Physique
Contribution à l’Etude de Phénomène de Diffusion à l’Interface des Couches Minces Ni/Si(111) Formées par Evaporation par Effet Joule.
L’objet de notre étude ici, est la maîtrise de la fabrication des alliages Ni-Si par Evaporation par Effet Joule (PVD) sous forme de couches minces sur un substrat en silicium. Pour cela, en premier lieu, nous avons étudié les différents paramètres influençant la formation des couches minces métalliques déposées sur un substrat de silicium par évaporation par effet Joule. Ces paramètres sont : La pression d’évaporation (P), vitesse de pompage (Vp), courant de chauffage (I) et vitesse du dépôt (Vd). La vitesse de dépôt atteint 0,1 à partir de 155 A, considérée comme étant le début d’évaporation du métal.Dans ce travail, la réaction à l’état solide entre un film mince de nickel d'épaisseur 1250 Å déposés sous vide sur un substrat de silicium Si (111), a été étudiée au moyen de la diffraction des rayons X, la microscopie électronique à balayage et la rétro diffusion des particules alpha. Ces échantillons ont subit ensuite des traitements thermiques sous vide 200, 350, 400, 600, 750 et 800°C pendant 45 minutes. Les résultats montrent la croissance et la formation des siliciures. Nous remarquons après le recuit à 800°C, la seule Phase qui apparaît est le NiSi2, riche en Silicium : Ceci indique que le nickel et le silicium se sont totalement mélangés dans la matrice du silicium, comme il a été confirmé par l’analyse RBS. Voir les détails
Mots clés : diffusion, Nickel, couches minces, siliciures, DRX, RBS, résistivité.
Structural, elastic, electronic and chemical bonding properties of the semi-conductor materials X2OsH6 (X = Mg and Ca): An ab initio study
Several applications of hydrides have been found so far, e.g. switchable mirrors [1–2], energy storage [3,4], rechargeable batteries [4], etc. Using first-principals density functional calculations, we have studied the structural, electronic elastic and elastic properties of the complex hydrides Mg2OsH6, Ca2OsH6. The calculated structural properties; namely equilibrium lattice constants, internal free parameters, bulk modulus and its first-order pressure derivative, are in good agreement with the available results. The relative changes of the structural parameters versus hydrostatic pressure have been investigated. The elastic constants and their pressure dependence are predicted using the static finite strain technique and the polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus, Young’s modulus and Poisson’s coefficient, Lames coefficients, average sound velocity and Debye temperature are numerically estimated in the frame-work of the Voigt–Reuss–Hill approximations. The mechanical stability of the considered materials has been examined on the light of the pressure dependence of the elastic constants. The elastic anisotropy of the X2OsH6 has been studied using three different methods. The analysis of the site and momentum projected densities, charge transfer and charge densities show that bonding is of covalent-ionic nature. The band structures show that all studied materials are indirect energy band gap semiconductors. Voir les détails
Mots clés : semi-conductor, structural, elastic, electronic, chemical bonding ab initio calculations, Electronic band, densities of states, Charge density.
Structural, elastic, electronic and chemical bonding properties of hydrides X2RuH6 (X = Mg and Ca): An ab initio study
Several applications of hydrides have been found so far, e.g. switchable mirrors [1–2], energy storage [3,4], rechargeable batteries [4], etc. Using first-principals density functional calculations, we have studied the structural, electronic elastic and elastic properties of the complex hydrides Mg2RuH6, Ca2RuH6. The calculated structural properties; namely equilibrium lattice constants, internal free parameters, bulk modulus and its first-order pressure derivative, are in good agreement with the available results. The relative changes of the structural parameters versus hydrostatic pressure have been investigated. The elastic constants and their pressure dependence are predicted using the static finite strain technique and the polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus, Young’s modulus and Poisson’s coefficient, Lames coefficients, average sound velocity and Debye temperature are numerically estimated in the frame-work of the Voigt–Reuss–Hill approximations. The mechanical stability of the considered materials has been examined on the light of the pressure dependence of the elastic constants. The elastic anisotropy of the X2RuH6 has been studied using three different methods. The analysis of the site and momentum projected densities, charge transfer and charge densities show that bonding is of covalent-ionic nature. The band structures show that all studied materials are indirect energy band gap semiconductors. Voir les détails
Mots clés : structural, elastic, electronic, chemical bonding ab initio calculations, Electronic band, densities of states, Charge density.
ELABORATION AND CHARACTERIZATION OF ZnO THIN FILMS DEPOSITED BY DC SPUTTERING AT LOW PRESSURE AND LOW TEMPERATURE:APPLICATION TO PHOTOVOLTAIC AND GAS SENSOR
DC reactive sputtering was used to deposit Zinc oxide (ZnO) films onto corning glass and crystalline silicon substrates at both room temperature and 100°C with an argon/oxygen mixture at sputtering pressure varying from 10 to 70 Pa. The dependence of films properties including structure, microstructure as well as optical on deposition parameters (deposition temperature and sputtering pressure) are investigated. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmission, electrical conductivity measurements. All ZnO films exhibit an intensive (002) XRD peak, indicating that the films are highly texturized along the c-axis perpendicular to the substrate surface. It is found that the nature of the annealing atmosphere has a great influence on the ZnO film composition. Furthermore, thermal annealing at 300°C have the effects of narrowing the diffraction peak and shifting the (002) peaks to higher 2θ angles, which indicates that grain growth has occurred. The transmission measurements have shown that all films exhibit high transmittance in the 400–2500 nm range. Post-deposition annealing influences the morphological, optical and electrical properties of ZnO films. A very large increase in electrical conductivity, up to nine orders of magnitude, was observed in as-grown ZnO films upon vacuum-annealing at 300°C for one hour, reaching as high as 10 ?-1.cm-1. Voir les détails
Mots clés : reactive sputtering, transparent conducting zinc oxide, optical properties, structural characterization, electrical conductivity.
LES PROPRIETES OPTIQUES ET ELECTRIQUES DES COUCHES MINCES DE ZnO DEPOSEES PAR PULVERISATION CATHODIQUE A BASSE PRESSION.
Les propriétés des couches minces de l’oxyde de zinc (ZnO) (optiques, électriques) déposées par pulvérisation (DC) dépendent fortement des conditions de dépôt comme la composition de phase du gaz, les conditions de plasma et la température de dépôt. Des couches minces de ZnO ont été déposées par pulvérisation (DC) d'une cible métallique de Zinc en utilisant un plasma d’un mélange de gaz (argon, oxygène) avec une pressions totale ne dépasse pas 1 mbar et à une température de 100 ° C. Ces couches sont caractérisées par la transmission optique UV visible, mesures de conductivité électrique, mesures Raman. Les mesures de transmission optique des couches montrent que la transmission optique est très élevée (facteur de transmission) dans la gamme de longueurs d’ondes située entre 400nm et 2500 nm et elle variée en fonction des conditions d’élaboration comme est présenté sur la figure 2a. Les mesures électriques I-V et I-T mettent en évidence l’effet de la pression dans la chambre de dépôt sur la conductivité et l’énergie d’activation des couches élaborées. Voir les détails
Mots clés : pulvérisation réactive, oxyde de zinc, propriétés optiques, caractérisation structurale, conductivité électrique.
Precipitation kinetics and mechanical behavior in a solution treated and aged dual phase stainless steel
The precipitation kinetics and the mechanical behaviour in a solution treated and aged dual phase stainless steel (DSS) are investigated. X-Ray diffraction, transmission and scanning electron microscopy techniques are used to characterize the microstructure and to identify its constituents. The precipitation kinetics analysis shows that the ferrite to σ phase transformation follows the modified Johnson Mehl Avrami (JMA) model containing an impingement parameter c that is adjusted to 0.3. Activation energies calculation leads to conclude that interface reaction is the main mechanism that controls the σ phase formation. Detailed analysis of the extent of the different tensile deformation domains reveals the significant contribution of both σ phase particles and dislocation accumulation to the strain hardening of the material Voir les détails
Mots clés : alloys, aging, microstructure, mechanical properties
Spatial convolution of a stress field analyzed by X-ray diffraction
X-ray stress analysis suffers from homogeneity limitations of the stress field in the analyzed volume. When this homogeneity is not fulfilled, it is possible to reduce the irradiated volume down to stress homogeneity achievement. New limitation however occurs : the diffracting sites become too few for stress homogenization. We show that the diffractometry analysis corresponds to a spatially convoluted stress field. The inverse convolution problem is posed. An example of regularization method is given. Voir les détails
Mots clés : XRD stress measurement, spatial convolution, stress gradient, inverse problem
Chemical Sensor Array Modeling: Application to Resistive Based Chemo Sensors
The aim of paper is to develop analytical mathematical models that describe the thermo dynamical equilibrium of resistive chemical sensor arrays /mixture of vapors multi-system. By using the Gibbs Duhem formalism, state equations in differential form, that the variations of intensive quantities (e.g. sensors partial sensitivity) as function of the gas mixture components concentrations and sensor array parameters describe, have been developed. Moreover, the responses of the sensor arrays as function of gas mixture components concentrations were modeled. Voir les détails
Mots clés : resistive chemo-sensors, sensor array, vapors mixture, modeling, Metal Oxide Sensors (MOS), Conducting Polymer Sensors
NONDESTRUCTIVE EVALUATION OF THE CARBON CONTENT IN STEEL
The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity Voir les détails
Mots clés : carbon content, steel, ultrasonic waves.
Champ thermique sous l'effet de la réaction chimique d'une réforme de la pile à combustible à oxyde solide SOFC DIR-interne direct
Les effets directs de reformage interne dans une pile à combustible à oxyde solide (SOFC) sur les champs thermiques sont étudiés par modélisation mathématique. Cette étude présente les champs thermiques d'une pile à combustible standard (Ni-YSZ / YSZ / LSM) anode en charge. Cette étude est également faite dans le plan perpendiculaire à l'écoulement des gaz. La pile à combustible est alimenté par de l'air et de carburant, CH4, H2, CO2, CO et H2O où la naissance du phénomène de la réforme (DIR-SOFC) interne direct. Il est basé sur la réforme de réactions chimiques, de la vapeur et de réaction de reformage réaction du gaz à l'eau. Le but principal de ce travail est la visualisation des champs de température sous l'influence des réactions chimiques mondiales et la confirmation du comportement thermique de cette réaction chimique. Les champs thermiques sont obtenus par un programme informatique (Fortran). Voir les détails
Mots clés : SOFC, Direct internal reforming, Global chemical reactions, Thermal fields