Wu Wei-Dong

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temperature. The as-deposited films are annealed at different temperatures from 400 ?C to 800 ?C in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400 ?C to 800 ?C. The band gap of the as-deposited ZnO:In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400 ?C. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400 ?C to 800 ?C.

A Potential Hydrogen-Storage Media: C2H4 and C5H5 Molecules Doped with Rare Earth Atoms

Using first-principles calculations, we predict that a single C2H4 or C5H5 molecule can form a stable complex with two rare earth metals such as La, Eu, and Ho. The La2C2H4 complex then absorbs up to sixteen hydrogen molecules, reaching a gravimetric storage capacity of 9.5wt% by adding a rare-earth metal atom, The results show that Eu-4f electrons have little impact on the hydrogen adsorption. The nature of bonding between Eu and H2 is due to the hybridization of Eu-5d with the H-1s orbital.

Simulation of Light Intensification Induced by Defects of Polished Fused Silica

Light intensity distribution in the vicinity of inclusions and etched cracks in polished fused silica at wavelength scale are simulated by using the finite-difference time-domain algorithm. Light intensity enhancement factor as functions of diameter and refractive index of inclusions are investigated, more than 10 times that of incident beam is obtained in the simulation. We model the etched crack in close proximity to a real structure, which is characterized by AFM. We find that the peak light intensity of the crack is a function of its cross sectional breadth depth ratio, providing good hints for the effective processing of fused silica samples to improve the damage threshold.

Sputtering pressure influence on growth morphology, surface roughness, and electrical resistivity for strong anisotropy beryllium film

The strong anisotropy beryllium (Be) films are fabricated at different sputtering pressures by direct current magnetron sputtering. With the increase of pressure, the deposition rate of Be film first increases, and when the pressure exceeds 0.8 Pa, it gradually descends. The X-ray diffraction analysis indicates that Be film is of α-Be phase, its surface always reveals the (101) crystal plane possessing the low surface energy. As for the growth morphology of Be film, the surface is mainly characterized by the fibrous grains, while the cross section shows a transition from a columnar grain to a mixed grain consisting of a cone-shaped grain and a columnar grain as the sputtering pressure increases. The large grain fraction decays exponentially from 75.0% to 59.3% with the increase of sputtering pressure p, which can improve the grain size uniformity. The surface roughness increases due to the insufficient atom diffusion, which is comparable to its decrease due to the etching effect at p 0.8 Pa, and this increase is dominated by the atom diffusion. The electrical resistivity values of Be films range from 1.7 μΩm to 2.7 μΩm in the range 0.4 Pa–1.2 Pa, which is 50 times larger than the bulk resistivity.

Electronic and optical properties of Au-doped Cu2O: A first principles investigation

The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of the band gap, and the additional absorption, are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the more important factors influencing the photovoltaic activity of Cu2O film.

Measurement of ZnO/Al2O3 Heterojunction Band Offsets by in situ X-Ray Photoelectron Spectroscopy

ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy. The band offsets of the ZnO/Al2O3 heterojunction are studied by in situ x-ray photoelectron spectroscopy. The valence band of Al2O3 is found to be 3.59±0.05eV below that of ZnO. Together with the resulting conduction band offset of 2.04±0.05eV, this indicates that a type-I staggered band line exists at the ZnO/Al2O3 heterojunction.

Ion-implanted Mechanism of the Deposition Process for Diamond-Like Carbon Films

Due to the local densification, high-energy C and doped ions can greatly affect the bonding configurations of diamond-like carbon films. We investigate the corresponding affection of different incident ions with energy from 10 eV to 600 eV by Monte Carlo methods. The ion-implanted mechanism called the subplantation (for C, N, O, W, Y, etc.) is confirmed. Obvious thermal effect could be induced by the subplantation of the incident ions. Further, the subplantation of C ions is proved by in situ reflection high energy electron diffraction (RHEED). The observation from an atomic force microscope (AFM) indicates that the initial implantation of C ions might result in the final primitive-cell-like morphology of the smooth film (in an area of 1.2 mm × 0.9 mm, rms roughness smaller than 20 nm by Wyko).

Optical Properties of Co-BaTiO3/Mg(100) Nano-Composite Films Grown by Pulsed Laser Deposition Method

Co nanoparticles embedded in a BaTiO3 matrix, namely Co-BaTiO3 nano-composite films are grown on Mg(100) single crystal substrates by the pulsed laser deposition (PLD) method at 650°C. Optical properties of the Co- BaTiO3 nano-composite films are examined by absorption spectra (AS) and photoluminescence (PL) spectra. The results indicate that the concentration of Co nano-particles strongly influences the electron transition of the Co-BaTiO3 nano-composite films. The PL emission band ranging from 1.9 to 2.2 eV is reported. The AS and PL spectra suggest that the band gap is in the range of 3.28-3.7 eV.

Enhancement of the Number of Fast Electrons Generated in a Laser Inverse Cone Interaction

Enhancement of the energy-conversion efficiency from laser to target electrons is demonstrated by two-dimensional particle-in-cell simulations in a laser-inverse cone interaction. When an intense short-pulse laser illuminates the inverse cone target, the electrons at the cone end are accelerated by the ponderomotive force. Then these electrons are guided and confined to transport along the inverse cone walls by the induced electromagnetic fields. A device consisting of inverse hollow-cone and multihole array plasma is proposed in order to increase the energy-conversion efficiency from laser to electrons. Particle-in-cell simulations present that the multiholes transpiercing the cone end help to enhance the number of fast electrons and the maximum electron energy significantly.

Hydrogen storage in BC 3 composite single-walled nanotube: a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory (DFT) and grand canonical Monte Carlo simulations (GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes. Furthermore, the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions. The present results have shown that with both computational methods, the hydrogen storage capacity of BC3 nanotubes is superior to that of carbon nanotubes. The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.