A review of transmission properties of two-dimensional plasmonic structures in the terahertz regime is presented. Resonant terahertz transmission was demonstrated in arrays of subwavelength holes patterned on both metals and semiconductors. The effects of hole shape, hole dimensions, dielectric function of metals, array film thickness, and a dielectric overlayer were investigated by the state-of-the-art terahertz spectroscopy modalities. Extraordinary terahertz transmission was demonstrated in arrays of subwavelength holes made even from Pb, a generally poor metal, and having optically thin thicknesses less than one-third of a skin depth. We also observed a direct transition of a surface plasmon resonance from a photonic crystal minimum in a photo-doped semiconductor array. According to the Fano model, transmission properties of such plasmonic arrays are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Plasmonic structures will find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, and integrated terahertz devices.

Using the density-functional theory (DFT) combining non-equilibrium Green's function (NEGF) technique, we have studied the electronic transport properties of (7,0)-(8,0), (8,0)-(9,0) and (8,0)-(10,0) single-walled carbon nanotube heterojunctions which contain a pentagon-heptagon (5/7) pair of defect, a pentagon-heptagon (5/7) pair of defect and a pentagon-hexagon-heptagon (5/6/7) topological defect, respectively. Our calculations indicate that the 5/6/7 defect has greater effect on the electronic transport properties than that of the isolated 5/7 defect because there exist three weakly localized states in (8,0)-(10,0) heterojunction while two in (7,0)-(8,0) heterojunction. Furthermore, there appears to be negative differential resistance (NDR) in the semiconductor-metal (8,0)-(9,0) heterojunction in small bias region due to the suppression of conduction channel.

The optical and electrical properties of the as-prepared and annealed Snx Sb20Se $_{80-x}$ (where x = 8, 10, 12, 13.5, 15, 16.5 and 18 at.%) thin films were studied. X-ray diffraction showed that all the as-prepared Sn-Sb-Se films were amorphous. Annealing the films at 473 K or above crystallized the films and the degree of crystallinity depended on the Sn content. The optical transmittance and reflectance were measured in the wavelength rang 200–2500 nm. The estimated optical band gap was found to decrease with increasing Sn content. A great difference in the optical constants values due to transformation from amorphous to crystalline phase structure of the films were found after annealing. This is advantageous for optical disk data storage applications. It was found that the resistivity decreases with increasing temperature for all the compositions indicating that these films have a semiconducting behavior with thermally activated conduction. The conduction in these films was suggested to be thermally assisted charge carrier movement in the extended states. Annealing the films caused a reduction in the room temperature resistivity by six order of magnitude. This was ascribed to the amorphous-crystalline transformation.

The optical properties of Zn doped GaP single crystals were investigated in the spectral range of 200–2500 nm. It was found that the spectral distributions of R, n, $\varepsilon_{1}$ reflect sharp structure due to valance conduction band transitions (E g , E 0, E 1 and E 2) having the energies 2.17, 2.706, 3.708 and 5.245 eV, respectively. The tested samples exhibit indirect allowed optical transition associated with two phonons of energies 24.5 and, 58.7 meV. The free carrier concentration was found to be 2.11 × 1018 cm−3. The oscillation energy E osc , dispersion energy E d , lattice dielectric constant $\varepsilon_{L}$ , and optical dielectric constant at infinite frequency $\varepsilon_{\infty}$ were, also, calculated and found to be the values 4.4 eV, 38 eV, 10.27 and 9.7, respectively.

The electrical characteristics of thermally evaporated Chloroindium phthalocyanine thin films (ClInPc) are studied. A number of parameters are evaluated on the basis of the theory of space-charge-limited conduction. ClInPc thin films are extremely stable, in terms of both resistance to chemical attack and thermally, no hysteretic was observed after temperature cycling between room temperature and 500 K. DC current-voltage and current-temperature characteristics were obtained for ClInPc in vacuum and on exposure to dry air (20% O2) in both the dark and under illumination with visible light. The conductivity data were analysed in the framework of band theory to elucidate information about the activation energy E ac , forbidden band gap $(E_c-E_v)$ , domain or acceptor energy levels ( $E_e, E_h$ ). In the present work we also examine the response of ClInPc to O2 and NO2 at different temperatures.

The characteristics of the gate capacitance at polysilicon thin-film transistors (poly-Si TFTs) based on terms of surface potential have been described and modeled in this paper. An explicit approximate relation for surface potential as a function of terminal voltages is developed. The theory is based on an assumed exponential distribution of trap states in the energy gap. Moreover, the model has been found to give an accurate description of the unique features of poly-Si TFTs, such as rapid increase of C gs in leakage region and C gd in kink region. The good agreement between simulated model results and experimental data confirms the accuracy and efficiency of this model.

Forward and reverse leakage currents in GaN/InGaN multi-quantum well light-emitting diodes (LEDs) are caused by reactive-ion etching (RIE) damages during device patterning. A method to recover the damaged surfaces, based on a chemical etch in KOH:ethylene-glycol is described. Leakage currents decrease of more than a factor of 10 and are completely suppressed in most of devices.

In this paper, we present a numerical modelling of a NPN SiGe heterojunction bipolar transistor (HBT) realized in an industrial 0.35 µm BiCMOS process, using our own software simulator “SIBIDIF”, taking into account some electrically active defects in the HBT device. The electric performances of this device can be penalized by the presence of defects inherent to the complex structure shrinking. For our devices, most of these relevant defects are located at the vertical interface between the spacers and the polysilicon emitter, due to the Reactive Ion Etching (RIE) process step. Nevertheless, their localization, as well as theirs effective density or their capture section, have an influence on the electric characteristics of the HBT's. As a check, we find some good agreement between our simulated results and some experimental ones. Our work is focused on the identification of defects responsible for the current fluctuations at the origin of low frequency noise or Random Telegraphic Signals in industrial submicronic BiCMOS technologies. Gummel characteristics are simulated in order to identify generation-recombination or trap assisted tunnelling process in the base current. We have shown that devices having an excess base current present random discrete fluctuations on the base current.

This paper reports the characterization of lithium tantalite (LiTaO3) thin films deposited by sol gel process. Thin films were deposited on (001) sapphire substrates by spin coating. In order to study the effect of annealing temperature on the structural and optical properties, the films were annealed at several heating temperatures, ranging from 600 to 750 °C. From X-ray diffraction measurements it is confirmed that LiTaO3 films are highly c-axis oriented, the line width and the intensity of the (006) peak are sensitive to the variation of the annealing temperature and the best results were found at 700 °C. From SEM pictures it is found that the grain size increases from 100 to 200 nm when the annealing temperature is increased to 700 °C. From the optical transmittance and absorbance measurements, the band gap energy was extrapolated at about 4.6 eV which closely agrees with the LiTaO3 bulk value. Fourier transform infrared (FTIR) reflectivity and Raman backscattering were used as two complementary experiments to probe the zone center optical phonons in the lithium tantalite thin films.

Based on the dielectric-continuum model, the expression of polarization eigenvector, the dispersion relations, and the electron-phonon interaction Fröhlich-like Hamiltonian for interface optical (IO) phonons in multilayer GaN/AlN spherical heterostructures are obtained. As an application of the theory, the dispersion relations and electron-phonon coupling function strengths of the IO phonons are calculated for four-layer GaN/AlN/GaN/AlN spherical heterostructures. The results show that the lower frequency phonons have a much greater contribution to the coupling function $\Gamma _l^{IO} (r)$ than higher frequency phonons.

In this paper, the FeSiBNbCu and FeSiBNbCu-Al coatings were synthesized using cold spray technique in order to produce ferromagnetic materials. Ultra-fine grain coatings are obtained using FINEMET nanostructured powders mixed with Aluminum. Various percentages of Aluminum characterized by its low hardness were taken in account. The obtaining coatings were formed of Aluminum matrix and randomly distribution of FINEMET particles. Indeed, magnetic measurements revealed a soft magnetic character for all the powders and the coatings. 25% of Al was considered as ideal to produce a homogenous coating with good soft magnetic properties.

Porous silicon layers (PSL) were fabricated by electrochemical etching and investigated by spectroscopic ellipsometry (SE) in the energy range 0.6−5 eV. Within the effective medium approximation (EMA) and through an optical model consisting of a mixture of void and crystalline silicon (cSi), we were able to determine the porosity (void concentration) and the thicknesses of the PSL. The PSL were divided into several sublayers in order to obtain the best agreement between measured and simulated spectra. Once the etching parameters have been controlled and by choosing the appropriate conditions, it was possible to design a distributed Bragg reflector (DBR) with a high reflectivity band centered at 800 nm. This DBR consists on stacks of alternate PSL having two different refractive indices.

A novel method, based on emission signal from the excitation transfer reaction: Ar*(3P2) + N2(X) $\to $ N2*(C 3 $\Pi_{u}$ ) + Ar, is proposed for the intensity calibration of the spectroscopic optical detection system in absolute scale. It is applied for the measurement of N(2P°) metastable atoms density in the Short Lived Afterglow (SLA) of a 440 Pa nitrogen discharge produced by a 433 MHz resonant cavity. This density is deduced from the absolute intensity of the forbidden N(2P°–4S°) line at 346.65 nm, whose transition probability is only 0.005 s−1. The N(2P°) density variation in the SLA resembles those of N2(A 3 $\Sigma_{u}$ ) metastable molecules and electrons or the emission intensities of first positive (1+), second positive (2+) and first negative (1−) systems of N2. It first decays after the discharge zone up to a minimum and hence increases by almost a factor of thirty to reach a maximum value of 6 × 1017 m−3 at the maximum of the SLA. It is proposed that N(2P°) density results from a local equilibrium between its production: N2(A 3 $\Sigma _{u}^{+}$ ) + N(4S) $\to $ N(2P) + N2(X 1 $\Sigma _{g}^{+}$ , v) and loss: N2(X 1 $\Sigma _{g}^{+}$ , v≥ 10)+ N(2P) $\to $ N2 (A 3 $\Sigma _{u}^{+}$ ) + N(4S) reactions, which strongly couple the atomic and molecular metastable states and hence recycle N2(A 3 $\Sigma _{u}$ ) metastable molecules produced in the SLA. The balance equation of N(2P°) density provides a N2(X 1 $\Sigma _{g}$ ; v≥ 10) density of 6.5 × 1020 m−3 at the maximum of the SLA. This corresponds to 1% of the total N2 molecules in vibrationally excited levels v≥ 10.

Electrostatic filtration is a process that has been studied for more than a century. One of the most recent applications is Diesel exhaust gas aftertreatment. More specifically, car manufacturers are very interested in using electrical discharge phenomena to remove the soot particles from exhaust gases. This process could be a feasible alternative to the Diesel particulate filter used at the present time.The aim of this paper is to investigate the effects of repetitive voltage impulses on the treatment efficiency on soot particles and to compare results with those achieved when a DC supply is used. The study was divided into two steps: in the first, a study of the modes of discharge which develop in an electrostatic precipitator allows us to optimize both the geometry of an ESP and a hybrid pulsed power/direct voltage supply. This study was performed without gas flow. In the second step, investigations concerning treatment efficiency were carried out under practical conditions using an engine test bench. Results show that the combination of direct voltage (–7 kV) and pulsed voltage (–14 kV, 3 kHz) provides treatment efficiency close to 75% using electrical power three times lower than that required using a DC supply.

Composition of the applied shielding gas has a strong influence onphysical properties of the plasma and parameters of the weldingprocess. In particular, increase of the percentage of carbondioxide in argon results in an increase of the transition currentvalue while changing from the globular to spray mode of metaltransfer during the welding process. In order to explain thisphenomenon, the MIG/MAG welding arc plasma was investigated fordifferent mixtures of argon and carbon dioxide in the shieldinggas. Applying a fast camera, recording distribution of spectrallines of the plasma components, we noticed some phenomena notdescribed yet in the literature. Especially, there is a limit inthe percentage of relative concentration CO2/Ar beyond whichthe arc shape is significantly modified.

This paper describes implementation and initial evaluation ofvariable friction displays. We first analyse a device that comprises a stator of an ultrasonic motor supplied by onlyone channel. In this way, the stator does not induce any rotative movement butcreates a slippery feeling on the stator's surface. Considering the range of frequency and amplitude needed to obtain this phenomenon, weinterpret it as the squeeze film effect, which may be the dominant factor causing an impression of lubrication. This effect is thus able to decreasethe friction coefficient between the fingertip and the stator as a function of the vibration amplitude. Moreover, if we add a position sensor, we can create a textured surface by generating alternatively sliding and braking sensations by tuning the vibration amplitude of the wave.Then, based on the principle of the first device, another device isproposed in order to enable a free exploration of the surface, according to ergonomic requirements.