Silver sulphide Ag2 S thin films have been prepared on pyrex glass substrates by the spray pyrolysis technique using silver acetate and thiourea as starting materials. The depositions were carried out in the range of substrate temperatures from 100 to 300 °C. Measurements of X-ray diffraction show that the deposited layers at 250 °C were well crystallized and oriented preferentially in the direction $(\bar{1}03)$. Films surfaces were analysed by contact Atomic Force Microscopy (AFM) in order to understand the effect of the deposited temperature on the surface structure. On the other hand, from transmission and reflection spectra, the band gap energy determined is about 1.14 eV. In the same way, an iterative method based on the optical reflectance and transmittance of Ag2S thin film prepared at 250 °C were used to obtain the refractive index and the extinction coefficient. Their values vary in the wavelength range 640-2200 nm from 2.38 to 2.81 and from 0.001 to 0.277 respectively.

This paper addresses a multiscale strategy for the prediction of anhysteretic magneto-elastic behavior and its application to the definition of a magneto-elastic constitutive law for Terfenol-D. The multiscale modeling is based on an energetic procedure at the single crystal scale. Localization and homogenization procedures are then applied to deduce the constitutive law of polycrystalline media from the behavior of the corresponding single crystal. The method is applied first to define the magneto-elastic behavior of single crystals, and the application to polycrystalline samples is then considered. Modeling results are compared to experimental data.

An electrical model for a dielectric barrier discharge (DBD) is proposed, with the aim of its application in power supply design process. An identification method, which finds the actual value of the parameters in a model, is presented. The specific modelling of a XeCl exciplex lamp is developed, along with the identification procedure of the parameters, using a sinusoidal and a pulsed experiment. Electrical representation of the model is done in two different simulators. The applicability of the identified model is proved with different experiments. Differences between experimental and simulated waveforms are minor, encouraging the use of the model in the construction of the converter for the DBD lamp.

SnS nanoparticle has been synthesized initially using SnCl2 · 2H2O and Na2S · XH2O, in the presence of TEA by precipitation method and XRD and FTIR techniques have been used for characterization of the sample. Powder X-ray diffraction studies revealed the particle size to be 48 nm and the pattern represents polycrystalline herzenbergite orthorhombic crystal structure of SnS. The FTIR result also confirmed the SnS at 2354 cm−1. Secondly SnS:Se thin films have been deposited on glass substrates by electron beam evaporation technique and the films were annealed at 100 °C and 200 °C for 1 h. The unannealed films are amorphous in nature and the annealed film shows that a sharp crystalline peak is due to SnS. Also a peak is shown at 2θ = 14.39°, which is due to characteristic peak of SnSe2, established by their XRD patterns. The band gap energy (Eg) was determined from transmission spectra and an optical band gap of Eg varies from 1.6 eV to 1.79 eV.

Absorption spectra, luminescence spectra and luminescence decay time are investigated for a borosilicate glass containing low 0.1 wt% Ce3+ and high 15 wt% Tb3+ concentrations, together with the time-resolved luminescence. A broad absorption band due to parity allowed f → d transition is observed for Ce3+. Sharp absorption bands are observed in 3100–1600 nm region which are due to the 7F6 → 7FJ (J = 0, 1, 2, 3, 4) transition of Tb3+, while much weak absorption bands due to the spin-forbidden 7F6 → 5DJ (J = 2, 3, 4), 5GJ (J = 3, 5, 6), 5LJ (J = 7, 8, 9, 10), 5HJ (J = 4, 5, 6), 5IJ (J = 7, 8) and 5FJ (J = 2, 4) transitions are observed in visible-UV region. By excitation with 266 nm laser line, two broad UV emission bands due to Ce3+ are observed at 360 and 390 nm besides the intense green emission bands due to the 5D4 → 7FJ (J = 6, 5, 4, 3) transition of Tb3+ and weak blue emission bands due to the 5D3 → 7FJ (J = 6, 5, 4, 3) transition. The decay time of the UV, blue and green emission is estimated to be 17 ns, 3.8 µs and 2.17 ms, respectively. The rise time of the green emission is about 4 µs after the Ce3+ emission and the Tb3+ blue emission. No rise time is observed for the latter emission.

In the present work, we have studied the effect of impurity position on energy levels, the donor binding energy and third harmonic generation of a pyramid and a cone like quantum dot. For this goal, we have calculated the energy levels, wave functions and binding energy using finite element method for various impurity positions. Our results show that the impurity location plays an important and considerable role in the electronic and optical properties in a pyramid and a cone like quantum dot. We found that the third harmonic generation and binding energy of both quantum dots have a maximum value at a special impurity position. The special impurity location is different for the two quantum dots. Also, we have deduced that the third harmonic generation of a cone like quantum dot is larger than a pyramid quantum dot for same volumes and heights.

Ion counting with an electron multiplier (EM) is necessary when sputtered ions are used for in situ and precise isotopic abundance measurements (10−4$(1\sigma)$) on small sample volume (about 100 μm3 for pure silicon). Measurements were performed on silicon samples bombarded with Cs+ ions by extracting negative secondary monatomic Si− ions. Pulse-height distributions (PHD) and isotopic ratios were used as diagnostic tools for repeatability studies. Repeatability could be greatly improved by determining the optimal position of the impact area on the conversion dynode and by addressing each isotopic beam properly focused on this area (adaptive optics). A simplified model based on Poisson's laws was developed to fit PHDs and allowed us to calculate quantum detection efficiencies versus thresholds. EM isotopic discriminations were determined with the resulting semiempirical algorithm so as to reconstruct the lost information and get data independent of threshold setting. To reach consistent results, quasi-simultaneous arrivals (QSA) on the conversion dynode had to be assumed and modelled using direct ionisation yields Si−/ Cs+ at different collection efficiencies. The QSA corrected data fitted well on the terrestrial isotopic fractionation line. Dead time uncertainties and possible emission non-linear isotopic fractionation processes were examined. PHDs from other elements and polyatomic ions were also discussed.

Hexagonal AlN thin films have been deposited by DC reactive magnetron sputtering at room temperature. For a first set of samples, sputtered AlN films were deposited on silicon Si (100) substrates. For a second set, AlN films were deposited on 200 nm (002) oriented AlN epitaxial layer obtained by Molecular Beam Epitaxy (MBE) on Si (111). X-ray Diffraction (XRD) and High Resolution Transmission Electron Microscopy (HRTEM) analysis of the synthesized films on Si (100) substrate have shown an amorphous phase close to the interface followed by a nano-crystalline layer exhibiting (100) and (002) orientations of the hexagonal AlN crystalline phase. Finally a relatively well crystallised layer with a single (002) orientation has been observed for the thickest films. This improvement of crystalline quality with film thickness has been consistent with a drastic decrease of the films stress from –1.2 GPa at 300 nm to no stress around 800 nm and even 0.3 GPa tensile stress for 1.5 μm thick film. This behaviour was different when epitaxial AlN was used as substrate. In fact, we have observed thanks to HRTEM images and Selected Area Electron Diffraction (SAED) patterns, that the AlN film deposited on such a substrate exhibits the same crystalline quality and have the same orientation as the AlN epitaxial layer during the first 500 nm of thickness. A further increase of film thickness has caused a decrease on the crystalline quality. The films became polycrystalline while preserving a (002) preferential orientation.

The rapid development of low-power consumption electronics and the possibility of harvesting energy from environmental sources can make totally autonomous wireless devices. Using piezoelectric materials to convert the mechanical energy into electrical energy for batteries of wireless devices in order to extend the lifetime is the focus in many researches in the recent years. It is important and efficient to improve the energy harvesting by designing an optimal interface between piezoelectric device and the load. In this paper, a self-powered piezoelectric energy harvesting device is proposed based on the velocity control synchronized switching harvesting on inductor technique (V–SSHI). Comparing to the standard full bridge rectifier technique, the synchronized switching harvesting on inductor (SSHI) technique can highly improve harvesting efficiency. However, in real applications when the energy harvesting device is associated with wireless sensor network (WSN), the SSHI technique needs to be implemented and requires being self-powered. The conventional technique to implement self-powered SSHI is to use bipolar transistors as voltage peak detector. In this paper, a new self-powered device is proposed, using velocity control to switch the MOSFET more accurately than in the conventional technique. The concept of design and the theoretical analysis are presented in detail. Experimental results are examined.

This research work involves the plasma treatment of polyethylene terephthalate fiber to improve performance of various ionic lubricating agents. To do this, polyester fabric was pre-scoured with detergent, treated with atmospheric-air plasma and then coated with anionic, cationic and nonionic emulsions. Chemical and physical properties of samples were investigated by the use of Fourier transform infrared spectroscopy (FTIR), bending lengths (BL), wrinkle recovery angles (WRA), fiber friction coefficient analysis (FFCA), moisture absorbency (MA), scanning electron microscopy (SEM) and reflectance spectroscopy (RS). Study on chemical properties of fibers revealed that the plasma pretreatment modifies the surface of fibers and increases the reactivity of substrate toward various ionic emulsions. Physical properties of textiles indicated that the combination of plasma and emulsion treatments on polyester can improve crease resistant, drapeability and water repellency due to uniform coating of various emulsions on surface of textiles.

Organic field-effect transistors (OFETs) usually operate in the accumulation mode, where the biasing of the gate induces the charging of the insulator-semiconductor interface; the bias is negative in the most common case of p-type semiconductors. We show here that the application of a positive gate bias leads to the formation of a depletion layer, and a subsequent decrease of the drain current. We develop an analytical model for this depletion mode of the OFET. It is shown that measurements in the depletion mode give access to parameters such as the doping level and the density of trap levels. The model is applied to data obtained on sexithiophene (6T) film and single crystal OFETs. A substantial amount of traps is found in unsubstituted 6T, whereas the dihexyl substituted 6T is practically trap free. 6T single crystals are characterized by a very low doping level, which can be related to their very high purity. The possible use of the depletion mode to increase the on-off current ratio of OFETs is discussed.

Hybrid concepts based on a nanoscale combination of organic and inorganic semiconductors are a promising way to enhance the cost efficiency of solar cells through a better use of the solar spectrum, a higher aspect ratio of the interface, and the good processability of polymers.A new type of solar cells has been investigated. It is based on a heterojunction between regio-regular poly(3-hexylthiophene) as an organic electron donor and silicon as an inorganic electron acceptor. In a first step towards nano-structured devices, cells made of flat thin films of these materials have been studied as a model case of the heterojunction.The materials were characterized through ellipsometry and absorption spectroscopy. The devices were studied by means of their spectral response and their I-V characteristics. By combining these results, the contribution of each layer and the mechanisms of photocurrent generation are explained.The best cells to-date show a power conversion efficiency of 1.6% under AM 1.5 illumination, with a V oc of 0.704 V and a J sc of 4.22 mA/cm2.

Neodymium-doped zinc oxide (NZO) thin films were deposited on glass substrates by spray pyrolysis technique. X-ray diffraction patterns have shown that both undoped and Nd-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [0 0 2] direction.

The effective doping concentration has been determined by Rutherford backscattering measurements showing that the neodymium is not incorporated easily into ZnO host matrix. The surface roughness was shown to increase with Nd doping. NZO films are highly transparent in the visible region. The lowest electrical resistivity value of about 4.0 10−2 Ω cm was obtained for 1% Nd effective doping.

A wide-angle broadband absorber which is realized by periodic structures containing graphene-based hyperbolic metamaterials (GHMM) and isotropic medium is theoretically investigated. The GHMM is composed of monolayer graphene and conventional dielectric, which the refractive index can be tuned by the chemical potential, the thickness of dielectric and phenomenological scattering rates, respectively. A periodic structure of GHMM can obtain a broadband absorption which is shown to absorb roughly 70% (relative bandwidth is larger than 45%) of all available electromagnetic wave in absorption bandwidth at normal incident angle. Compared with some previous designs, our proposed structure has a relative bandwidth over a broad frequency range in mid-infrared. This kind periodic structures offer additional opportunities to design novel optoelectronic devices.

We have built three optical frequency standards based on the two-photontransition of rubidium at 778 nm, and analysed their performance over a period of morethan three years. We discuss some systematic effects that could lead to the reproducibility we observe, and point out the possible improvements of the devices.We also examine the short and long term stabilities of the systems, and show that wehave reached their ultimate performances.

Amorphous thin films of Se100 − XSbX (X = 1, 5, 10, 15 and 20) were synthesized by flash evaporation of the premelt quenched bulk samples. The optical properties were investigated from spectrophotometric measurements in the UV-VIS-NIR spectral region using Swanepoel’s standard envelope method and related techniques. The optical band gap energy (Egopt) was evaluated from the Wemple-Didomenico (WDD) single oscillator model and Tauc’s extrapolation method in the region where the absorption coefficient, α ≥ 104 cm–1. The observed values of Egopt and oscillator energy Eo were found to decrease monotonously with increasing Sb additive. The complex dielectric constant (ε), Urbach energy (Eu), optical conductivity (σ), plasma frequency (ωp) and lattice dielectric constant (εL) were deduced for each alloy composition. The complex refractive index (n) fitted well to Sellmeier function which can allow extrapolation of n outside the measured spectral range. The observed changes in optical parameters with Sb content were explained on the basis of increased defect states and changes in cohesive energy indicators (average heat of atomization (Hs), mean coordination number 〈Z〉 and average single bond energy (Hs/〈Z〉).

We have studied the microstructure and morphology evolution in PbSe films chemically deposited on GaAs(100) substrates. The films consisted of a single phase of nanocrystalline rocksalt PbSe. The deposition temperature was found to be an important parameter which strongly influences the film morphology. A gradual transition to strong (111) texture was obtained with increasing deposition temperature, accompanied by a significant increase in crystallite size. Transmission electron microscopy (TEM) cross-sections showed two distinct regions. A layer of small, rounded crystals near the GaAs/PbSe interface above which a second region composed of columnar, $\langle$111$\rangle$ oriented crystallites was observed. High resolution TEM and Fourier analysis showed that the first layer of crystallites are in epitaxial registry with the GaAs substrate, in spite of the large (8%) lattice mismatch and the presence of a thin, amorphous interfacial layer.

Thin amorphous and polycrystalline tungsten oxide films have been prepared by Chemical Vapor Deposition (CVD) from metallorganic precursor − tungsten hexacarbonyl − at atmospheric pressure. The dependence of the composition and the structure of tungsten oxide films on the technological conditions has been investigated by XPS, XRD, DTA-TGA and Raman spectroscopy. As a result it has been established that: at high values of the flow-rates of the reaction gases amorphous films of very low density have been obtained; in the XPS spectra of the understoichiometric WO3−y (0 < y < 0.3) films besides W6+, also W5+ and W4+ stateshave been observed. First to observe in the Raman spectra of amorphous CVD-WO3 films is the band at ~ 950 cm−1,characteristic for terminalW6+ = O bonds in result of the presence of structural water. Theexistence of structural water in the amorphous material has been established by thermal analyze, also.

In this review, we report on the use of low pressure plasmas for elaboratingmaterials at the heart of solid polymer fuel cells (SPFC), especially electrodes and themembrane electrolyte. Electrodes are formed using plasma sputtering techniques while theion conducting membranes are built up using plasma polymerization. Fuel cell performance willbe improved by these approaches. The electrode catalyst profile is optimized whilemembrane working temperature is increased and methanol crossover is lowered compared to conventional PEM fuel cells.