This paper is devoted to the theoretical study of the influence of thetemperature and of the doping on the piezoresistance of N-type silicon. In the firststep the fractional change in the resistivity caused by stresses is calculated in theframework of a multivalley model using a kinetic transport formulation based on theBoltzmann transport equation. In the second step shifts in the minima of theconduction band and the resulting shift of the Fermi level are expressed in terms ofdeformation potentials and of stresses. General expressions for the fundamentallinear, π11 and π12, and non-linear, π111, π112,π122 and π123, piezoresistance coefficients are then derived. Plots ofthe non-linear piezoresistance coefficients against the reduced shift of the Fermilevel or against temperature allow us to characterize the influence of doping andtemperature. Finally some attempts are made to estimate the non-linearity for heavilydoped semiconductor gauges.

The problem of bidirectionality in bianisotropic media, i.e. existence of planeeigenwaves propagating forwards and backwards along a certain direction with the samepropagation factor is discussed. It is shown that bidirectionality in bianisotropicmedia exists for the following directions: (1) perpendicular to a plane of symmetry,(2) perpendicular to a proper axis, (3) along an improper axis, (4) parallel to anantiplane, (5) along an antiaxis of symmetry.

The effect of (Nd0.33Eu0.33Gd0.33)2BaCuO5 (NEG-211), and Gd2BaCuO5 (Gd-211) additions on melt-processed (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG-123) composites are investigated using a combination of transmission electron microscopy (TEM) and measurements of critical current densities, J c. TEM observations demonstrate that we could successfully embed submicron-size 211 particles within the NEG-123 matrix. EDX analysis revealed that thesesubmicron-size particles consist Maynly of Gd in the rare earth site. The presence ofsuch 211 particles leads to a dramatic increase of J c in low fields as wellas in the high field region. For NEG-123 with an addition of 40 mol% of NEG-211 acritical current density of 70 000 A/cm2 at 77 K, 2.2 T is observed for the fieldapplied parallel to the c axis.

Two different lead ion positions with tetragonal and orthorhombic localsymmetry were revealed in PbZrO3 ceramics on the base of 207Pb NMRspectra measurements at room temperature. The obtained data and theiranalysis on the base of the spectra shape calculations are in agreement witha symmetry of Pbam nonpolar group space of PbZrO3. The comparison ofobserved spectra in PbTiO3 and PbZrO3 with calculated spectra allowingfor resonance frequency chemical shift and spin-spin interaction show that the displacements of lead and oxygen ions are not random quantities inthe investigated PbZrO3 ceramic samples.

We have studied the effect of thickness on the structural, optical and electrical properties of In2O3:Sn (ITO) thin films. Two series of ITO thin films have been deposited onto glass substrates by DC sputtering at two partial pressures of oxygen (ppo): 4 × 10−4 and 4.75 × 10−4 mbar. Each series consists of samples with thickness ranging from 306 nm to 1440 nm. We observed a change of texture with thickness; the thinner films grow with a 〈111〉 preferred orientation; however as the thickness increased, the preferred orientation becomes in the 〈100〉 direction. The lattice constant and the grain size have also been obtained from the X-ray spectra. The energy gap, E g, has been obtained from the transmission curve; E g is found to decrease with increasing thickness for both series. The electrical resistivity ρ has been studied as a function of thickness, ppo and temperature (T). The temperature was varied from room temperature (RT) to 450 °C and back to RT; a hysteresis effect was observed in the ρvs.T curve. Also, a minimum in ρ was observed, in all these samples, in the temperature range 260 to 280 °C. For these temperatures, we have studied the effect of annealing time on the electrical resistivity for samples having both textures. We noted that ρ increased with annealing time and reaches a saturation value equal to the RT temperature value. Hall effect experiments were done on all these samples. The concentration n and the mobility μ H were obtained. These parameters are found to be sensitive to the thickness and the texture of these films. All these results will be correlated and discussed.

Al-C at% Mg alloys (C = 0.82, 1.84, 3.76, 5.74 and 12.18) have been selected forthis study. From the electrical resistivity measurements it is concluded that theresistivity increment of Al–Mg alloys (in a solid solution state) is proportional tothe atomic fractional constituents (Mg and Al) as $\Delta\rho_{\rmall}=64.66\ c(1-c)~\mu\Omegarm$  cm. In addition, both the temperature coefficient ofresistivity, α all and the relaxation time of the free electronsτ all in the alloys diminish with increasing the solute Mg concentration.The increase of the scattering power, η, with increasing C is interpreted to bedue to the contribution of electron-impurity scattering. The percentage increase dueto electron-impurity scattering per one atomic percent Mg has been determined as12.99%. The Debye temperature θ decreases as the Mg concentration increases.The microhardness results showed that the solid solution hardening obeys the relationΔHV s = 135.5C 0.778 MPa which is comparable to the theory of solid solution hardening for all alloys; ΔHV s ≈ C 0.5−0.67 MPa.

We report the molecular beam epitaxial growth of InGaP on GaAs (100) substrate using a valved phosphorus cracker cell at various substrate temperatures (T s from 420 °C to 540 °C). Sample characterization was carried out using Raman scattering (RS), photoluminescence (PL) and X-ray diffraction (XRD). Surface morphology characterization was performed using scanning electron microscopy (SEM). Typical InGaP layers showed a lattice mismatch of < 10−3 and PL full-width at half maximum (FWHM) of ~ 7 meV at 10 K. The Raman spectrum showed peaks at 330 cm−1, 360 cm−1 and 380 cm−1 corresponding to the transverse-optic (TO), InP-like longitudinal-optic (LO) and GaP-like LO modes, respectively. No Raman signals were detected from the sample grown at substrate temperature (T s) of 540 °C, due to poor surface morphology arising from indium desorption. A marginal increase in ordering, as evidenced from the slight decrease (~ 30 meV) in the PL peak energy was seen in samples grown at increasing substrate temperature. Furthermore, no significant variation in the FWHM of the LO modes, TO mode and intensity ratio of the TO mode to the InP-like LO mode were observed, suggesting that any ordering in the material grown using this technique is weak.

Due to the fast development of microelectronics, quite an important number of the chemical aspects of component formation has been occulted. In particular just a few studies are related to thin film formation in the scope of chemical reactions and modelisation. Thermodynamics itself has been implemented rather ponctually and in an incomplete way. One of the Mayn reasons for this is that thin films are considered as standingly non equilibrium systems and that. thermodynamics, as a macroscopic science, has Maynly been considered as inadequate. Thus, we have decided to reconsider the problem of thin films formation from a strictly chemical point of view.Using a simple system (formation of silicon nitride on monocrystalline silicon), the chemical reactions have been investigated.Classical thermodynamics, though inaccurate and approximate for such systems is necessary to develop the first steps of a thermodynamical model describing the deposit formation. Using a computer program helping a global treatment of several chemical reactions confirms the conclusions obtained by classical thermodynamics. We have discussed the insufficiency of the classical model, and shown that, with respect to what was experimentally observed, it was nevertheless globally valid, and that the nitride formation should be regarded as a superposition of classical chemical reactions that occurred in "close to the equilibrium" states and globally following the classical laws of thermodynamics. Thus, we propose a model of formation for the first mono layer of Si3N4 on monocrystalline silicon which is in total agreement to experimental observations.

The AC magneto-electric properties (including Faraday rotation, etc.)of a metal-dielectriccomposite are considered in the quasi-static regime.Resonances appear at modified values of the surface plasmon and cyclotronfrequencies, which depend on the applied magnetic field as well as on the microstructure.Whenthe microstructure is periodic and has more than one characteristic lengthscale, the electric permittivity can exhibit a strong dependence on boththe magnitude and the direction of the applied DC magnetic fieldin the vicinity of one of those resonances.The possibility of observing this effect in a suitably fabricatedcomposite film is discussed.

This study deals with the application of sliding mode control theory to induction machine fed by a PWM voltage source inverter in which the system operates in the field oriented control. Thus, after determining the decoupled model of the machine, a set of simple surfaces have been applied to a cascade structure and the associated control laws have been synthesized. Furthermore, in order to reduce chattering phenomenon, smooth control functions with appropriate threshold have been chosen. Simulation study is conducted to show the effectiveness of the proposed method and then validated by an experimental prototype.

Models are proposed for two major components of the coupling eddy currents, induced inRTD- HTSC power transmission cables by a time varying transverse magnetic field. Weconsider multi-layer, multi-tape cable designs in which the winding directionalternates with each layer. By assuming unsaturated operation in the tapes wecalculate resistive losses for a wide range of possible inter-tape contact resistances.Specific results are given for two hypothetical tape models corresponding tomulti-filamentary OPIT (Oxyde-Powder In Tube) and thin film IBAD (Ion Beam AssistedDeposition) elaboration processes. Conclusions are made on the constraints that theresults may take place on the future designs: particularly, on the decision whether ornot to insulate the winding layers.

Crystal Orientation Mapping (COM) is a new state-of-the-art technique for makingspatially specific orientation measurements based on the automatic analysis ofelectron backscatter diffraction patterns. The main aim of the work reported is todemonstrate the quantitative application of COM for characterising local orientationperturbations in the vicinity of triple junctions in an Al-3wt%Mg alloy deformed 5%in tension. First, the hardware configuration of the EBSD system is described and theoptimum microscope operating conditions for setting up a COM are determined bymeasuring the spatial resolution of EBSD patterns in pure Al and Ni specimens. Forthis particular investigation, an accelerating voltage of 20 kV was found to be optimum for mapping, resulting in spatial resolutions of 0.51 μm and 0.42 μmfor Al and Ni respectively. Secondly, to provide a visual representation of localorientation perturbations in the vicinity of a triple junction, a COM and patternquality map are presented. The “raw” orientation data extracted from the COM wasquantified using several different post-processing methods. The methodology associatedwith each is discussed and comparisons of the pattern of orientation perturbations aremade using the same “raw” data set.

The aim of this work concerns the development and the validation of a thermal steady state model applied to a permanent magnet direct current motor with commutator. The rated power of the machine is 120 W. Design has been realized thanks to the thermal modulus of the computation software with the finite element method Flux3D. It is shown in this work how it is possible to use only the heat equation to simulate the thermal behaviour of the motor. It implies calculating of new fluid conductivities (considering also all thermal modes) by comparison of calculated and experimental temperatures. To realize these 3D modelizations, it is necessary to know and to locate all the losses of the motor which are considered as thermal sources. The experimental temperatures are given by 40 chromel-alumel thermocouples of 100 μm diameter located in the rotor and the stator of the machine. Numerical computations use Dirichlet boundary layer conditions given by an IR camera.

The aim of this work consists in presenting a simple modelling (the molecular collision theory), easily usable in an industrial environment in order to predict the evolution of thermodynamical characteristics of the combustion of two-phase mixtures in a closed or a vented vessel. Basic characteristics of the modelling have been developed for ignition and combustion of propulsive powders and adapted with appropriate parameters linked to simplified kinetics. A simple representation of the combustion phenomena based on energy transfers and the action of specific molecules is presented. The model is generalized to various mixtures such as dust suspensions, liquid fuel drops and hybrid mixtures composed of dust and a gaseous supply such as methane or propane in the general case of vented explosions.The pressure venting due to the vent breaking is calculated from thermodynamical characteristics given by the model and taking into account, the mass rate of discharge of the different products deduced from the standard orifice equations.The application conditions determine the fuel ratio of the used mixtures, the nature of the chemical kinetics and the calculation of a universal set of parameters.The model allows to study the influence of the fuel concentration and the supply of gaseous additives, the influence of the vessel volume (2400ℓ ≤ V b ≤ 250 000ℓ) and the influence of the venting pressure or the vent area. The first results have been compared with various experimental works available for two phase mixtures and indicate quite correct predictions.

The PbO–Nb2O5 phase diagram has been investigated, using electron diffractionand high resolution electron microscopy (HREM), for [Pb]/[Nb] ratios between 1 and1.25. Apart from the basic pyrochlore structure, different long periodsuperstructures, forming a homologous series Pb2n+1Nb2n−1O7n−1 based onthe pyrochlore structure have been found. Members with n = 5, 7, 9, 11 have beenobserved and their structure determined based on electron diffraction and HREM. Imagesimulations allow studying the influence of cation and oxygen vacancies in the basicstructure. Ordering of oxygen vacancies could be detected while no cation vacanciesare observed. Deviations from the perfect structure and ordered stacking defects arediscussed.

Hematite particles have been synthesized by a one step thermohydrolysis of nitrate iron (III) solutions. The microwave system (RAMO system) designed by the authors is able to induce very fast heating rates within an autoclave. These operating conditions induce precipitation reactions in the entire volume of the reactor. These precipitation conditions lead to instantaneous nucleation of monodisperse particles (separation of the nucleation and growth events). These results indicate that it should be possible to produce very well-crystallized hematite particles which can be used as precursors for production of magnetite or maghemite.

In the present paper, we report a procedure to calculate tunnel currentsas a function of the applied voltage,by an optimization of the master equation, for a highly disordered tunnel junction array. We take a very large scatter of the tunnel resistances of the individual junctions.In order to reducethe number of equations, several approaches have still been consideredin the past. Here, we propose a procedure without any decoupling:we show that relevant results can be obtained inside and outsidethe Coulomb gap once the charge state range is automatically centered,already from a ±2 truncation of the equation set, for small offset chargesor low applied voltage. This last step is achieved in a straightforward way, through the calculation of the total tunneling rate leaving a given configuration.This has beenassessed there for the first time on a highly disordered array of five junctions.

For power applications, AlGaAs/GaAs heterojunction bipolar transistors (HBT's) were found to present high efficiency and linearity at high density RF power. We reportpower performances in S-band of a 6 × 60 µm2 one emitter finger HBTfabricated in our laboratory. At 1.8 GHz, when tuned for maximum efficiency, eachtransistor delivered a CW output power of 0.5 W (150 kW/cm2) and a power-addedefficiency of 62% and 80% in class AB and C operation respectively.The physical model based on technological and measured parametersincorporates temperature dependence for most of its parameters. It has been easilyused to analyse DC and RF power characteristics in class AB mode and to determineinput and output optimum matching cells. Good agreement between simulated andexperimental results support the validity of the model.

It is shown, both analytically and through one-dimensional numerical computations, that highly charged ions propagating through a plasma with thermal or faster than thermal velocities, drive significant ion-acoustic wakefields. By a mechanism similar to electron pairing in superconductors, such wakefields may contribute to the formation of transient molecular ions. Comparison is made with the results of experiments in which dense high temperature plasmas are created by laser irradiated colliding foils.

Dans une première partie nous avons développé un modèle d'analyse pluridisciplinaire qui établissait les dépendances fonctionnelles entre les variables de conception et les performances magnéto-électro-thermiques d'un moteur brushless à aimants permanents. Dans cet article nous décrivons une procédure de dimensionnement adaptée à la conception de la machine alimentée à fréquence variable sous faible tension. L'objectif est d'intégrer la dynamique du convertisseur électronique dès la phase initiale du dimensionnement, au même titre que les spécifications électromécaniques et thermiques. La procédure est gérée par une méthode d'optimisation déterministe de type Programmation Quadratique Séquentielle. Elle intègre l'influence du convertisseur au moyen de deux spécificités : la première consiste à évaluer les fonctions du problème d'optimisation sur la base du module d'analyse pluridisciplinaire ; la deuxième permet de contrôler l'évolution du dimensionnement au travers de variables d'optimisation dont la liste inclut les consignes de la commande en courant du convertisseur. Les difficultés d'optimisation liées au mode de fonctionnement discret du convertisseur sont discutées au regard du calcul de la sensibilité du couple électromagnétique envers la consigne de courant du convertisseur ; une méthode est proposée pour assurer la robustesse de la procédure en présence du convertisseur. L'application porte sur le dimensionnement d'un moteur à aimants permanents de type “brushless trapézoïdal" destiné à la traction d'un scooter électrique ; l'évolution de la structure optimale avec le degré de complexité du module d'analyse est mise en évidence.