Physique
FINITE ELEMENT ANALYSIS OF AlN/Si THIN FILM RESONATOR
This paper aim to study the influence of thin film thickness on the surface acoustic wave and reflectivity in AlN/Si resonator with Al electrodes, using finite element analysis. Mode shapes of the device as a function of frequency thickness were presented and results were obtained to optimize the design of SAW thin film devices that can work in high frequency. Voir les détails
Mots clés : Surface acoustic wave, thin film resonator, FEM analysis
Structural, elastic, electronic and chemical bonding properties of the semi-conductor matérials Ba2OsH6: An ab initio study
Several applications of hydrides have been found so far. During the last decade, applications such as hydrogen storage/economy [1,2], rechargeable batteries [2], etc., have been the subject of intensive research efforts. After the discovery of the switchable optical properties of yttrium and lanthanum hydride films [3], hydrides have found another application as smart windows [3–4]. For the above listed specific applications of hydrides fast kinetics of hydrogenation/dehydrogenation processes, low temperature at which the hydrogenation/dehydrogenation occurs, large hydrogen content, low total weight and powder form of hydrides are extremely important. However, hydrides with large total weight, low concentration of hydrogen atoms and high temperature for activation of hydrogenation/dehydrogenation processes have received little or no attention. Recently, this class of hydrides has been suggested as a source of important applications in semiconductor electronics, such as transparent conducting materials [5] and semiconductor p–n junctions [6]. Voir les détails
Mots clés : structural, elastic, electronic, chemical bonding ab initio calculations, Electronic band, densities of states, Charge density.
Theoretical estimation of the production of biogasfrom the landfill of Batna city and its electricalconversion by a SOFC
Amongst the interests in fuel cells is exploring the possibility of using different fuel types;one of them is biogas or Landfill gas (LFG) from landfills or from controlled digesters.Biogas; a gas produced by an anaerobic digestion of organic waste represents an environmentalproblem that could turn to a renewable energy source. The valorization ofbiogas into energy (electricity, heat, fuel) will save other sources of energy. The authors ofthe study are interested in evaluating three technologies: fuel cells, micro turbines andinternal combustion engine.In this paper, we discussed the conversion of biomass into electricity in two steps: thefirst step (biomass-to-biogas) is based on an evaluation of biogas potential generated bysolid waste of landfill the Batna city (Algeria) by the kinetic model (U.S.EPA, 1993). In thesecond step (biogas-to-electricity), the paper considers the technology of a stack of standardsolid oxide fuel cells (Ni-YSZ/YSZ/LSM) SOFC; this allowed us to determine the besttemperature, hydrogen concentration and electrolyte thickness for maximum powerdensity in the fuel cell SOFC. At a temperature T = 1273 K and thickness of electrolyte of theorder of 0.1 mm and at higher hydrogen concentration, a maximum power density ofP = 1.4 W/cm2 was obtained. Voir les détails
Mots clés : LFG, Biogas, Anaerobic digestion, Electricity, SOFC
Characterization of the deformation texture after tensile test and cold rolling of a Ti-6Al-4Vsheet alloy
The deformation texture after cold rolling and tensile test of an industrial Ti-6Al-4V sheet alloy was studied using X-ray diffraction. The alloy was subjected to a cold rolling to different thickness reductions (from 20% to 60%) and then tensile tests have been carried out along three directions relatively to the rolling direction (0°, 45° and 90°). The experimental results were compared to the existing literature and discussed in terms of active plastic deformation mechanisms. Voir les détails
Mots clés : TA6V, deformation texture, Anisotropy, Lankford
First-principles calculations of the structural, electronic and optical properties of In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS
The structural, electronic, and optical properties of the cubic In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS have been investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). The generalized gradient approximation (GGA) of Wu and Cohen was used as the exchange correlation potential to calculate the structural and electronic properties. In addition, the alternative GGA proposed by Engel and Vosko and the modified Becke–Johnson potential are utilized to calculate the electronic properties. The computed structural and electronic properties of the binary compounds are in good agreement with the available experimental and theoretical data. For the alloys, non-linear variations of composition x and y with the lattice constant, bulk modulus, direct, indirect band gap, dielectric constant and refractive index are found. All the compounds are direct band gap excluding BP and BAs. The energy band gap of In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS substrates is computed. Finally, the band gap of our materials is less than 3.1 eV. Thus the In1−xBxAsyP1−y quaternary alloys may possibly be used in visible light devices. Voir les détails
Mots clés : FP-LAPW, DFT, In1−xBxAsyP1−y quaternary alloys, Lattice matched
First-principle calculations of the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu–Cohen generalized gradient approximation (WC-GGA) and Perdew–Wang local density approximation (LDA) were used for the exchange–correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures Voir les détails
Mots clés : FP-LAPW, DFT, energy band structure, Thermal Properties, Debye model, critical temperature
Optimization of Optical Gain in Inx Ga1-xSb/GaSb unstrained quantum well structures
In this paper we study the effects of In concentration, temperature, quantum well width and carrier density on optical gain for GaSb/InxGa1-xSb/GaSb untrained quantum well structures. This system was chosen as it is useful in infrared emission, finally, we introduce the optimum structure of quantum well to obtain the maximum optical gain, at room temperature and infrared emission particularly 2.3 (μm), for the use this structure in application of spectroscopic analysis of the gases specially CH4. This structure can be used for light absorption to increase the solar cell efficiency a based on a quantum well and multi-junction. Voir les détails
Mots clés : Quantum well, In1-x Gax Sb, optical gain, laser, Detection
Effects of stabilizer ratio on photoluminescenceproperties of sol-gel ZnO nano-structured thin films
Nanostructured ZnO thin films with different molar ratios of MEA to zinc acetate (0.5, 1.0, 1.5 and 2.0) have been deposited on glass substrates by a sol–gel dip coating technique. X-ray diffraction, Scanning Electron Microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy have been employed to investigate the effect of MEA stabilizer ratio on structural, morphological, absorbance and emission properties of the ZnO thin films. Diffraction patterns have shown that all the films are polycrystalline and exhibit a wurtzite hexagonal structure. The c axis orientation has been enhanced with increasing stabilizer ratio. SEM micrographs have revealed that the morphology of the ZnO films depend on stabilizer ratio. The UV–visible absorption spectra have demonstrated that the optical absorption is affected by stabilizer ratio. The photoluminescence spectra have indicated one ultraviolet and two visible emission bands (green and red), while band intensities are found to be dependent on stabilizer ratio. ZnO thin films deposited at MEA ratio of 1.0 show the highest UV emission while the minimum UV emission intensity is observed in thin films deposited at ratio of 0.5 and the maximum green has been recorded for films deposited at MEA ratio of 2.0. Voir les détails
Mots clés : ZnO thin film, Sol–gel, Stabilizer ratio, Photoluminescence
Degradation of plastic pipe surfaces in contact with an aggressive acidic environment
olyethylene (PE) pipes transporting water are vulnerable to aggressive agents which are able to diffuse through buried plasticpipes causing oxidative degradation. The latter may occur as a result of a spontaneous chemical reaction with atmospheric oxygen or as an induced oxidizing reaction with disinfectant agents (i.e. chlorine or hypochlorous acid ions) which are commonly added to municipal water supplies for public health reasons. Basically, PE pipes surfaces undergo undesired oxidation reactionswhenever they are in contact with adverse external environments and/or when conveying fluids which tend to modify internal pipe wall structure. In this work, the effects of distilled water and diluted hydrochloric acid at different concentrations on the external and internal surfaces of a high density polyethylene (HDPE-100) pipe are studied. The measured parameters are roughness and hardness in order to appreciate surface quality variances in as-received and degraded materials. Initially the outer surface is rougher than the inner’s one but in contact with distilled water, the external surface roughness increased by 6% although the internal face of the tube revealed a small decrease (<5%). When exposed to hydrochloric acid, pipe roughness (μm) showed a substantial increase as a function of increasing medium concentration. Crystallinity (χ in %) measurements confirmed the gap between outer (51.55%) and inner (61.31%) surfaces indicating that degradation has taken place at the structural level when HDPE was in contact with such aggressive agents. On the other hand, it is revealed that after exposure to oxidizing environments, crystallinity dropped by approximately one third when compared to as-received material; therefore reducing resistance to fracture and subsequently pipe lifetime. Voir les détails
Mots clés : polyethylene pipe; environment; distilled water; diluted hydrochloric acid; degradation; surface roughness; hardness; crystallinity.
The effect of copper concentration on CdS/CZTSheterojunction properties
Cu2ZnSnS4 (CZTS) / CdS heterojunctions have been prepared by a successive deposition of CZTS and CdS thin films on glass substrates by spray pyrolysis and chemical bath deposition techniques respectively. The concentration of cupric chloride in the starting solution has been varied in order to investigate its influence on device properties. The realized CZTS/CdS heterojunctions were characterized by recording their IV characteristics at ambient and at different temperatures. The current-voltage (IV) characteristics of the different heterostructures exhibit a rectifying behavior with a good ideality factor ranged from 1.5 to 2.7. From these IV characteristics we have deduced the saturation current series resistance and barrier height of the devices. We found that these quantities vary from 0.22 to 1.68µA for the saturation current and from 300 to 2500 for the series resistance. We have deduced also that the potential barrier was found between 0.3 and 1.31eV. From these results we inferred that the realized structures are suitable for their applications as solar cells. Voir les détails
Mots clés : CZTS; heterojunction; spray pyrolysis; solar cells;IV