Crack-free lattice-matched Al0.85In0.15N/GaN heterostructures were grown on sapphire substrates with barrier thicknesses up to 100 nm which exhibit very high polarization-induced electron sheet density ( ${>}2.5\times 10^{13}$  cm−2) located at the heterointerface. These layers have been further processed as high electron mobility transistors (HEMTs). Optical characterization of these structures was carried out by photoluminescence and microphotoluminescence ( ${\rm \mu} $ PL) for different biased voltages. The insertion of an InGaN back-barrier unambiguously reveals that spatially direct optical recombinations occur within the AlInN alloy. Since the GaN excitonic bandgap is very sensitive to local temperature changes, the ${\rm \mu} $ PL technique allows mapping very precisely the actual local temperature distribution in biased HEMT devices. For a gate length of 1.5  ${\rm \mu }$ m temperatures up to 1130 K were found at a drain-source voltage of 20 V thus indicating the presence of a hot phonon bath.

Modulation doped heterostructures GaAs/GaAs $_{1-x}$ Nx /GaAs/Al0.3Ga0.7As:δSiwith GaAs $_{1-x}$ Nx Quantum Wells (QW) with different nitrogen contents x have been grown by molecular beam epitaxy and investigated by photoluminescence (PL) spectroscopy. We have found that at low temperature the photoluminescence spectra are essentially formed by two structures observed at 1.51 eV and 1.47 eV attributed to excitonic transitions in GaAs layer, and in GaAs $_{1-x}$ Nx QW, respectively. The Band Anticrossing Model (BAC) has been adopted in order to confirm the nature of the transitions in GaAs $_{1-x}$ Nx QW's. The band structure of $\delta $ -doped GaAs/GaAs $_{1-x}$ Nx /GaAs/Al0.3Ga0.7As:δSi has been studied theoretically by using the finite differences method to self-consistently and simultaneously solve Schrödinger and Poisson equations written within the Hartree approximation. We find in this way good agreement between our measured and our calculated values for the transition energies in our GaAs $_{1-x}$ Nx  QW's.

The present work is concerned with the development of etch pits on (hk0) and (hh $\ell$ ) silicon surfaces immersed in various etchants. Final shapes of small etch pits are found to be bounded by {111} facets solely. The orientation dependence of etching shapes is explained in terms of a kinematic and tensorial model involved in the simulator TENSOSIM. An agreement between experimental and theoretical etching shapes is observed showing that the simulator can generate quite accurate 3D etching shapes for pits blocked by limiting facets. After a fair adjustment of the database the simulator derives also etching shapes close to experimental shapes of large pits.

This paper is devoted to the study and the characterization of novel magneto-optical waveguides prepared via organic-inorganic sol-gel process. Thin silica/zirconia films doped with magnetic nanoparticles were coated on glass substrate using dip-coating technique. After annealing, samples were UV-treated. Two different techniques were used to measure their properties: m-lines spectroscopy and free space ellipsometry. Results evidence low refractive index waveguides that combine a low modal birefringence (2×10−4) with a Faraday rotation around 15 °/cm (ϕ = 0.1%). The low birefringence is obtained with a soft UV treatment and a graded intrinsic anisotropy is evidenced for films thicker than 5 μm. Therefore, we prove that the organic-inorganic sol-gel approach is very promising to realize magneto-optical waveguides with a non-reciprocal functionality such as TE-TM mode conversion.

Bulk glasses of the Sn10Sb $_{20-x}$ Bix Se70 (0 $\leq $ x≤ 8) system were prepared by the conventional melt quenching technique. Thin films were prepared by the thermal evaporation technique on glass substrates. Appearance of some crystalline phases is observed from the X-ray diffractograms after heat treatment below the glass transition temperature for 1 h. Scanning electron microscopy studies also show the presence of microcrystalline phases in the amorphous matrix after annealing for 1 h. The effect of Bi concentration and heat treatment on the optical gap and activation energy for dark conductivity were also investigated for the pristine as well as annealed films. The results are discussed on the basis of models related to the presence of defect states in chalcogenide materials.

Tin sulphide films have been deposited onto glass substrates at room temperature by chemical bath deposition using aqueous solution. The structural and vibrational properties of the deposited films have been characterized by X-ray diffraction (XRD), FT-IR and Raman spectroscopy. XRD data indicate that as grown film is polycrystalline in nature and is composed of predominantly orthorhombic phase. Infrared spectrum of the film has been investigated in 4000–400 cm−1 region. The infrared spectrum of SnS displays several bands. The Raman spectrum studies revealed three peaks (64, 106 and 239 cm-1) of SnS film. The spectrum analysis also shows that there exists a Sn2S3or/and SnS2 phase in the deposited film.

Zinc potassium phosphate hexahydrate (ZnKPO4.6H2O) (abbreviated as ZPPH) single crystal is grown by reacting Potassium dihydrogen phosphate with Zinc Sulphate in equimolar ratio by slow evaporation. This compound crystallizes in the acentric orthorhombic symmetry class (space group Pmn21) and possesses photo induced optical second harmonic generation. The laser induced surface damage threshold for the grown crystal was measured as 1.7 × 1012 mJ/cm2 with Nd:YAG laser assembly which is of the same order as that of the reference KDP used in our experiment. The temperature dependent second harmonic generation studies were also carried out from room temperature to liquid helium temperature and the anomalies at low temperature qualifies this material as efficient low temperature optical switchers.

We investigated the pulsed laser ablation of metallic (Al), semiconductor (Si), and wide bandgap dielectric (LiNbO3) targets in air at normal atmospheric conditions by using 4.5 ns pulses at 532 nm wavelength. We determined the dependence of the ablation rate on the pulse number and laser fluence. The number of consecutive laser pulses hitting the target on the same area was between 5 and 40, and the laser fluence was varied in the range of 10–250 J/cm2 by changing the irradiated area at the target surface. We find that the ablation rate of the three targets is approximately constant when the pulse number is smaller than 15. Further increase of the pulse number leads to a decrease of the ablation rate, the fastest decrease of the ablation rate with pulse number being observed for the dielectric target. The dependence of the ablation rate on the laser fluence indicates two different regimes. In the first regime, which is for values of the fluence smaller than the threshold value (~70 J/cm2 for Al, ~90 J/cm2 for Si, and ~180 J/cm2 for LiNbO3), the ablation rate increases approximately logarithmically with the fluence. In the second regime, characterized by values of the fluence greater than the threshold value, there is a steep increase of the ablation rate. This sudden jump of the ablation rate at the threshold fluence is due to the transition from normal vaporisation to phase explosion, and to the changes in the dimensionality of the plasma-plume hydrodynamics from one-dimensional to three-dimensional.

The present paper deals with the investigation of Argon ions – substrate interactions during film growth and their influence on sputtered hydrogenated amorphous silicon (a-Si:H) thin films structural properties. These interactions are characterized by mean of the calculation of the energy distribution of Ar ions striking the substrate and their striking force measurement in the case of Rf diode sputtering. The influence of the Ar ions bombardment on structural and physical properties of amorphous silicon thin properties is discussed. The ion bombardment affects the film growth processes and consequently, it causes films densification and evolution of film microstructure from amorphous state at low power towards a microcrystalline material with increasing the Rf power.

An electric network is constituted by generators providing power to various loads. The induction machine is the most common motor in the industrial applications because of its simplicity of construction, its reliability and its low cost. It allows the constant speed applications when it is directly supplied by the network and variable speed ones with the use of power converters. These speed drives induce important harmonic perturbations in the power system and in the motor side. In this context, we are interested by the frequential modelling of the induction machine in order to simulate the line current with its harmonic components. In order to use the induction machine models, it is necessary to identify their parameters and therefore realizing specific and sufficiently informative tests. Several tests of identification are presented in the literature; their differences and their relevance have not been discussed. This study deals with the realization and the comparison of several types of frequential tests (constant voltage, constant V/f, injection of DC current) for induction machine models identification. The comparison of the simulation results with the experimental measurements allows electing the most representative of the induction machine behaviour.

This paper presents an analytical approach to estimate the magnitude of a flux density component at a point located outside an AC machine. The study uses the concept of attenuation coefficients which are determined using several hypotheses. The developments consider the different media according to they are flowed by eddy currents or not. Then, the calculations are performed in each medium.

This paper deals with an original approach of the Switched Reluctance Machine (SRM) control for the purpose of reducing stator vibrations. Two combined approaches are studied in the aim of reducing the vibratory acceleration generated and thus the acoustic noise. The first one is based on a sinusoidal control of the magnetic phase current and the second one, on an optimal control of piezoelectric actuators (PZT) stuck on the SRM stator. The sinusoidal control of the magnetic phase current introduces properties on the vibratory acceleration distribution that are used to design an original actuator controller. Principles and viability of these combined vibration damping methods are deduced from theories and experiments.

We explore numerically the feasibility of enhancing the mixing capability of microchannels by employing the Weierstrass fractal function to generate a pattern of V-shaped ridges on the channel floor. Motivated by experimental limitations such as the finite resolution (~10 μm) associated with rapid prototyping through soft lithography techniques, we study the influence on the quality of mixing of having finite width ridges. The mixing capability of the designs studied is evaluated using an entropic measure and the designs are optimized with respect to: the distances between the ridges and the position range of their tip along the width of the channels. The results are evaluated with respect to the benchmarks established by the very successful staggered herring bone (SHB) design. We find that the use of a non periodic protocol to generate the geometry of the bottom surface of the microchannels can lead to consistently larger entropic mixing indices than in cyclic structures. Furthermore, since the optimization curves (mixing index vs. geometric parameters) are broader at the maximum for fractal microchannels than for their SHB counterparts, the microchannel designs using the Weierstrass fractal function are less sensitive to experimental uncertainties.

In this paper, we study the behavior of immune memory against antigenic mutation. Using a dynamic model proposed by one of the authors in a previous study (A. de Castro [Phys. J. Appl. Phys. 33, 147 (2006) and Simul. Mod. Pract. Theory. 15, 831 (2007)]), we have performed simulations of several inoculations, where in each virtual sample the viral population undergoes mutations. Our results suggest that the sustainability of the immunizations is dependent on viral variability and that the memory lifetimes are not random, what contradicts what was suggested by Tarlinton et al. [Curr. Opin. Immunol. 20, 162 (2008)]. We show that what may cause an apparent random behavior of the immune memory is the antigenic variability.