This paper reports on the temperature dependent threshold voltage analysis of AlGaN/GaN High electron mobility transistors (HEMTs) in order to investigate the trap effects occurring in these devices. Measurements are performed in pulse configuration to emphasize the gate-lag and drain-lag effects involving current collapses. A quantitative extraction of the interface traps density is performed through the observation of the pinch-off voltage shifts in cold bias conditions. Additionally, a thermally activated energy level of 0.25 eV is evaluated whatever the bias condition. It is also shown that the trap density increases drastically when the drain is biased, limiting the performance of AlGaN/GaN devices through drain-lag effect.

Single crystals of urea-oxalic acid (UOA) have been grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis confirmed that the grown crystals belong to monoclinic system having space group P21/C. The presence of functional groups was confirmed by using Fourier transform infrared (FTIR) spectroscopy. Optical absorption studies show very low absorption in entire visible region and the UV cut-off is found to be around 240 nm. Thermal analysis studies were carried out using TG/DTA analysis and the grown crystal is thermally stable up to 180 °C. Dielectric constant studies confirm the ferroelectric property of the materials and very low dielectric loss reveals very high purity of the crystal.

CuInS2, CuIn3S5 and CuIn5S8 films were grown by thermal evaporation using oblique angle deposition technique. During the deposition, the substrate temperature was maintained at Ts = 150 °C and the deposition angle was fixed at α = 0° and 85°. The powders and thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). From the XRD data of powders, we calculated the lattice parameters of the structure for the different compounds. XRD patterns of thin films revealed that all samples deposited at α = 0° were polycrystalline. Indeed, CuInS2 and CuIn3S5 films had a chalcopyrite structure with preferred orientation along (1 1 2) while CuIn5S8 films exhibit a spinel structure with preferred orientation along (3 1 1). However, CuIn2n+1S3n+2 with n = 0, 1 and 2 films deposited at α = 85° were amorphous in nature. The surface and cross-section of the films were observed by AFM and SEM. The oblique angle deposition films showed an inclined columnar structure, with columns tilting in the direction of the incident flux. The surface roughness of the different films deposited, respectively, at α = 0° and 85° was determined by two methods (AFM and spectrophotometric analysis). The obtained values show an increase of the surface roughness by increasing the deposition angle α.

Aluminum nitride is a ceramic compound with many technological applications in many fields, for example optics, electronics and resonators. Contaminants play a crucial role in the AlN performance. This paper focuses mainly in the effect of oxygen when AlN, with O impurities in its structure, is grown on oxidized layers. In this study, AlN thin films have been deposited at room temperature and low residual vacuum on SiO2/Si (1 0 0) substrates. AlN films were grown by DC reactive magnetron sputtering (aluminum target) and atmosphere composed by an argon/nitrogen mixture. Working pressure was 3 mTorr. Film characterization was performed by AES, XRD, SEM, EDS, FTIR, HRTEM, SAED and band-bending method. Our results show that oxidized interlayer imposes compressive stresses to AlN layer, developing a polycrystalline deposition. Indeed, when film thickness is over 900 nm, influence of oxidized interlayer diminishes and crystallographic orientation changes to the (0 0 0 2) one, i.e., columnar structure, and stress relief is induced (there is a transition from compressive to tensile stress). Also, we propose a growth scenario to explain this behaviour.

CdSe/ZnS quantum dots and gold nanoparticles have been grown in-situ onto the surface of carbon nanotubes. The nanohybrids were then, dielectrophoretically aligned between gold microelectrodes and the electrical response was investigated. The conductance of nanotube-quantum dot hybrid was found to be sensitive to incident white light. The electrical resistance of the carbon nanotube-quantum dot nanohybrid decreased from 1.9 × 104 Ω (in the dark) to 0.91 × 104 Ω after the impact of white light. The electrical resistance of the carbon nanotube-gold nanoparticle nanohybrid was calculated to be 1.86 × 103 Ω, which is much smaller than that of carboxylated carbon nanotubes (4.03 × 105 Ω). Such a modulation in electrical properties may enhance the use of carbon nanotubes in future nanoscale devices.

In this paper, experimental results on the influence of the substrates of different refractive index on the optical properties of two-dimensional silver nanoparticle array are presented. It is shown that plasmon mode that arises from cooperative interactions between closely spaced nanoparticles exhibit different dependences on the incident angle of light. Those dependencies can be qualitatively explained by the concept of mirror images induced in a substrate. Semiconductor (ITO) substrate possesses higher refractive index which even more affects the optical response of silver nanoparticle array.

Improvements in technologies and the growing security needs in airport terminals lead to the development of non destructive testing devices using terahertz waves. Indeed, these waves have the advantage of being, on one hand, relatively penetrating. They also have the asset of not being ionizing. It is thus potentially an interesting contribution in the non destructive testing field. With the help of the VISIOM Company, the possibilities of this new industrial analysis method in assisting the restoration of works of art were then approached. The results obtained within this framework are presented here and compared with those obtained by infrared thermography. The results obtained show first that the THZ method, like the stimulated infrared thermography allows the detection of delamination located in murals paintings or in marquetries. They show then that the THZ method seems to allow detecting defects located relatively deeply (10 mm) and defects potentially concealed by other defects. It is an advantage compared to the stimulated infra-red thermography which does not make it possible to obtain these results. Furthermore, they show that the method does not seem sensitive to the various pigments constituting the pictorial layer, to the presence of a layer of “Japan paper” and to the presence of a layer of whitewash. It is not the case of the stimulated infrared thermography. It is another advantage of the THZ method. Finally, they show that the THZ method is limited in the detection of low-size defects. It is a disadvantage compared to the stimulated infrared thermography.

The development of CCS (carbon capture and storage) currently faces numerous problems and particularly the precipitation of salts induced by the drying of the porous medium during injection of carbon dioxide in deep saline aquifers. This precipitation has several consequences, and particularly the creation of a crystallization pressure which can have an important mechanical impact on the host rock. Literature on crystallization pressure is one century rich of experimental and theoretical works. However, applications have been performed in the field of civil engineering and building science only, and, despite they are of paramount importance in the context of CCS, studies about this phenomenon in deep reservoir conditions are currently lacking. In this paper, we retrieve the classic crystallization pressure equation within the framework of geochemistry and present its explicit form of dependence with temperature, pressure, and composition. Evaluation of the crystallization pressure has then been proceeded considering the injection conditions and a sketch of in-pore crystallization process. The evolution of the local stress transmitted to a crystallized pore wall is found to be strongly related to the petrophysical properties of the medium and to the injection temperature of the carbon dioxide under the assumption of constant salt concentration during the precipitation process. Values differ strongly with the considered mineral, depending particularly on the solubility, and can reach in some conditions 165 MPa, making crystallization pressure a major factor in the mechanical behavior of the aquifer.

In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded. The perfectly matched layer (PML) is widely used to simulate the truncation of the computational domain. However, its performance depends critically on an absorption function. This function is generally tuned by using case-dependent optimization procedures. In this paper, we will present some efficient functions that overcome any tuning. They will be compared using a realistic scattering benchmark solved with the Discontinuous Galerkin method.

The present paper addresses the computation of force fields inside permanent magnets that are used in many magnetic systems. The aim is to stress that magnetic behavior is not sufficient when the B-H constitutive law depends on the mechanical deformation. A full knowledge of B and H may not be enough to unambiguously compute forces. Using two expressions of magnetic energy, both admissible and giving the same B-H relationship, an application of the virtual power principle leads to two distinct force distributions. To prove this, thorough computations are performed: depending on the chosen expression huge differences on deformations are obtained.

Mixing and chaotic advection are studied in a liquid electrolyte set in motion by an electrical current passing through the fluid which is perpendicular to a magnetic field (Laplace force). Since the characteristic length in this system is very small, the inertia terms are negligible and the fluid motion is governed by the Stokes equations. Chaotic advection can occur in this flow if the potential between two electrodes is modulated time-periodically. Two tools have been implemented to characterize mixing in this flow. Poincare sections are plotted in order to distinguish between regular and chaotic regions and the advection of a blob of dye injected into the liquid is calculated and successfully compared to experiments. This very small device is shown to be an effective fluid mixer.

The aim of this work is to model the interaction of L-band electromagnetic waves with coastal breaking sea waves. The breaking sea waves’ profiles are generated using the desingularized technique and the electromagnetic waves scattering is computed using the high-order method of moments (HO-MoM) combined with non uniform rational basis spline (NURBS) geometry. Our study mainly focuses upon the electromagnetic waves behavior in the crest and the cavity of breaking sea waves.

The present work concerns the study of pulsed laser systems containing a fiber amplifier for boosting optical output power. In this paper, this fiber amplification device is included into a MOPFA laser, a master oscillator coupled with fiber amplifier, usually a cladding-pumped high-power amplifier often based on an ytterbium-doped fiber. An experimental study has established that the observed nonlinear effects (such as Kerr effect, four waves mixing, Raman effect) could behave very differently depending on the characteristics of the optical source emitted by the master laser. However, it has not yet been possible to determine from the experimental data if the statistics of the photons is alone responsible for the various nonlinear scenarios observed. Therefore, we have developed a numerical simulation software for solving the generalized nonlinear Schrödinger equation with a stochastic source term in order to validate the hypothesis that the coherence properties of the master laser are mainly liable for the behavior of the observed nonlinear effects.

In particle accelerators, the bending magnets have to be wound with flared ends. This particular shape induces an inhomogeneity in the magnetic field in the ends, which degrades the particle beam stability. This paper proposes a 3D modeling for conductors with rectangular cross-sections. The coil is first divided into blocks (parallelepipeds and arcs). Then the magnetic field is evaluated in every point of space by means of analytical formulas which allow an accurate computation. This method is also faster than numerical integrations of Biot and Savart law. Some optimization examples are finally presented and show that it is possible to minimize, with a few degrees of freedom only, the first field harmonics, integrated along the beam tube.

This article presents a time domain discontinuous Galerkin method applied for solving the con-servative form of Maxwells’ equations and computing the radiated fields in electromagnetic compatibility problems. The results obtained in homogeneous media for the transverse magnetic waves are validated in two cases. We compare our solution to an analytical solution of Maxwells’ equations based on characteristic method. Our results on shielding effectiveness of a conducting wall are same as those obtained from analytical expression in frequency domain. The propagation in heterogeneous medium is explored. The shielding effectiveness of a composite wall partially filled by circular conductives inclusions is computed. The proposed results are in conformity with the classical predictive homogenization rules.

Accurate monitoring of energy consumption is key for electrical energy management in industry This implies the use of low-cost and easy-to-install measuring chains that can be placed directly around three-phase cables without interrupting power delivery. This paper describes an innovative current measurement method using a magnetic sensor array dispatched around three-conductor cables. Analytical solution is given for the measurement problem and results from simulations.

In this paper an approach for the modeling of the eddy current testing of a conductive part with flat printed coils is proposed. The overlapping finite element method is implemented for this purpose. It is shown that this approach allows simplifying the modeling of eddy current testing configurations that use this kind of coil.

Semi-analytical models developed at Cea List for the simulation of Eddy current non-destructive testing are currently based on the volume integral equation formalism. This method is very effective for canonical geometries such as planes or cylinders since the analytical expressions of Green’s dyads are known. This approach requires three steps: the computation of the quasi-static fields induced by the probe in the workpiece without flaw, the determination of the interaction between the primary field and the defect and finally, the calculation of the response of the eddy current sensor, resulting from this interaction. In order to generalize this approach to more complex configurations, in this paper, we focus on the first step: the computation of quasi-static fields induced by an eddy current probe in a conductor with a rough surface. The semi-analytical model we generalize here is based on Maxwell’s equations, written in a non-orthogonal coordinate system resulting in the writing of the boundary conditions at the interface by using a simple analytical expression. Starting from the second-order vector-potential formalism dedicated to non-orthogonal curvilinear coordinate systems, two scalar potentials are expressed as a modal expansion, satisfying the outgoing wave condition. Finally, the coefficients of the modal expansion are determined by applying boundary conditions at the complex interface. First numerical results, obtained considering a specific configuration, are compared to other Finite Element data.

This paper proposes a criterion for locating obstacles by time reversal (TR) of electromagnetic (EM) waves based on the analysis of the density of EM energy map in time domain. Contrarily to a monochromatic study of the TR, the wide-band approach requires to determine the instant of the wave focus. This enables us to locate the focal spots that are indicative of the positions. The criterion proposed is compared to the inverse of the minimum entropy criterion as used in the literature [X. Xu, E.L. Miller, C.M. Rappaport, IEEE Trans. Geosci. Remote Sens. 41, 1804 (2003)]. An application for the localization of 3D metal targets is proposed using finite integration technique (FIT) as computational tool at the modeling stage. An experimental validation is presented for canonical three-dimensional configurations with two kinds of metal objects.