Papers by Author: Li Ping Feng

Abstract: We investigate and simulate the permeation behavior of PET membranes on which thin coatings are deposited. Depending on the parameters of deposition and on the thin coating thickness, we assume this alteration could make it possible to decrease by one order of magnitude the permeation coefficient. Some specific developments have been necessary, all the more not only a decrease of permeation is expected but also the mechanical strength of the thin coating during severe mechanical loadings. We consequently design devices dedicated to the permeation test but also to the bulge and blister tests which permit to check the mechanical properties of the film and its adhesion on the PET surface. This paper focuses on the permeation test.

Abstract: The electronic properties of N-doped orthorhombic SrHfO₃ have been calculated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory with the local density approximation. From the calculated band structure and density of states, the bandgap reduction is observed due to the presence of the N-2p states in the top of valence bands, which leads to red-shift. Moreover, in order to clarify the charge transfer and bonding properties of N-doped orthorhombic SrHfO₃, we have calculated and analysed the charge density.

Abstract: Electronic structure, effective masses and optical properties of monoclinic HfO₂ were studied using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated equilibrium lattice parameters are in agreement with the previous works. From the band structure, the effective masses and optical properties are obtained. The calculated band structure shows that monoclinic HfO₂ has indirect band gap and all of the effective masses of electrons and holes are less than that of a free electron. The peaks position distributions of imaginary parts of the complex dielectric function have been explained according to the theory of crystal-field and molecular-orbital bonding.

Abstract: Structural, electronic and optical properties of 2H-CuAlO₂ were computed, using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The equilibrium lattice parameters, band structure, densities of states (DOS) and charge densities of 2H-CuAlO₂ have been obtained. The equilibrium lattice parameters, band structure and DOS are found to be in good agreement with the available experimental and calculational values. The charge densities and the chemical bonding of 2H-CuAlO₂ are analyzed, which show that bonding between Cu and O is mainly covalent due to Cu 3d and O 2p hybridization and that bonding between Al and O is mainly ionic. The complex dielectric function, refractive index and absorption coefficient of 2H-CuAlO₂ have been predicted. The calculated static dielectric constant and static refractive index of 2H-CuAlO₂ is 7.1 and 2.66, respectively.

Abstract: We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, electronic structure, chemical bonding and optical properties of orthorhombic Li₂BeSiO₄. The calculated lattice parameters are in agreement with experimental data. The band structure shows a direct band gap. From the DOS analysis, charge densities and population analysis, electronic and chemical bonding properties have been studied. Furthermore, in order to understand the mechanism of optical transitions of orthorhombic Li₂BeSiO₄, the complex dielectric functions are calculated and analysed.

Abstract: The convex surface of the infrared dome is exposed to the harsh environment of the outside world, and therefore requires a coating which not only increases transmission but is able to withstand rain erosion so as to enhance system performance. This paper deals with the techniques that were developed to deposit a uniform thick SiO2 coating for sapphire dome by radio frequency magnetron sputtering. Results show that average transmission increment in wavelength range from 3 to 5um for the sapphire dome coated on convex surface was more than 4.0%. The transmission non-uniformity over the convex surface of the coated sapphire dome was less than 1.7%.

Abstract: SiO2 coatings and double layer films of SiO2/Si3N4 have been designed and prepared on sapphire (α-Al2O3) by radio frequency magnetron reactive sputtering in order to improve the optical and mechanical properties of infrared windows of sapphire. The transmission of the coated and uncoated sapphire in the wavelength range from 2.5 to 6.7um was determined. Surface morphology and roughness of coated and uncoated sapphire have been measured using a talysurf. The flexure strength of coated and uncoated sapphire samples has been studied by 3-point bending tests at room temperature and high temperatures. The results show that the coatings can improve the surface morphology and reduce the surface roughness of sapphire substrate. What’s more, the designed single layer of SiO2 film and two-layer of SiO2/Si3N4 films can both increase the transmission of sapphire in mid-wave IR and strengthen sapphire at high temperatures. Coated sapphire transmits over 95% at wavelength from 3 to 5um for the two designs. Flexure tests reveal that SiO2 coatings and SiO2/Si3N4 films increase the strength of c-axis sapphire by a factor of about 1.5 and 1.4, respectively, at 800°C.

Abstract: As a coating material with excellent optical and mechanical properties, silica films can be used as anti-reflective and protective layers on the windows and domes of sapphire. In this paper, the designed films of SiO2 have been prepared on sapphire wafers and hemisphere dome of sapphire by radio frequency magnetron reactive sputtering. Compositions and structure of SiO2 films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The refractive index of deposited films was measured and effects of the coatings on optical properties of sapphire have been studied. The results express that the refractive index of the films can be varied between 3.4 and 1.4 by changing the gas flow ratio. The deposited films can increase the transmission of sapphire in mid-wave IR greatly. The average transmittance of sapphire wafers coated with SiO2 films on both sides can be increased to 96.43 % in 3～5 µm.