxidation resistance, corrosion resistance, high chemical stability etc. [14 ] . These properties are certainly related to the material structure [5, 6]. Among these, the hardness is a measure of a materials ability to resist applied load against plastic deformation. The microhardness, Hv, can be regarded as being determined by the bonding type and strength, which are reflected in the shear modulus, and, at the same time, as being determined by the configuration parameters of crystal defects, such as the dislocation substructure and so on [7, 8]. However, the establishment of the quantitative constitution equation between the microhardness and the dislocation substructure has been attempted by many people even in dreams in the past 40 years. The objective of the study reported here was to resume this kind of effort. Of course, the dislocation substructure parameter must first be measured, then the parameters can be taken into a certain quantitative constitutive equation. The real values of microhardness are usually obtained by the indentation method, which creates some damage and plastic deformation and is influenced by the substrate. How to avoid influence from the subst, ate is a serious problem. TaN, TaC and Ta(N,C) films er coatings are generally made by the plasma vapour deposition (PVD) method. Ion beam assisted deposition (IBAD) has been used successfully to prepare superhard films of TaN, TaC and Ta(N,C) with good adhesion and homogeneity in this study. These films were deposited ente Wl8Cr4V steel and Fe (99.99%) substrates in a triode-sputtering system. Pre-vacuum varied from 1 x 10 -4 to 5 x 10 -4 torr and the pressure of argen was controlled at 1 x 10 .3 torr (1 torr = 1.333 x 102 Pa). The substrate temperature was higher than 400 °C. The deposition rate was about 9 nmmin -1. The IBAD was carried out using argen (99.99%) ions as a sputtering source, tantalum (99.99%) as target, and nitrogen (99.99%), carbon and a mixture of nitrogen and carbon as len sources. Before sputtering, the system was pumped to about 8 x 10 .6 torr. The technical parameters are listed in Table I. The thickness of the prepared thin films was about 200 nm. The measurements of microhardness Hvm were

First principles study the phase structure stability of wurtzite Zn 1 - x Mg x O alloy

The VASP (Vienna Ab-initio Simulation Package) that based on the density-functional theory (DFT) method combined with local density approximation (LDA) is used to calculate the lattice parameters, band gap, and formation enthalpy of Zn1- x Mg x O alloy taking all the doping configurations into account. The calculation results indicate that the average parameters of wurtzite ( wz ) Zn1- x Mg x O alloy, a and c , don’t follow the Vergard’s law. With increasing the Mg content, the band gap is increased and the variation of band gap can be fitted by E g=3.43+2.24 x +0.68 x 2, which is in agreement with the experimental results. The difference of E g values in different doping configurations is the main reasons to widen the photoluminescence spectra of Zn1- x Mg x O alloy. By comparing the formation enthalpy of wurtzite Zn1- x Mg x O with those of zinc blende and rocksalt Zn1- x Mg x O alloys, we find that the Zn1- x Mg x O alloy will transit from wurtzite phase into rocksalt beyond x =37.5% and wurtzite Zn1- x Mg x O phase can be coexistence with that phase of zinc blende Zn1- x Mg x O alloys at special growth condition.

Annealing behaviour of structure and morphology and its effects on the optical gain of Er3+/Yb3+ co-doped Al2O3 planar waveguide amplifier

Using transmission electron microscopy (TEM) and x-ray diffraction analysis, we have studied the structural and morphological evolution of highly Er/Yb co-doped Al2O3 films in the temperature range from 600°C–900°C. By comparison with TEM observation, the annealing behaviours of photoluminescence (PL) emission and optical loss were found to have relation to the structure and morphology. The increase of PL intensity and optical loss above 800°C might result from the crystallization of amorphous Al2O3 films. Based on the study on the structure and morphology, a rate equation propagation model of a multilevel system was used to calculate the optical gains of Er-doped Al2O3 planar waveguide amplifiers involving the variation of PL efficiency and optical loss with annealing temperature. It was found that the amplifiers had an optimized optical gain at the temperature corresponding to the minimum of optical loss, rather than at the temperature corresponding to the maximum of PL efficiency, suggesting that the optical loss is a key factor for determining the optical gain of an Er-doped Al2O3 planar waveguide amplifier.

Microstructure and photoluminescence of Er-doped SiOx films synthesized by ion beam assisted deposition

Er-doped SiOx films were synthesized at 500 degrees C by ion beam assisted deposition technique and annealed at 800 and 1100 degrees C for 2h in the air atmosphere. The analysis by using energy dispersive x-ray spectroscopy showed that the ratio of Si to O decreased from 3 in the as-deposited films to about 1 in the annealed films. The investigation by using transmission electron microscopy and x-ray diffraction indicated that annealing induces a microstructure change from amorphous to crystalline. The grain sizes in the films were about 10 and 40nm when annealed at 800 and 1100 degrees C, respectively. The films annealed at temperatures of 800 and 1100 degrees C exhibited a sharp photoluminescence (PL) at 1.533μm from the Er centres when pumped by 980nm laser. The influence of microstructure and grain size on the PL from Er-doped SiOx films has been studied and discussed.