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.

With the purpose to increase the light confinement and the efficiency of silicon solar cells, the reflection of the surface emitter needs to be minimized and the minority carrier collection improved. This improvement is currently achieved by the application of the chemical vapor etching (CVE) technique. In this paper, we investigate the effects of CVE on surface texturing and silicon grooving. CVE-based porous silicon (PS) was found to be a good antireflection and passivation layer for multicrystalline Si (mc-Si) solar cells. As a result, the reflectivity of the mc-Si solar cell decreases by about 60% of its initial value in the 650–950 nm spectral range and the internal quantum efficiency improves by 30% after PS application in the 400–700 nm spectral range. CVE can be used for surface texturing of single or mc-Si Si wafer leading to lower surface reflectivity and reduction of the dead layer. The chemical vapor etching techniques enabled realize buried metallic contacts by grooving mc-Si silicon wafers. The spectral response of mc-Si solar cells was found to enhance of about 12% in the long wavelength range when a rear buried metallic contacts is achieved, while a significant increase of about 35% was observed at short wavelengths (400–650 nm spectral range) subsequent front grid buried metallic contacts realization.

Double-channeled omnidirectional filtering properties are found in the sandwich structure composed of a ε-negative layer and a μ-negative layer separated by another single-negative layer with either dielectric permittivity or magnetic permeability described by Lorentz model. The twin tunneling interface modes are generated by the excitation of surface polaritons. It is shown that the two tunneling modes are insensitive to the incidence angles and the polarizations. Furthermore, the tunneling frequency and the frequency interval of the two modes can be tuned by changing the resonance frequency and the thickness of the center layer respectively. The characteristics can be utilized to design double-channeled tunable omnidirectional filters using in microwave and optical engineering.

Dielectric barrier surface discharges (DBD) have the potential to act as flush mounted flow control devices for separation control and other aeronautic applications. A pulse-sustained plasma with the ions driven by a DC bias voltage is proposed for optimum performance. While characterizing these devices, it was found that their performance is severely limited by surface charge build-up. That charge builds up rapidly and remains for as long as hours. Work in this paper shows that the surface charge can be mitigated by using a reversing DC bias potential or by using a constant DC bias potential with a partially covered electrode.

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.

Dynamics of the controlled streamer-to-spark transition in atmospheric-pressure air is simulated. Results of calculation show that at proper selection of the parameters (the feeding capacitor, the ballast resistor) of power-supply electric circuit it is possible to produce non-thermal plasma filaments of radii about 10−2 cm, the mean gas temperature inside the filament being about 2000-3000 K and the electron number density being 1013–1014 cm−3.

Composite films containing silver nanoparticles embedded in diamond-like carbon (DLC) matrix were deposited on glass substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition techninique (CVD). Particle size and metal volume fraction were tailored by varying the relative amount of methane of a gas mixture of methane + argon in the plasma. Optical constants of the films were evaluated. Bonding environment in these films were obtained from Raman and FTIR studies. Blue-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was associated with the increase in volume fraction of metal particles. The experimental results have been discussed in light of the existing Mie theory.

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.

The paper highlights applications of some atmospheric pressure plasmas (dc-corona, streamer and spark and ac-Dielectric Barrier Discharges) to aerosol processes for Materials and Environment (filtration, diagnostics).The production of vapor i.e. condensable gaseous species, leads to nano-sized particles by physical and chemical routes of nucleation in these AP plasmas: (i) when dc streamer and spark filamentary discharges as well as ac filamentary dielectric barrier discharges interact with metal or dielectric surfaces, and (ii) when discharges induce reactions with gaseous precursors in volume. It is shown how composition, size and structure of primary nano-particles are related to plasma parameters (energy, number per unit surface and time and thermal gradients).Then the growth by coagulation controls the final size of agglomerates versus plasma parameters and transit time in and after the plasma. Charging and electro-thermal collection are depicted to account for the related potential applications of controlled kinematics of charged aerosol.

In this study the influence of morphology of vertically oriented titanium oxide nanotube arrays (TNTAs) on their photocatalytic activities was investigated. To obtain nanotubes with different morphologies, they were prepared at different anodization voltages. The size of TNTAs were measured using SEM images and also determined based on a non-destructive optical method; We demonstrate how the tubular geometry of the TNTAs can be used to adjust the optical and also the wetting properties of them and how these properties affect the performance of the nanostructure in further applications as a photocatalyst. To investigate their potentials for environmental applications, the photocatalytic activity of TNTAs in methylene blue (MB) aqueous solution was evaluated and compared to the behavior of porous TiO2 layers; we have found that the nanotubular TiO2 electrodes have considerably better photocatalytic performance in comparison with porous samples and the photocatalytic activity of TNTA was strongly dependent on the crystallographic structure and morphology.

This paper is a state of the art of the understanding on the physics of homogeneous dielectric barrier discharges at atmospheric pressure. It is based on the analysis of present and previous work about the behavior of these discharges and the conditions to get them. Mechanisms controlling the homogeneity during gas breakdown and discharge development are successively discussed. The breakdown has to be a Townsend one, the ionization has to be slow enough to avoid a large avalanche development. During the breakdown, the discharge homogeneity is related to the ratio of the secondary emission at the cathode (γ coefficient) on the ionization in the gas bulk (α coefficient). Higher is this ratio, higher is the pressure × gas gap product (Pd) value for which a Townsend breakdown is obtained. Among the phenomena enhancing the secondary emission there is the negative charge of the dielectric on the cathode surface, the trapping of ions in the gas and the existence of excited state having a long lifetime compared to the time between two consecutive discharges. The first phenomenon is always present when the electrodes are covered by a solid dielectric, the second one is related to the formation of a positive column and the third one is specific of the gas. During the discharge development, the homogeneity is mainly controlled by the voltage or the current imposed by the electrical circuit/electrode configuration and by the gas ability to be slowly ionized. Larger is the contribution of a multiple step ionization process like Penning ionization, higher will be the working domain of the discharge. A decrease of the gas voltage during the discharge development is a solution to enhance the contribution of this process. After 20 years of research a lot of mechanisms have been understood however there is still open questions like the nature of the Inhibited homogeneous DBD, surface energy transfers, role of attachment and detachment...

Nucleation of a gold catalyst on a (100) oriented silicon substrate was extensively investigated. An anomalous mechanism of nucleation was observed in the grain formation of gold nanoislands. The chemical vapour deposition method was employed to grow zinc oxide nanowires. Zinc powder and oxygen gas were used as reaction sources for the growth. Different shaped ZnO nanowires were obtained for different nucleation mechanisms. The nucleation mechanism and growth evolution were monitored by scanning electron microscopy and atomic force microscopy.

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.

The paper reviews a current state of the art in the in-line plasma treatment of low-cost materials and opportunities for the use of the so-called Diffuse Coplanar Surface Dielectric Barrier Discharge (DCSBD). A brief outline of physical mechanism and basic properties of DCSBD is given. The results presented on the ambient air plasma treatments of textile, paper, wood, and glass illustrate that DCSBD offers outstanding performance with extremely low energy consumption for large area, uniform surface modifications of materials under continuous process conditions.

We measured the single-photon detection efficiency of NbN superconducting single-photon detectors as a function of the polarization state of the incident light for different wavelengths in the range from 488 nm to 1550 nm. The polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good agreement with numerical calculations. We use an optical-impedance model to describe the absorption for polarization parallel to the wires of the detector. For the extremely lossy NbN material, the absorption can be kept constant by keeping the product of layer thickness and filling factor constant. As a consequence, the maximum possible absorption is independent of filling factor. By illuminating the detector through the substrate, an absorption efficiency of ~70% can be reached for a detector on Si or GaAs, without the need for an optical cavity.

The generation of singlet delta oxygen states (O2(a1Δg )) by microplasmas has been studied experimentally. In the present paper, it is shown that micro-cathode sustained discharges (MCSD's) can be used to produce high fluxes of O2(a1Δg ) at atmospheric pressure. In He/O2/NO mixtures, O2(a1Δg ) number densities higher than 1016 cm−3 can be generated by this 3-electrode configuration and transported over distances of some tens of cm. In fact, at total flow rates up to 30 ln/min, O2(a1Δg ) fluxes above 10 mmol/h were measured in the MCSD afterglow, at 26 cm downstream. As a result, MCSD's appear to be very efficient and suitable tools for the continuous production of large amounts of O2(a1Δg ) at atmospheric pressure, which could give rise to a wide range of new applications, namely biological. The effect of different parameters such as gas flows and mixtures, and discharge current are discussed in the paper.

Several important errors and misinterpretations present in a recent publication by Khan et al. [Eur. Phys. J. Appl. Phys. 45, 11002 (2009)] are pointed out and discussed. In particular, it is shown that the method used to calculate the rate coefficients for the electron impact excitation of 3p 54p and 3p 55p states of argon is incorrect and leads to unrealistically high rate coefficients.