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Physique

Nombre total de résultats : 189
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Simulation des propriétés électriques d'une cellule solaire hétérojonction à base de InGaP/GaAs

Communication

Dans ce travail, en se basant sur le model idéal pour décrire la caractéristique courant-tension et en utilisant des paramètres matériels réalistes, nous avons optimisé la performance d'une cellule solaire hétérojonction à base de composés semi-conducteur (InGaP/GaAs), en optimisant simultanément plusieurs paramètres de la couche InGaP. Notre calcul indique que le rendement énergétique maximal de la cellule étudiée peut atteindre 33.73% sous illumination 1-Soleil AM1.5 et une température ambiante. Ce dernier montre le potentiel d’une telle structure qui pourrait être une alternative aux structure traditionnelles.Voir les détails

Mots clés : simulation, Cellule solaire, couche mince, Hétérojonction, Rendement.

Structural, mechanical and optical properties of the complex K2PtCl6-structure hydrides Ba2OsH6: ab initio study

Communication

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 report a systematic investigations of the structural and optical properties of the ternary ruthenium-based hydrides Ba2OsH6 within two complementary first-principles approaches. We describe the properties of the Ba2RuH6 systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the later are available. In particular, our theoretical lattice parameters obtained using the GGA-PBE to include the exchange-correlation functional are in excellent agreement with experiment. The mechanical stability of the considered materials has been examined on the light of the pressure dependence of the elastic constants. Optical spectra in a wide energy range from 0 to 40 eV have been provided. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings.Voir les détails

Mots clés : structural, Ab initio calculations, Ternary Hydrides, mechanical properties, optical properties

Propagation characteristics of chirped Vector Solitons in birefringent optical fibers with variable coefficients in the presence of power law nonlinearity

Communication

We study in this work, the propagation characteristics of chirped vector solitons in optical fiber systems using the compact split step Padé scheme (CSSPS). This study is done in the case of variable coefficients and in the presence of power law nonlinearity. A negative chirp makes the soliton broadening, while; a positive chirp leads to a soliton compression. The effect of chirp on the soliton temporal width of an amplification system (σ>0) is greater than that in a loss system (σ<0). In the presence of power law nonlinearity, it is clearly noted that, the quintic nonlinearity has a marginal role on the propagation characteristics of the two components of managed chirped vector soliton.Voir les détails

Mots clés : vector solitons, chirped solitons, birefringent optical fibers, compact split step Padé scheme, and coupled higher-order nonlinear Schrodinger equations with variable coefficients.

Contribution à l’étude des composés FeSe2

Amar KASAA  (2009)
Mémoire de magister

Iron diselenide (FeSe2) is an interesting p-type semiconductor with a band gap of 1 eV suitable for solar cell applications. Iron diselenide (FeSe2) composite thin films have been deposited at vaccum on glass substrates by thermal evaporation technique from powder. This later was prepared by mechanical alloying of iron (Fe: 99.98 % purity) and selenium ( Se : 99.99 purity) as a function of time milling. The depositon of FeSe2 thin films on glass substrat with dimension 20 mm x10 mm. The structural evolution of a binary alloy with nominal composition FeSe2 prepared by ball milling was investigated as a function of milling time. The structural properties of the powders and the films were ascertained by x-ray diffraction method. The XRD patterns showed that for milling times up to 3 h, the FeSe2 phase is formed and appearance of Fe and FeSe. On the other hand the analysis of the films shown clearly the existance of FeSe2 with a preferential orientation according to the plan (110). The band gap Eg, estimated from optical absorption data, was between (0.8 – 1.01) eV, depending on preparation conditions such as substrate temperature. High optical absorption coefficients (> 104 cm− 1in the visible) were found. Electrical resistivity measurements show that conductivity could be analyzed in term of thermoionic emission (Seto’s model) at high temperature.Voir les détails

Mots clés : FeSe2, Cellules solaires, Evaporation thèrmique, Mécanosynthèse, couche mince

Trace and essential elements determination in baby formulas milkby INAA and k0-INAA techniques

Publication

As a part of the food analysis program executedat Es-Salam research reactor by neutron activation analysislaboratory, the concentration of As, Ba, Br, Ca, Fe, K, La,Rb and Zn in baby formulas milk have been determined byusing INAA and k0-NAA techniques. It was found that theconcentration of all elements obtained by both techniqueswas relatively identical for the three brands of the 0–6 and6–12 months of analyzed samples. In addition, the analyticalresults have been compared with those given byproducers.Voir les détails

Mots clés : Trace and essential elements, NAA method, Milk products, Analysis

Etude des propriétés structurales, élastiques, électroniques,et optiques des matériaux CuS et CuTe par la méthodeFP-LMTO

Alaa BOULEGANE  (2015)
Mémoire de magister

Nous avons présentés Dans ce travail, une étude théorique par modélisation des propriétés structurales, élastiques, électroniques, et optiques du composé CuS sous la structure Hexagonale et du composé CuTe sous la structure orthorhombique. Les calculs ont été effectués par la méthode (FP-LMTO) qui se base sur le formalisme de la fonctionnelle de la densité (DFT), en utilisant les approximations de la densité locale (LDA) et du gradient généralisé (GGA). Les propriétés structurales telles que les paramètres de maille (a) et les modules des compressibilités et ses dérivés (B0 et B’), sont calculés dans les phases hexagonale et orthorhombique respectivement. Les résultats trouvés sont en accord avec ceux avancés par l’expérience, ainsi que d’autres calculs théoriques .L’étude des propriétés électroniques du CuS,et CuTe nous a mené a des valeurs du gap d’énergie calculé par les deux approximations LDA et GGA, sont en accord avec ceux d’autres calculs.A fin de comprendre les propriétés optiques nous avons calculés la fonction diélectriqueVoir les détails

Mots clés : DFT, FP-LMTO, GGA, LDA, CuS, CuTe

FP-LMTO calculations of structural , elastic and electronic properties of CuS

Communication

The aim of this work is to study the structural,electronic and elastic properties of CuS. for this,we use the full-potential linear muffin-tin orbital(FP-LMTO) method in the framework of densityfunctionaltheory (DFT). The exchange andcorrelation energy is described in the generalizedgradient approximation (GGA ) using Perdew-Wang parameterization. We have investigated theeffect of composition on structural properties suchas lattice constants, bulk modulus and band gap.We report the results concerning the variation ofthegaps and crossover of the direct, indirect bandgap and bowing .Finally, a reasonable agreement isfound from the comparison of our results with othertheoretical calculations.Voir les détails

Mots clés : CuS, FP-LMTO, electronic properties, elastic proprieties

Studies of Iron Diselenide Thin Films Deposited by Thermal Evaporation.

Communication

Iron diselenide (FeSe2) composite thin films have been formed onto ultrasonically and chemical cleaned glass substrates by thermal evaporation technique from powder. This latter was prepared by mechanical alloying. The structural evolution of a binary alloy with nominal composition FeSe2 prepared by ball milling was investigated as a function of milling time. The structural properties of the powders and the films were ascertained by x-ray diffraction method. The XRD patterns showed that for milling times up to 1 h, the FeSe2 phase is formed. The band gap Eg estimated from optical absorption data was between 0.8–1.01 eV, depending on preparation conditions such as substrate temperature. High optical absorption coefficients (> 104 cm− 1) were found.Voir les détails

Mots clés : FeSe2, Solar energy materials, Mechanical Alloying, Thermal evaporation, Thin films

Contribution à l’étude des propriétés physiques des pérovskites dans différentes phases structurales.

Thèse de doctorat

Les matériaux de structure pérovskite ont été et font toujours l’objet de nombreuses études (les condensateurs diélectriques, dispositifs piézo-électriques, les cellules photovoltaïques). Les différentes études effectuées sur les matériaux de type pérovskite démontrent la richesse de cette famille. Peu de composées pérovskites présentent la structure idéale cubique, la maille est en fait plus ou moins déformée. Notre travail est motivé par le manque de travaux concernant différentes phases structurales des pérovskites (cubiques, orthorhombiques, hexagonales,…etc.) ainsi que la possibilité de transition entre eux. La recherche de la phase fondamentale et les propriétés physiques appropriées représentent en fait l’objectif global de la thèse. Pour accomplir ce travail, on va utiliser une méthode ab initio. La méthode repose sur la théorie de la fonctionnelle de la densité (DFT).Voir les détails

Mots clés : Perovskite, DFT, ab-initio, FP-LAPW.

Study and elaboration of silver nanoparticles supported on titanium oxide

Communication

In This work, we study silver nanoparticles supported on titanium oxide, prepared by impregnation with ionic exchange. In a first stage, the fixing conditions of the metal precursor on titanium oxide are optimized. In the second stage, the samples are calcined at various temperatures (T=250, 350, 500°C). Several experimental techniques are used for the characterization of the samples at the various stages of their elaboration (SEM, DRX, FTIR). A change of morphology of the oxide titanium grains was observed by Scanning Electron Microscope. The X-rays diffraction made it possible to evidence the formations of nanoparticles AgTi of near size 2.5nm in the case of Ag/TiO2 calcined at 250°C. At superior temperature, its size increases following the phenomenon of coalescence. The spectrometry FTIR allowed to observe peaks of vibration of links Ti-O, Ti-OH, and Ti-O-Ti.Voir les détails

Mots clés : Nanoparticules; Ag, TiO2, AgTi; catalysts.