Physique
Contribution à l’étude des composés FeSe2
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
Hollow circular cylinder: application to non destructive testing
Advanced research into non destructive control of industrial pipe works provides several acoustical methods for inspection of their structural integrity. The use of guided waves is one possible solution to detect and identify different flaws. In this paper, we are studying the propagation of guided waves in a tube and the correlation of these last by defects of surface. The dispersion curves of symmetrical modes (longitudinal and torsion) and asymmetrical mode (inflection) have been established. The mode chosen to generate it the second longitudinal mode, for this mode the radial element of displacement is very weak in front of the axial element in the point produced frequency thickness equal to 0.99 MHz.mm where from a weak attenuation, according to our experimental results the L (0, 2) mode is sensitive to the depth variation and the defect circumference. Voir les détails
Mots clés : guided waves, Hollow cylindre, NDT
Deconvolution of the transducer aperture effect in steel
When measuring the ultrasonic field, the signal provided by the receiving transducer isaffected by its spatial properties. Particularly, the displacement normal to its surface isspatially averaged because of the receiver finite size. In this study, we show, using anumerical simulation, the effectiveness of the spatial deconvolution of these effects for arectangular transducer. For that, three methods allowing the inversion of the aperture effectare tested 1) Wiener’s method 2) The power spectral equalization method (PSE) and 3) themaximum a-posteriori method (MAP).The obtained results show that the three methods areable to reconstruct the ultrasonic field from the spatially averaged values and that the qualityof the reconstruction depends strongly upon the SNR and the spatial frequencies bandwidth ofthe ultrasonic field investigated. Voir les détails
Mots clés : Deconvolution, Spatial filter, Wiener filter, power spectral equalization method (PSE), maximum a posteriori method (MAP).
Caractérisation Microstructurale d’un Alliage Al Mg Si extrudé
Le but de ce travail est la caractérisation microstructurale d’une pièce utilisée enconstruction automobile élaborée à partir d’un alliage base aluminium de la série 6000 et miseen forme par le procédé d’extrusion. Dans ce travail nous avons utilisé différentes méthodesexpérimentales (métallographie, DRX, DSC et mesures de micro dureté).La microstructure de l’alliage est formée de grains assez fins dont la taille varie entre3μm et 9 μm. elle renferme aussi une phase sous forme de précipités assez grossiers, répartisde façon homogène dans la matrice d’aluminium.Les résultats obtenus par DRX sont en faveur d’une structure cristalline cubique centrée avec un paramètre de maille de 12.64 °A. Ces caractéristiques cristallographiques correspondent à la phase dispersoides Al15 (Mn, Fe) 3 Si2, observée par d’autres auteurs surdes alliages similaires.La séquence de précipitation des phases métastables a été mise en évidence par analyse DSC et par des mesures de microdureté. Les résultats obtenus par les deux méthodes sont entrès bon accord. Voir les détails
Mots clés : Alliage série 6000, Durcissement, Zones GP
Elaboration et caractérisation des dépôts Aluminium sur Silicium(Al/Si(400))
Dans ce travail nous nous sommes intéressés à la croissance et la diffusion superficielle de l’Aluminium sur un substrat de Silicium (400). Ce travail comporte deux parties :Le première partie consiste à réaliser sous-vide et à température ambiante des dépôts de différentes épaisseurs d = 240, 510, 720, 870 et 1050 A°. Ces dépôts ont été analysés quantitativement par DRX. L’Aluminium semble croisse sur le silicium selon le mode de Frank-van Der Merwe.La deuxième partie de notre travail est consacrée à l’étude de l’effet de la température de recuit sur la morphologie des dépôts réalisés à température ambiante. Les températures de recuits sont : 100,150, 200, 250, 300, 350 et 400C°. d’après les résultats d’analyse par DRX des dépôts traités, les îlots (2D) d’Aluminium formés à température ambiante se transforment en augmentant la température de recuit, en îlots (3D) plus hauts et plus ramenés. Voir les détails
Mots clés : Évaporation thermique, Silicium, Aluminium, diffusion, DRX.
Semi-implicit operator splitting Padé method for vector HNLS solitons
We use in this paper the semi-implicit finite difference operator splitting Padé (OSPD) method for solving the coupled higher-order nonlinear Schrödinger equation, which describes the propagation of vector solitons in optical fibers. This method having a fourth order accuracy in space shows good stability and efficiency for the coupled HNLS equations describing vector solitons. We have tested this method for analyzing the behavior of optical pulses in birefringent fibers verifying that the third order dispersion TOD Voir les détails
Mots clés : Birefringence, vector solitons, optical fibers, Operator Splitting Padé Method, coupled higher-order nonlinear Schrodinger equation, third order dispersion.
GRAINS SIZE CHARACTERIZATION BY WAVES ULTRASONICFREQUENCY
In this paper we propose an experimental study of the steel grains size effect on the shiftfrequency of the ultrasonic waves being propagated in this material. By suitable heat treatment on samples resulting from the same bar, we have obtained identical samples butwith different mean grains sizes. We have then measured the ultrasonic shifts frequency after propagation in the material. The results obtained show a direct effect on the meangrains sizes on the ultrasonic frequency. These results, in conformity with the theory, showthe possibility of characterizing a material grains size by a nondestructive method:ultrasounds.It is known that a material characterization is possible through the measurement of someultrasonic parameters such as propagation velocities and attenuation coefficients. Wepropose a method which exploits the frequency and whose measurement is easy. Theseresults open way to a more inclusive and nondestructive characterization of materials byultrasounds. Voir les détails
Mots clés : ultrasonic frequency, propagation velocities, attenuation coefficients, nondestructive characterization
Design and Optimisation of Circular and Inductors for Silicon-based RFIC Application
In this paper, spiral inductors for RF application, which are designed on a silicon substrate by using standards 0.35 µ m CMOS technology, are described. Analyzed and designed with ASITIC (a tool from the University of Berkeley), which accurately takes into account the parasitic effects. This study shows the possibility of obtaining an optimal inductance having a high quality factor of 15. This result is carried out without resorting to the specific processes such as the digging of the substrate under the inductors or the use of a thick layer in gold. The use of circular form, with optimization of geometrical parameters like spacing between two adjacent turn, the track width and the number of turns, can ensure high quality factors. Voir les détails
Mots clés : circular inductor, high quality factors., RF application
Semi-implicit operator splitting Padé method for vector HNLS solitons
We use in this paper the semi-implicit finite difference operator splitting Padé (OSPD) method for solving the coupled higher-order nonlinear Schrödinger equation, which describes the propagation of vector solitons in optical fibers. This method having a fourth order accuracy in space shows good stability and efficiency for the coupled HNLS equations describing vector solitons. We have tested this method for analyzing the behavior of optical pulses in birefringent fibers verifying that the third order dispersion TOD has different effects on the two polarizations and the asymmetric oscillation is significant only in one polarization. Voir les détails
Mots clés : Birefringence, vector solitons, optical fibers, Operator Splitting Padé Method, coupled higher-order nonlinear Schrodinger equation, third order dispersion.
Analysis of HNLS Solitons with Quintic Nonlinearity Using Semi Implicit Operator Splitting Padé Method
In this communication, we use the semi-implicit finite difference operator splitting Padé method to solve the higher-order nonlinear Schrödinger equation with higher order linear and nonlinear effects such as the third order dispersion (TOD), Kerr dispersion, stimulated Raman scattering and the quintic nonlinearity. The role of quintic nonlinearity on the propagation characteristics of optical solitons is investigated for standard fibers. This method is readily generalized for nonlinear management fibers it’s found that the quintic nonlinearity has no significant role on the propagation of single solitons. Voir les détails
Mots clés : Optical solitons, Padé method, quintic nonlinearity. HNLS equation