Measurements are presented of the magnetoelectric (ME) coupling of nontoxic lead-free multiferroic composites 0.4CoFe2O4-0.6[0.948(K0.5Na0.5)NbO3-0.052LiSbO3]. The composites are found to exhibit an interesting dielectric response under a dc magnetic bias field. The positive magnetodielectric behavior and its strong frequency dependence in the composite could be related to magnetoresistance and the Maxwell-Wagner effect. The ME effects are strongly dependent on the driving field frequency and dc magnetic bias field. The frequency and magnetic field dependence of direct and converse ME coefficients are related to the relative dielectric constant and the variation in the piezomagnetic coupling with magnetic field, respectively. In addition, the dependence of direct and converse ME coefficients on frequency and magnetic field is quite similar in this multiferroic particulate composite.

p-Type thin films of copper-strontium oxide (Cu-Sr-O) have been deposited by e-beam evaporation technique on microscopic glass substrates. A study of optical, electrical and structural properties was performed on the thin films, varying temperature of annealing. Amorphous Cu-Sr-O films were obtained at low temperature. Partially polycrystalline films were obtained at high temperature of 550 °C with transparency over 72% at wavelength from 600 to 700 nm in the visible region and 83% in the near infrared region (λ = 1800:2500 nm). The optical band gap was estimated to be ~3.5 eV. The Seebeck coefficient measurements showed that the as-deposited films represented n-type conduction and with annealing temperature these films converted to p-type. The electrical conductivity measurements at room temperature of annealed films at temperature of 550 °C represented the best value about 2 S/cm. The other optical parameters such as refractive index, extinction coefficient, dielectric constant and cutoff wavelength were studied as a function of annealing temperature.

We argue the possibility of realization of a polarization-insensitive all-optical switching in a planar metamaterial composed of a 4-fold periodic array of two concentric metal rings placed on a substrate of nonlinear material. It is demonstrated that a switching may be achieved between essentially different values of transmission near the resonant frequency of the high-quality-factor Fano-shape trapped-mode excitation.

Use of microorganism as a novel and eco-friendly strategy to production of nanomaterials is an important aspect of modern nanotechnology. Biosynthesis of quasi-spherical silver nanoparticles (Ag-NPs) has been investigated using Pseudomonas aeruginosa. We observe that silver (Ag+) ions when exposed to P. aeruginosa biomass are reduced in solution, thereby leading to the formation of Ag-NPs. Quasi-spherical shape and nearly well distribution and FCC crystal structure of Ag-NPs were confirmed by XRD pattern, STM and TEM micrographs. UV-Vis spectra show a surface plasmon resonance (SPR) band at ~ 435 nm.

In this paper we investigate and optimize the design of an OR gate all optical circuit based on silicon photonic crystals. The OR gate is formed by two ring resonators placed between three waveguides, obtained by removing specific rods from the photonic-crystal structure. To optimize the design parameters, the fill factor (r/a), corresponding to the ratio between the rod radius “r”’ and the inter-rod lattice “a’’, was varied using the plane wave expansion method. The Q-factor has been determined to achieve the optimal performance of the ring resonators. The optical properties and the normalized transmission spectra for the proposed gate based on the photonic-crystal ring resonators have been calculated by the finite difference time domain (FDTD) technique. We have noted that the two rings must be symmetric to the central waveguide to obtain the OR gate function in the output.

A novel characterization method using artificial neural networks is presented. This method allows one to determine the intrinsic permeability tensor of ferrite thin-films from S-parameters measurements. Neural networks, efficient to solve inverse problems, are used to compute the permeability tensor components μ and k. This optimization technique is used to find extremely complex functions between inputs and outputs and can be successfully applied on our magnetic thin-film characterization problem. Results of our networks are compared to a theoretical model. A great number of both simulated and measured tests have been performed on many magnetic thin-films. Neural network processing leads to a rapid and robust method for predicting the magnetic characterization of thin-films in microwave range.

Nanocrystalline La0.85Na0.15MnO3 ceramics were prepared via a novel method based on chemical solution combustion. Effects of sintering temperature on electrical transport and magnetic properties were systematically investigated. It was found that the resistivity increases, the magnetization decreases, and the metal-insulator transition temperature shifts toward low temperatures with the decrease of the sintering temperature. In addition, the magnetization of the samples sintered at low temperatures exhibits a broadened paramagnetic-to-ferromagnetic transition temperature. The low field magnetoresistance evidently increases with decreasing the sintering temperature due to the spin-polarized intergranular tunneling.

This work concerns the assessment of the surface temperature of copper anodes submitted to an electric arc in a non-stationary regime in air at atmospheric pressure. An infrared camera is used to measure the decrease of the surface temperature just after a very fast controlled arc extinction. Results are presented for different mean values of the arc current intensity (30, 70 and 130 A) with an electric arc duration in the range of 2–5 ms. The temperature decrease after the arc extinction allows an assessment of the surface temperature just at the moment of the arc switching off. In the present experimental conditions the mean temperatures reached for copper anodes are in the range of 750–1200 °C according to the arc current intensity values. Comparison between experimental results and a numerical modeling of the electrode heating allowed one to assess the surface power balance. The values for the volt equivalent are found about 12 V and the values for the surface power density are found to be near 2 × 109 W/m2.

This paper deals with the experimental characterization of discharges propagating over insulators of epoxy and glass, immersed in a gas or a gaseous mixture, under lightning impulse voltages (1.2/50 μs), using a point-plane electrode arrangement. The gases and mixtures we considered are SF6, N2, CO2, SF6-N2 and SF6-CO2. The morphology of creeping discharges and their final lengths are investigated versus the kind of insulator material, the amplitude and polarity of the voltage, the type of the gas (resp. mixture) and its pressure. It is shown that the shape of discharges and their final (stopping) lengths Lf depend significantly on the solid insulator and the type of gas. For given solid and gas, Lf increases quasi-linearly with the voltage and decreases when the gas pressure increases. The discharges do not always present a radial structure as reported in the literature. For given voltage and pressure, Lf is longer when the point electrode is positive than when it is negative while the initiation voltage of discharges is higher with a negative point than with a positive one; and Lf is longer with glass than with epoxy. Lf is shorter in SF6 than in CO2 or N2. On the other hand, the increase of SF6 content in SF6-CO2 mixture leads to a significant decrease of Lf. Therefore, the addition of small concentration of SF6 in a given gas mixture improves the dielectric strength of insulating structure.

This paper deals with new neural networks based harmonics detection approaches to minimize hardware resources needed for FPGA implementation. A simple type of neural network called Adaline is used to build an intelligent Active Power Filter control unit for harmonics current elimination and reactive power compensation. For this purpose, two different approaches called Improved Three-Monophase (ITM) and Two-Phase Flow (TPF) methods are proposed. The ITM method corresponds to a simplified structure of the three-monophase method whereas the TPF method derives from the Synchronous Reference Frame method. Indeed, for both proposed methods, only 50% of Adalines with regard to the original methods is used. The corresponding designs were implemented on a FPGA Stratix II platform through Altera DSP Builder® development tool. After analyzing those two methods with respect to performance and size criteria, a comparative study with the popular p-q and also the direct method is reported. From there, one can notice that the p-q is still the most powerful method for three-phase compensation but the TPF method is the fastest and the most compact in terms of size. An experimental result is shown to validate the feasibility of FPGA implementation of ANN-based harmonics extraction algorithms.

Multi-band metamaterial absorber (MA) was proposed at the microwave frequency ranges, which were composed of cave-cross resonator (CCR) with different geometric dimensions, dielectric substrate and continuous metal film. Microwave experiments demonstrated the maximum absorptivity of single CCR structure to be about 99% around 9 GHz. Numerical simulations confirm that the MA could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. Importantly, numerical simulations demonstrate that the MA could achieve perfect multi-band absorption by assembling the multi-CCR structure with different geometric parameters in a coplanar.

The atomic and electronic properties of the substitutional phosphorus (P) on the Si(1 1 1)-(2 × 1) surface have been studied by using the ab initio density functional theory (DFT) based on pseudopotential approach. We have considered four different possible binding sites for P adatom in the π-bonded chain labeled sites 1–4 respectively in Figure 1. We have found that the site 1 position in the π-bonded chain was energetically more favorable than the other binding sites, by about 0.1 eV/adatom. We have also calculated the corresponding surface electronic band structure and found one surface state, labeled C, in the fundamental band gap of Si(1 1 1)-(2 × 1) surface. Our calculations show that the P/Si(1 1 1)-(2 × 1) surface has a metallic character in the nature. In order to explain the nature of this surface state in the bonding geometry, we have depicted the total and partial charge density contours plots at the J¯$ \bar{J}$ point of the surface Brillouin zone (SBZ).

Electrodes and the nature of their contact with organic materials play a crucial role in the realization of efficient optoelectronic components. Whether the injection (organic light-emitting diodes – OLEDs) or collection (organic photovoltaic cells – OPV cells) of carriers, contacts must be as efficient as possible. To do this, it is customary to refer to electrode surface treatment and/or using a buffer layer all things to optimize the contact. Efficiency of organic photovoltaic cells based on organic electron donor/organic electron acceptor junctions can be strongly improved when the transparent conductive anode is coated with a buffer layer (ABL). We show that an ultra-thin gold (0.5 nm) or a thin molybdenum oxide (3–5 nm) can be used as efficient ABL. However, the effects of these ABL depend on the highest occupied molecular orbital (HOMO) of different electron donors of the OPV cells. The results indicate that, in the case of metal ABL, a good matching between the work function of the anode and the highest occupied molecular orbital of the donor material is the major factor limiting the hole transfer efficiency. Indeed, gold is efficient as ABL only when the HOMO of the organic donor is close to its work function ФAu. MoO3 has a wider field of application as ABL than gold. The role of the oxide is not so clearly understood than that of Au, different models proposed to interpret the experimental results are discussed.

This article describes a new principle of transduction involving an heterojunction between a Molecular Semiconductor and a Doped Insulator (MSDI). Herein, we report on an MSDI-based sensor featuring an heterojunction between a lutetium bisphthalocyanine (LuPc2), which acts as Molecular Semiconductor (MS) and a thin film of Doped Insulator (DI) made of substituted or fluorinated copper phthalocyanine (CuFnPc, where n = 0, 8, 16). Previously, we reported the peculiar effect of the heterojunction on the MSDI’s electronic behavior, suggesting this device as a new kind of transducer for gas chemosensing. Indeed, of particular significance was the key role of modulator played by the nature of the doped insulator sub-layer. While the MS thin film remains the only layer of the sensor exposed to gas atmosphere, the DI’s ability to tune the electronic characteristics of the organic heterojunction allows it to drastically affect the nature of the effective charge carriers. In particular, an increase in fluorination of the doped insulator can cause an inversion of the LuPc2 response toward electron accepting (ozone, ppb level) or donating (ammonia, ppm level) gases. The present work focuses on the structural, electronic and electrical properties of the MSDI heterojunction, which have been studied by UV-vis spectroscopy, atomic force microscopy, current-voltage measurements and chemical doping, in order to shed some light on this phenomenon. The unique ambipolar nature of LuPc2 is suggested to be the main property responsible for the MSDI’s unique behavior.

We report on the effects of continuous UV-visible light illumination at 60 °C in the absence of oxygen on P3HT:PCBM blend films commonly used active layer of bulk heterojunction solar cells. A full description of the behavior of P3HT:PCBM blend films either unconfined or confined by an Al cathode and a PEDOT:PSS layer during annealing treatment and irradiation is provided. We also focused on the impact of the P3HT type on the photostability. It was shown that the microstructure of P3HT dramatically influenced the photodegradation process of P3HT thin films deposited on inert substrate. The rate of photodegradation process was decreased when P3HT was blended with PCBM. It was shown that the photostability of the active layer was not influenced by a PEDOT-PSS sub-layer. Solar cells were then fabricated from high-regioregular P3HT. Many large PCBM crystals were observed in P3HT:PCBM blend films and it was shown that the top surface of the active layer in contact with the Al cathode was nearly entirely composed of P3HT. Both results account for the low performances of the devices. Finally, photo-aging experiments provoked a rapid failure of the Al cathodes which was tentatively attributed to an increase of internal strain within the devices.

Organic metal-semiconductor field-effect transistors (OMESFETs) were fabricated with a polycrystalline organic semiconductor (pentacene) and characterized in order to systematically analyze their operation mechanism. Impedance measurements confirmed full depletion of the thick pentacene film (1 μm) due to the low doping concentration of unintentional doping (typically less than 1014 cm−3). The necessity of developing a specific device model for OMESFET is emphasized as the classical (inorganic) MESFET theory based on the depletion modulation is not applicable to a fully-depleted organic semiconductor. By means of joint electrical measurements and numerical simulation, it is pointed out that the gate voltage controls the bulk distribution of injected carriers, so that the competition between the gate and drain currents is critical for determining the operation mode. Finally, the geometrical effect is investigated with comparing a number of transistors with various channel widths and lengths.

The effect of OTS (octadecyltrichlorosilane) Self-Assembled Monolayer (SAM) grafted on SiO2 gate dielectric of pentacene-based OFETs (organic field-effect transistors) is investigated. A significant improvement of the charge mobility (μ), up to 0.74 cm2/V s, is reached thanks to OTS treatment. However, in spite of improved performances, several drawbacks, such as an increase in mobility dispersion, substantial hysteresis in IDS-VG characteristics and high threshold voltages (VT), are observed. Changing solvent and deposition method turns out to have no significant effect on the mobility dispersion. A more accurate approach on the evolution of the mobility and the threshold voltage dispersion with OTS storage time highlights the effect of the OTS solution aging. Even if no difference is evidenced in the surface energy and roughness of the OTS layer, electrical characteristics exhibit considerable deterioration with OTS solution storage time. Using an “aged” OTS solution, opened under air, kept under argon and distilled before use, results in an increase of the IDS-VG hysteresis as well as in VT and in mobility dispersion. In comparison, fresh-OTS-based OFETs present a very low hysteresis, a threshold voltage close to 0 and a much lower mobility dispersion. It is demonstrated that aged OTS solutions contain impurities that are not removed by distillation process, which leads to a less densely packed layer causing interfacial charge traps thus deteriorated performances.

The nanostructure of the active layer in polymer/fullerene bulk heterojunction solar cells is known to have a strong impact on the device performances. Controlling the polymer/fullerene blend morphology is therefore particularly important. In this work, a rod-coil block copolymer, based on a regioregular poly(3-hexylthiophene) electron-donor rod block and a C60-grafted coil block, is used as compatibilizer and its influences on the thin film morphology as well as the photovoltaic performances are investigated. It is shown that a small fraction of compatibilizer can enhance the device performances in an otherwise non-optimized process. At higher fractions or long annealing times however, the fullerene-grafted copolymer is found to behave as a nucleation center and triggers the formation of fullerene crystals.

In this paper we report a detailed study of emission dynamics of an organic solid-state laser structure so-called VECSOL standing for Vertical External-Cavity Surface-emitting Organic Laser recently developed in our group. An optical-optical efficiency of 43% and 6.3% was reported for a 4-mm-long cavity incorporating 18-μm-thick film of Poly(methyl methacrylate) (PMMA) doped with 1 wt.% of Rhodamine 640 when pumped with 7-ns-long and 0.5-ns-long pulses respectively. In order to understand the difference seen in lasing efficiency as a function of different parameters such as cavity length or pump pulse duration, Tang-Statz-deMars cavity rate equations are used to model the emission behavior in a pulsed regime. Based on this model, conversion efficiency could be optimized practically to values as high as 57%. Furthermore, some characteristics of this laser architecture such as lasing lifetime (up to 140 000 pulses at two times above lasing threshold), wavelength tuning (over 40 nm) and the system power scalability with potential operation up to mJ level are investigated.