[en] We used an ab initio full potential-linearized augmented plane wave technique within the density functional theory to study the structural and optoelectronic properties of Ag₂HgSnS₄ in a wurtzite-stannite phase. The exchange correlation effects are included through the generalized gradient approximation and modified Becke-Johnson exchange potential. Various physical quantities, such as lattice parameter, bulk modulus, band structure and density of states, are given. Also, we have presented the results of the effective mass for the electrons in the CB and the holes in the BV. We show that the modified Becke-Johnson exchange potential can predict the energy band gap in better agreement with the experiment. In addition the dielectric function and energy-loss function are presented for the energy range of 0-26 eV. The electronic and optical properties indicate that this compound can be successfully used in optoelectronic devices (paper)

[en] This work is devoted to excimer lamp efficiency optimization by using a homogenous discharge model of a dielectric barrier discharge in a Ne−Xe mixture. The model includes the plasma chemistry, electrical circuit, and Boltzmann equation. In this paper, we are particularly interested in the electrical and kinetic properties and light output generated by the DBD. Xenon is chosen for its high luminescence in the range of vacuum UV radiation around 173 nm. Our study is motivated by interest in this type of discharge in many industrial applications, including the achievement of high light output lamps. In this work, we used an applied sinusoidal voltage, frequency, gas pressure, and concentration in the ranges of 2–8 kV, 10–200 kHz, 100–800 Torr, and 10–50%, respectively. The analyzed results concern the voltage V_p across the gap, the dielectric voltage V_d, the discharge current I, and the particles densities. We also investigated the effect of the electric parameters and xenon concentration on the lamp efficiency. This investigation will allow one to find out the appropriate parameters for Ne/Xe DBD excilamps to improve their efficiency.

[en] Based on the density functional theory (DFT), we elucidate the origin of magnetization in non-magnetic cubic halide perovskite CsCdM₃ (M = Cl and Br) induced by substitution of non-magnetic 2p-impurities (B, C, and N) substitution. The calculations were done within the generalized gradient approximation (GGA) and GGA plus-modified Becke and Johnson (mBJ-GGA) as the exchange correlation. The results reveal that half-metallic ferromagnetism can be obtained for C- and N-dopings with the integer magnetic moment of 3.00 and 2.00 µ_B per cell. However, B substitution does not induce magnetism in both CsCdCl₃ and CsCdBr₃ systems. The localized magnetic moments substantially come from impurity atoms. The origin of ferromagnetism can be attributed to the p - p hybridization between 2p-impurities and its surrounding halide atoms. Our results show that doped perovskites could provide a new promising class of materials for future spintronics applications.

[en] Dielectric barrier discharges (DBDs) are a promising technology for high-intensity sources of specific ultraviolet (UV) and vacuum ultraviolet (VUV) radiation. In this work, the microdischarge dynamics in DBDs for Ne-Xe mixtures under the close conditions of excimer lamp working has been investigated. The computer model including the cathode fall, the positive column and the dielectric is composed of two coupled sub-models. The first submodel describes the electrical properties of the discharge and is based on a fluid, two-moments description of electron and ion transport coupled with Poisson's equation during the discharge pulse. The second submodel, based on three main modules: a plasma chemistry module, a circuit module and a Boltzmann equation module, with source terms deduced from the electric model, describes the time variations of charged and excited species concentrations and the UV photon emission. The use of the present description allows a good resolution near the sheath at high pressure and it predicts correctly the waveform of the discharge behaviour. The effects of operation voltage, dielectric capacitance, gas mixture composition, gas pressure, as well as the secondary electron emission by ion at the cathode on the discharge characteristics and the 173 nm photon generation have been investigated and discussed.

[en] In the present paper, we carried out a theoretical study of dielectric barrier discharge (DBD) filled with pure methane gas. The homogeneous discharge model used in this work includes a plasma chemistry unit, an electrical circuit, and the Boltzmann equation. The model was applied to the case of a sinusoidal voltage at a period frequency of 50 kHz and under a gas pressure of 600 Torr. We investigated the temporal variation of electrical and kinetic discharge parameters such as plasma and dielectric voltages, the discharge current density, electric field, deposited power density, and the species concentration. We also checked the physical model validity by comparing its results with experimental work. According to the results discussed herein, the dielectric capacitance is the parameter that has the greatest effect on the methane conversion and H₂/CH₄ ratio. This work enriches the knowledge for the improvement of DBD for CH₄ conversion and hydrogen production. (paper)

[en] We conducted a comparative study of various reconstructions for the (001) surfaces of SrTiO₃, BaTiO₃, SrZrO₃ and BaZrO₃ perovskites through calculations within the density functional theory. The atomic structure, the thermodynamic stability and the charge distribution of ideal AO or BO₂ terminations, as well as the so-called AO or BO₂ double layer reconstructions were analysed, and it was found that of all the BO₂ double layer reconstructions the most stable are the (2 x 2) and the (√2x√2) ones. This is mainly due to stress release through the formation of long B-chains. On Ti-based perovskites, these double layer reconstructions were found to be thermodynamically stable, which was not the case for Zr-based perovskites, for which AO terminations dominated most of the stability domain. We also found that the BO₂ double layer reconstructions are accompanied by a substantial charge redistribution, with an almost neutral surface plane. This charge redistribution has important consequences for the reactivity and the behaviour of the electric field close to the surface.

[en] We investigate the interface between Au catalysts and a Ge(1 1 1) substrate. This system is achieved by dewetting an Au layer above the Au–Ge eutectic temperature. We show by high resolution transmission electron microscopy that a large amount of Ge can be moved over a surface of Ge(1 1 1) by using assistance of eutectic Au–Ge droplets. This localization is achieved thanks to the ability of nano Au–Ge droplets to incorporate a large amount of Ge and to release it by cooling down the sample at room temperature. This makes the localization process irreversible with respect to annealing at a very high temperature. The extra Ge supplied by precipitation is in epitaxy with the Ge(1 1 1) substrate. This reflects in macroscopic I(V) measurements

[en] Nickel sulfide (NiS) thin films were deposited on the glass substrates by spray pyrolysis at 250 °C using an aqueous solution which contains nickel chloride hexahydrate and thiourea as precursors. X-ray diffraction analysis confirms that the hexagonal structure is being part of P6_3/mmc space group of the deposited films with (100) preferred orientation and lattice parameters a = 3.441 Å and c = 5.320 Å. The optical properties, investigated through transmittance and reflectance measurements reveal that the direct band gap energy (Eg) is around 0.55 eV. The electrical study shows a metallic behavior of the current II-VI binary compound. This behavior regarding NiS II-VI binary sulfide was confirmed by numerical studies based on the density functional theory (DFT) were adopted. The ground state quantities, such as lattice parameter, bulk modulus and its pressure derivative as well as the elastic constants were obtained. The values are consistent with the stability of hexagonal structure. The band structure and the states densities of such material were studied. The results show that there is an agreement between experimental and simulation. - Highlights: • NiS thin films are synthesized by Spray pyrolysis. • NiS is a low band gap compound. • These films have interesting electrical properties showing a metallic behavior. • Computational study confirms the electrical measurements