Physique
Mechanism for phosphorus deactivation in silicon-based Schottkydiodes submitted to MW-ECR hydrogen plasma
Current work reveals the deactivation mechanism of phosphorus in silicon-based Schottky diodes. Microwave plasma power(P) was fixed at 650 W to observe the variation in different operational parameters of diodes such as initial phosphorusconcentration, flux and hydrogenation temperature (TMWH) and process time (t). The analysis of variation in concentrationof phosphorus by hydrogenation has been carried out by capacitance–voltage (C–V) measurements to monitor the dopingactivation/deactivation. The results clearly show that the atomic species H+H is dominant in the reactors MW-ECR plasma.Therefore, the rates and depth of neutralization were obtained in the low phosphorus-doped silicon sample. The H becomesH0 and prefers an interaction with another H0 instead of gaining an electron to become a negative ion. The hydrogenationtemperature study indicates that the deactivation rate of phosphorus is achieved in a complex manner. Indeed, as the hydrogenationtemperatureincreases,deactivationof phosphorus also increasestill saturationat 250 °C.Athigher temperature,lowor evenno phosphorus–hydrogen complexexistsdue totheirthermaldissociation. The same behaviorwasconfirmedbylonghydrogenation. Voir les détails
Mots clés : MW-ECR plasma, Hydrogenation, phosphorus deactivation, C–V measurement
Synthesis and characterization of nickel nanoparticles supported on aluminum oxide
Due to their peculiar qualities, metal-based nanostructures have been extensively used in applications such as catalysis, electronics, photography, and information storage, among others. New applications for metals in areas such as photonics, sensing, imaging, and medicine are also being developed. Significantly, most of these applications require the use of metals in the form of nanostructures with specific controlled properties. The properties of nanoscale metals are determined by a set of physical parameters that include size, shape, composition, and structure. In recent years, many research fields have focused on the synthesis of nanoscale-sized metallic materials with complex shape and composition in order to optimize the optical and electrical response of devices containing metallic nanostructures. In This work, we study nickel nanoparticles supported on aluminum oxide, prepared by impregnation with ionic exchange. In a first stage, the fixing conditions of the nickel precursor on aluminum oxide are optimized. In the second stage, the samples are calcined at temperature (T= 750 °C). Several experimental techniques are used for the characterization of the samples at the various stages of their elaboration (SEM, DRX, and VSM). A change of morphology of the aluminum oxide grains was observed by Scanning Electron Microscope. The X-rays diffraction shows the formations of nanoparticles Al3Ni2 of near size 16.7 nm. The extracted magnetic measurements show the good and the easy magnetization Voir les détails
Mots clés : nanostructures, Ionic exchange, Nickel nanoparticles, calcination
Optimal Stochastic Excitation for Linear Flaw Detection in a Solid Material.
The field of ultrasonic nondestructive testing has known a great development during the recent years. In order to increase the faw detection sensitivity, many improvements have been made in the equipment and the sensors technology. In the present work, the optimal command which maximizes the flaw detection is investigated experimentally. A parametric optimization consisting of finding the optimal excitation frequency which maximizes the Euclidean distance between a reference medium and a medium with a linear faw has been obtained automatically by using the gradient descent algorithm. Moreover, the waveform excitation optimization has been considered. A set of stochastic signals have been transmitted to the medium. A closed loop optimization process based on a genetic algorithm allowed to find the optimal excitation without a priori knowledge on the shape of the signal. This optimal excitation converged to a sinusoidal pulse with the optimal frequency found by the parametric optimization. Voir les détails
Mots clés : Optimal command, nondestructive testing, Gradient descent algorithm, Genetic algorithm, Ultrasound
Élaboration par fusion haute fréquence et caractérisation des alliagesAl-Co-Ti.
L’objet de ce travail de thèse est d’étudier l’effet de l’addition du cobalt à l’aluminium pur,pour une teneur en titane constante, sur le comportement microstructural, mécanique,thermique et électrochimique. Ce système d’alliage Al-Co-Ti a été élaboré sous inductionélectromagnétique à haute fréquence et sa caractérisation présente des phases intermétalliquescomplexes telles que Al13Co4, Al9Co2 et Al5Co2. L’addition du cobalt à l’aluminium faitégalement apparaitre une structure quasi cristalline pour les alliages contenant 20%Co et25%Co. Par ailleurs, l’analyse électrochimique montre l’importance de la composition à15%Co par rapport aux autres alliages du point de vue de la tenue à la corrosion. Voir les détails
Mots clés : alliage Al-Co-Ti, élaboration, induction magnétique, microstructure, DRX, dureté, corrosion.
Characterization and valorization of steel co-products
The iron industries generate large quantities of slags and mill scale at different scales. We have focused on the physicochemical characterization of slag and battitures from the El Hadjar sideal complex. To evaluate the quality of these co-products, we first used particle size analysis by the laser method followed by density measurements. Finally a microstructural analysis by X-ray diffraction has been completed. Voir les détails
Mots clés : slag, Battitures, valorization, characterization
One-dimensional Parametric Study of Damage Detection in a Solid Material using a Nonlinear Wave Modulation Spectroscopy (NWMS) Technique.
Nonlinear Wave Modulation Spectroscopy (NWMS) is one of the most powerful techniques used to detect damage in materials. It consists in simultaneously applying two continuous waves with different frequencies, the one high, f2, and the other low, f1. When the material is damaged, the frequency spectrum exhibits harmonics and sidebands which are located at (f2 + f1) and (f2 - f1). This paper presents a parametric simulation study of the nonlinear propagation of elastic waves in solid media, which can be represented by a one dimensional mass-spring system. The system of motion equations is resolved by a fourth order Runge-Kutta iterative method. A quadratic nonlinearity can be introduced locally in the system at any spring. The objective of the paper is to highlight the ability of the nonlinear acoustic methods, especially the NWMS (Nonlinear Wave Modulation Spectroscopy), to detect damages in solid material. The study of the evolution of the sidebands amplitude, according to the low frequency of the wave (pump wave), f1, in cracked and intact material will be presented. It is shown that this amplitude reaches a maximum when the pump frequency corresponds to a resonance frequency of the system. In addition, the study shows the strong dependency of the resulting frequency spectrum of the received signal upon the nonlinearity magnitude as well as the rigidity of the simulating crack spring. Voir les détails
Mots clés : Nonlinear Modulation Spectroscopy, Damage detection, nonlinear wave propagation simulation
Complexity reduction of ultrasound sub-ultra-harmonic modeling by an input modified volterra approach
Contrast of echographic images has been highly improved by the injection of microbubbles, due to their nonlinear behavior. However, this contrast enhancement is limited by the nonlinear acoustic propagation in tissue. To overcome this drawback, sub and ultra-harmonic contrast imaging can be used, since only microbubbles can generate these components. Nonlinear modeling is a primordial step in the analysis of microbubble signals for sub and ultra-harmonic imaging. Nonlinear models like Volterra model has been applied in harmonic imaging to model harmonics optimally. However, it can model harmonics only. For sub and ultra-harmonic modeling, a multiple input single output (MISO) Volterra has been proposed. The aim of this study is to propose a simpler alternative for the modeling of sub and ultra-harmonics. We propose a modified single input single output (SMISO) Volterra model based on input demodulation. The model is tested using simulated and experimental signals. Results showed that sub and ultra-harmonics are modeled. The number of kernels is reduced to its half using SMISO model compared to MISO model. The relative mean square error between the simulated signal and the modeled signal with SMISO Volterra model is -15.8 dB and it is -60.7 dB for experimental signals. The computational time is reduced by a factor of 4 and 5 in simulated and experimental cases respectively. SMISO model can make easier the sub and ultra-harmonics modeling. Voir les détails
Mots clés : Non lineaire acoustics, contrast enhancement
ELABORATION ET CARACTERISATION DES COUCHESMINCES SUR LES ACIERS PAR LES METHODES NONDESTRUCTIVES
Le but de cette étude est l’évaluation et la caractérisation par les méthodes non destructives, les courantsde Foucault et les courants de Foucault pulsés, l’effet des traitements thermiques sur des aciersfaiblement alliés et des aciers inoxydables duplex ainsi que sur des couches minces élaborés parélectrodéposition.Des caractérisations structurales par microscope électronique à transmission (MET), des caractérisationsmécaniques (dureté, résilience,…) et électrochimiques ont été effectuées sur les aciers traités.Les couches minces protectrices contre la corrosion sont élaborées à partir d'un bain de nickel et del'alumine avec une variation de la quantité d'alumine de 5-20g / l. La morphologie de la surface et lamicrostructure des revêtements Ni-Al2O3 ont été déterminées au moyen de la microscopie électroniqueà balayage (MEB) et de la diffraction des rayons X (XRD). Les résultats obtenus de la mesure de ladureté par nano-indentation, la mesure de l'épaisseur et les essais électrochimiques ont abouti à uneaugmentation de la résistance à la corrosion lorsque la quantité d'alumine augmente. Il a été trouvé unebonne corrélation entre les résultats obtenus à partir des essais non destructifs et les méthodestraditionnelles. Voir les détails
Mots clés : corrosion, revêtement, traitement thermique, contrôle non destructif, couches minces.
SIMULATION STUDY OF SUPER-RESOLUTION IN HYDROPHONE MEASUREMENTS OF PULSED ULTRASONIC FIELDS
In order to carry out reliable measurements of pulsed ultrasonic fields, the use of a piezoelectric hydrophone as receiver is recommended. However, due the finite size of the receiver aperture the measured acoustic pressure is affected by spatial averaging on the surface active face. The aim of this work is to deconvolve the spatial effects of the receiver hydrophone in order to reconstruct the pulsed ultrasonic field with a better spatial resolution. Hereby, the linear pulsed pressure field radiated in water by wideband planar transducers of 19 mm diameter, with central frequencies fc=2.25 MHz and fc=15 MHz are considered. The receivers are PVDF membrane hydrophones of 25 µm - thickness with rectangular and circular apertures. The results of this study show the strong dependency of the reconstruction quality upon the signal-to-noise ratio (SNR). Generally, the quality of the reconstruction decreases with decreasing SNR. Good reconstruction quality has been obtained with correlation coefficient larger than 0.9936 when the “acquired” signals are not too much noisy (SNR=60dB). In this case, improvement of the spatial resolution by a factor of 5 and 9 respectively could be reached. The reconstruction quality depends also upon the hydrophone dimensions, the axial distance to the source, the central frequency and the spectral frequency bandwidth of the pressure pulse. Voir les détails
Mots clés : Super-resolution, spatial inverse filter, spatial Wiener filter, PVDF hydrophone, pulsed ultrasonic field, ultrasonic field reconstruction.
Description of the solid method of BaTiO3 ceramics elaborations
Abstract— There are two major methods of the barium titanate ceramic BaTiO3 elaboration, the solid and the liquid methods (Hydrothermal, sol-gel processing, and Coprecipitation) [1, 2, 3].In this work, we present a theoretical study to describe the solid method of BaTiO3 elaboration, it is the most method used in the industry, because it is very economical, inexpensive and easier to implement. Voir les détails
Mots clés : component formatting; style; styling; insert