We report a study of the gate-induced spin precession in an In0.53Ga0.47As two dimensional electron gas, using a Monte-Carlo transport model. The precession vector originates from the spin-orbit coupling existing at a III-V hetero-interface, usually denoted as Rashba interaction. Contrary to the case of a one dimensional electron gas, the precession vector is randomized by the scattering events, which leads to a non negligible loss of spin coherence for an initially spin-polarized electron population moving along a conduction channel. However, we show that by operating at the liquid nitrogen temperature, or by reducing the channel width to a value close to 0.1 µm, the gate-controlled spin-polarization remains high enough to enable the investigation of the physics of spin-related phenomena in a ferromagnet/semiconductor structure.

Temperature dependence of the dielectric constant ϵ and theelectrical resistivity ρ of Rb2ZnCl4 (RZC) along the threecrystallographic axes were measured between 260 and 360 K. The electrical measurementsclearly reveal the paraelectric incommensurate phase around 303 K. Peaks in thedielectric constants ϵa and ϵb were observed at this transitiontemperature. The results of the electrical resistivity were analyzed and the activationenergies of conduction at different temperature regions were evaluated. The dependenceof the absorption coefficient α on the photon energy and on temperature near thefundamental absorption edge was measured. Exponential dependence of that coefficientaccording to the Urbach's rule was observed and the Urbach parameters were determinedand their temperature dependence was investigated. The temperature gradient of the bandgap $(\partial E_{g}/\partial T)$ reveals an anomaly at the incommensurate paraelectricphase. The indirect band gap was shifted towards the longer wavelength (red shift)with increasing temperature. This behaviour could be interpreted in terms of electronlattice interaction and crystal field splitting.

A quantitative high resolution transmission electron microscopy (HRTEM) study of amorphous materials has been undertaken in the study-case of amorphous germanium. The analysis consists in a modeling of amorphous germanium, suitable to run multislice calculations, and to simulate HRTEM images, the computed diffractograms of which are numerically compared to experimental ones obtained from a through-focus series taken on a dedicated high resolution microscope equipped with a field-emission gun. The final aim of this work is to quantify the structural information that can be retrieved from HRTEM images of amorphous materials. As a preliminary step, the coefficient of spherical aberration (Cs ) of the microscope, as well as the amount of defocus (δf) of each micrograph have to be known. The aim of the first part of this paper is to determine, as precisely as possible, these parameters. A new method is proposed, as an alternative to usual methods based on least-squares fittings of the zeros of the experimental diffractograms: the theoretical diffractograms are computed, and numerically compared, through the minimization of a profile agreement factor depending upon the Cs and δf values, and the thickness of the amorphous film, to the experimental ones. The critical steps of this approach are the modeling of the scattering of the amorphous material, and, more drastically, the estimation of the experimental thickness, which influences significantly the values of Cs and δfs.

The dependence of the current gain with the size of the emitter-base junction of double mesa Self Passivated Heterojunction Bipolar Transistors (SP-HBT) has been investigated, the extrinsic base layer being passivated with a n-type GaInP layer. The current gain is widely improved, due to a 18-fold reduction of the surface recombination in the extrinsic base region with respect to unpassivated HBT. The surface recombination current ideality factor has been found to be 1.13.

Le principal objectif de cet article est de présenter le fonctionnement destubes à gaz pulsé (TGP) par une analogie électrique [1] où la tension et lecourant représentent les paramètres hydrodynamiques pression P et débit massique m du système. Toute impédance peut être traitée comme un assemblage d'élémentsélectriques : résistance, capacitance ou inductance. À la source chaude du TGP,différents déphaseurs sont modélisés de la même manière et ainsi peuvent êtrecomparés, comme l'orifice pulse tube refrigerator (OPTR) ou tube pulsé à simpleorifice, le double inlet pulse tube refrigerator (DIPTR), le modified pulse tube refrigerator (MPTR) dont le déphaseur est un piston à la source chaude, le hybridpulse tube refrigerator (HPTR) à ouverture séquentielles d'orifices, l'inertancein OPTR (IOPTR). En combinant cette analogie électrique avec l'étude thermique ilest possible de prédire un bilan d'énergie à la source froide : puissance extraite,pertes du régénérateur, pertes du tube et influence des volumes morts. Différentessolutions peuvent être apportées au traitement de cette modélisation. Si les paramètres ne sont pas sinusoïdaux, le système peut être traité à un ordre supérieur à1. Cette modélisation a été utilisée pour la conception du tube à gaz pulsé miniaturequi travaille à des fréquences élevées 20-50 Hz et à des pressions supérieures à 20MPa, construit en collaboration avec la société “Air Liquide”. Le compresseur(rotatif ou linéaire) de demi volume balayé ≈ 1 cm3 est du type utilisésur les “Stirling”, il délivre une onde de pression quasi sinusoïdale. Sous 3 MPa depression moyenne et une fréquence de 27,5 Hz, la température limite en mode doubleinlet est de 49 K avec une puissance disponible de 1 W à 84 K.

Stray inductance in power electronics capacitors is due to themagnetic field created by the currents in winding and connections. Wereview different connection schemes that could be used in metallizedcapacitors. For each of these connections, the stray inductance expressiondepends of winding geometries. The proposed method to minimize thisinductance can be divided in two parts. The first part consists in optimizing the winding geometry for a particular connection. The second isthe choice of a low-inductance connection for the previously determinedwinding. The best results are obtained with large inner and outer radii andthrough the use of inner annular conductors.

We present optoelectronic characteristics of organic light-emitting devicesrealized by Ion Beam Assisted Deposition (IBAD) of Alq3 (8-hydroxyquinoline aluminum)layer between an ITO anode and a Ca/Al cathode. The ion type is Iodine ion and thestudy against the ion beam energy (contained between 50 eV and 150 eV) indicates anoptimization of the optoelectronic properties (internal quantum efficiency andluminance) at 100 eV while the optimized localization of the assisted layer is thearea 25–50 nm. The characteristics log (J) =f (log [V]) indicates that theinjection process takes place by trapped-charge-limited current and an estimation ofthe trap density N t leads to N t ≈ 10 14 cm−3; the enhancedoptoelectronic properties of devices obtained by IBAD are attributed to the limitationof quenching sites in the recombination area and also to charge carrier confinement atthe interface assisted layer and virgin (non-assisted) layer.

This paper deals with the automatic design of static convertersand electrical machines. Facing the multitude of such devices(converters–machines), the choice of the appropriate converter or machineis a delicate problem. A high level of expertise is required todetermine the best structure for the considered application.This choice could be rapidly made if one had a system which incorporates a greatknowledge of converters, machines and control methods.Firstly, the authors review the realized studies, then they proposethis methodology for a concrete case in order to optimize aninverter–motor of a railway traction chain. Constraints are describedin terms of input and output performances (losses, current, ...).These data are analyzed by using design rules and methods which allow thedecrease of the manufacture cost of the inverter–motor. Rules and methods areimplemented on a workstation by means of an “expert system shell” Smeci.The article proposes several tracks which involve organization, methodology, confirmation and implementation of a tool supporting a method.This process of implementation is the most efficient to fitinto a constant process of improvement which is supported by the returnon experience and by the evolution of the state of the art.

This contribution is aimed to show the Mayn results recently obtained by our group in the framework of the COST Plasma and Ion Surface Engineering (PISE) ACTION 515. Two plasma-modification processes are briefly described, namely: the deposition of thin SiOx Cy Hz gas-barrier coatings on polyethylenetherephtalate and the modification of polyethylene aimed to the surface-immobilization of anti-thrombotic molecules. Particular attention is devoted to describe how the two processes can be controlled by means of plasma- and surface-diagnostic techniques.

An analytical model for ozone concentration calculations in an oxygen-fed wire-to-cylinder ozonizer is presented in order to improve our basic knowledge on ozone generation. This approach takes into account the physical and chemical phenomena. The Becker parameter is introduced and the ozone concentration deduced from this model is compared to the Vasil'ev relation, the macroscopic coefficients for ozone formation and destruction being expressed as functions of the kinetic coefficients. The general results (electron density, ozone concentration, macroscopic coefficients) are compared with experiments and a good agreement is observed.

The production of N and H atoms has been studied in DC and HF N2-H2 flowing discharges and post-discharges in connection with nitriding of iron substrates. Experimentally, the N andH atoms have been detected by emission spectroscopy and Laser Induced Fluorescence (LIF).A strong increase of the Mayn gas atom density (N or H) was found when a small amount of a second gas (H2 or N2) was added. This increase in N or H atom densities is interpreted by a model describing the kinetics in the reactive gas volume and on the surface of the reactor walls (pyrex tube). In particular, it is shown that the destruction probabilities of N and H atoms on the tube wall are reduced by a factor of about 2 as a few % of H2 or N2 is introduced into N2 or H2. Correlations are establishedbetween the density of N and H atoms and the thickness and quality of iron nitride layers growing on iron substrates located within a reactor and placed in the post-discharge of a N2−H2 HF flowing discharge. Under the conditions of maximum N and H atom density, thick ϵ−Fe2N1−x layers without iron oxide superficial sublayer have been found on the iron surface.

An analogy between electromagnetism and acoustics is presented in 2D. Thepropagation of sound in presence of absorbing material is modeled using an openboundary microwave package. Validation is performed through analytical and experimental results. Application to local impedance active control for free fieldsound absorption is finally described.

This paper describes an experimental set-up designed to measure the conductivity of alumino-silicates melts at different temperatures up to 1650 °C. This conductivity cell has allowed to study the conductivity versus temperature of the gehlenite (2CaOAl2O3SiO2) during the solidification and fusion processes. It might be useful to improve the knowledge in glass-forming liquids.

The time dependence of the surface potential of an insulating materialis theoretically investigated in the case of simultaneous surface and volume ohmicconduction. When the material presents a constant surface conductivity, the first partof the decrease with time of the surface potential is strongly influenced by theinitial distribution of charges and cannot be used to determine the surfaceconductivity. On the other hand, at rather long times after the surface has beencharged, the potential of the surface follows an exponential variation with time, the expression of the corresponding time constant is given in different cases. This modelis found in good agreement with experiments performed with photo-oxidized epoxy resinsplaced in a humid atmosphere.