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.

Rapidly solidified Al–12.5 Si–1 Ni ribbons were prepared by melt spinning. The Si solid solubility was extended to high values as deduced from X-ray diffraction and TEM. This high solubility of Si was found to have significant effects on the various properties of this alloy. High values of electric resistivity was observed which was about four times the fully annealed values. Furthermore rapid solidification improved the tensile strength and the toughness of this alloy as compared with its classically solidified counter part. The relaxation kinetics was followed by isothermal resistivity measurements. The relaxation follows an equation which has the Johnson-Mehl-Avrami (JMA) form. No metastable phase was observed.

On one hand, the experimental crystallographic data of Chang and Read and the theoretical ones of Lieberman et al. permit a physical approach of the martensitic transformation of Au–47.5% at. Cd. On the other hand, an extension to the AuCd crystallographic system of the simple micromechanical model, developed by Lexcellent et al. for CuZnAl single crystals, allows an efficient modelling of the tension-compression and pure tension tests, performed on single crystals by Nakanishi et al. in the pseudoelastic range.

The study of thermoconvective problems in a laminar external boundary layer flow is theoretically presented for both partial heating and cooling situations after that the fluid/wall system has already reached a first steady heating state. The 4th order Karman-Pohlhausen integral approach is used under the hypothesis that the thermal boundary layer thickness is assumed to be steady during the transient phase. The final mathematical equation for both cooling and heating problems is proposed and exemples of space and time corresponding thermograms are given.

Temperature dependence of the dielectric constant ϵ and the electrical resistivity ρ of Rb2ZnCl4 (RZC) along the three crystallographic axes were measured between 260 and 360 K. The electrical measurements clearly reveal the paraelectric incommensurate phase around 303 K. Peaks in the dielectric constants ϵa and ϵb were observed at this transition temperature. The results of the electrical resistivity were analyzed and the activation energies of conduction at different temperature regions were evaluated. The dependence of the absorption coefficient α on the photon energy and on temperature near the fundamental absorption edge was measured. Exponential dependence of that coefficient according to the Urbach's rule was observed and the Urbach parameters were determined and their temperature dependence was investigated. The temperature gradient of the band gap $(\partial E_{g}/\partial T)$ reveals an anomaly at the incommensurate paraelectric phase. The indirect band gap was shifted towards the longer wavelength (red shift) with increasing temperature. This behaviour could be interpreted in terms of electron lattice 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 quenching rate constants of argon atoms in the 4p′[1/2]0−(2p1), 4p[1/2]0−(2p5), 4p[3/2]2−(2p6) and 4p[5/2]2 − (2p8) states, the upper levels of the 750.4, 751.5, 763.5 and 801.5 nm lines respectively, by H2, CH4, C2H2, C2H4, C2H6, CF4, CHF3 and SF6 have been determined. Argon atoms at room temperature are two-photon excited in the 184–190 nm range, and the decay time of the fluorescence emission is measured in the presence of various reagents. With H2, the collisional quenching rate coefficients of Ar(2p1), Ar(2p5), Ar(2p6) and Ar(2p8) are 0.27, 4.1, 6.8 and 5.4 × 10−10 cm3s−1, respectively. Therefore, in hydrogen rich plasmas, the 750.4 nm line of argon is the best suited for actinometry measurements. For the other studied molecules, the quenching rates range between 1.6 and 11 × 10−10 cm3s−1. For a correct estimation of the relative density of transient species in plasma by the actinometry technique, it is recommended to consider the collisional quenching of the upper states of the optical emission lines used.

A new experimental method aiming to the characterization of self-affine rough surfaces is presented. Based on a three dimensional reconstruction of the relief from stereo pairs obtained with a scanning electron microscope, it allows a non-destructive quantitative analysis of fracture surfaces, with a xy and z resolution only slightly lower than the original images. The roughness index of the fracture surface of an aluminum alloy is recovered, as well as the Hurst exponents of reconstructed computer-generated fractional Brownian reliefs.

The electronic and magnetic structures of the perovskite CaMnO3 are self-consistently calculated assuming two crystal structures at the same formula unit volume within the local spin density functional theory and the augmented spherical wave (ASW) method. From the comparisons of energy differences between the different magnetic states the ground state configuration is an insulator with G-type ordering. This result together with the magnitudes of the magnetic moments are in agreement with experiment. The influence of mixing between Mn and O is found spin dependent from the analysis of the crystal orbital overlap population (COOP) which enable to describe the chemical bond. The calculations underline a feature of a half metallic ferromagnet which could be connected with the colossal magnetoresistance (CMR) property of related compounds.

The oxidation at low temperature of fine-grained ferrites containing oxidizable cations such as Cu+, Fe2+, Mn2+, Mo3+, V3+, has led to new mixed-valent cation deficient ferrites with a large number of vacancies. It has been demonstrated by DTG analysis that each cation oxidizes at a specific temperature in close relation with the cation-oxygen distance. The kinetics oxidation of each oxidizable cation has been explained on the basis of a diffusion-induced stress effect when these stresses are generated by the chemical gradient induced during the oxidation process. When fine-grained ferrites contain some Co-cations, it has been revealed that the stresses have a significant influence on the enhancement of the coercivity.

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.

Higher specifications and more narrow tolerances for electrical motor appliances give sense to a renewed interest in the temperature dependence of the demagnetization curve of anisotropic ferrite magnets. Based on physical backgrounds, a first approximation modelling is given for the temperature dependence of a working point, using the room temperature curve and some material and system characteristics. A procedure is derived to give the induced shift of the whole curve at any temperature (−100 to 300 °C). An important characteristic for the application is the field Hki, where irreversible flux losses start. Hence, the critical temperature decrease, at which Hki is reached in the system, is derived.

From observations of extended dislocation nodes in β silicon nitride, possible stacking fault structures in the basal plane of this compound have been investigated. It has been found that stacking fault structure is locally analogous to α silicon nitride. A phase transformation α to β or β to α can also be achieved by cooperative shear of partial dislocations with $1/3\langle1\bar{1}00\rangle$ Burgers vectors.

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

A numerical integration scheme is presented for integration of the pressure-sensitive yield criterion due to Gurson, suitable for explicit dynamic finite element calculations. This scheme utilizes a sub-increment approach to Mayntain stability for the large strain increments and intense triaxiality that can occur under high strain rate loading. A number of validation problems are presented after which two laboratory-scale high strain experiments are simulated. The integration scheme is shown to be stable and to capture the onset of tensile fracture under high strain rate loading conditions.

Stray inductance in power electronics capacitors is due to the magnetic field created by the currents in winding and connections. We review different connection schemes that could be used in metallized capacitors. For each of these connections, the stray inductance expression depends of winding geometries. The proposed method to minimize this inductance can be divided in two parts. The first part consists in optimizing the winding geometry for a particular connection. The second is the choice of a low-inductance connection for the previously determined winding. The best results are obtained with large inner and outer radii and through the use of inner annular conductors.

The cationic composition of a titanium ferrite (Fe2.5Ti0.5O4) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally, at 450 °C, on the surface of the spinel, the α–Fe2O3 phase begins to appear and hides the ferrite.

The incorporation of silicon from SiH4 in GaAs has been studied on a wide range of growth conditions by atmospheric pressure metalorganic vapor phase epitaxy (AP-MOVPE). The highest free carrier concentration exceeds 1 × 1019 cm−3. Compensation ratios appear to be strongly dependent on the SiH4 partial pressure. The relatively high compensation ratios essentially originate from the amphoteric behaviour of silicon. The temperature dependence of silicon doping has been investigated in the range 650 °C to 765 °C with various silane partial pressures. The activation energy of Si incorporation varies from 0 to 2.2 eV. The dependence of the free electron concentration on the arsine partial pressure (PAsH3) leads to the empirical relationship: n = aPAsH3 + $bP_{AsH_3}^{-\frac{4}{3}$, which describes the relationship between silicon doping concentration and arsine partial pressure.

Preliminary results are presented from the study of grain boundary structure in bulk nanocrystalline copper using high-resolution electron microscopy. A recently developed method of image analysis is applied to an experimental image of a grain boundary between two copper grains. Maps are produced of the fringe spacing and the local rotation of the lattice as a function of position in the image. The analysis of the fringe spacing shows that no oxide layer exists between the copper grains. This confirms that the surface oxide layer coating the copper particles can be eliminated during the formation of the bulk material. By studying the way the rotation of the lattice takes place across the grain boundary, an upper limit for the interface width is obtained. The reliability and accuracy of the results are discussed.