Superparamagnetic nanoparticles are widely used as contrast agents for magnetic resonance imaging. We present the Proton Nuclear Magnetic Resonance Dispersion curves for colloidal suspension of iron oxide nanoparticles used as contrast agents.The systems studied are composed of iron oxide nanoparticles of two different sizes, 80–150 nm dextran coated and 300–400 nm silicon coated.Previous studies show that the longitudinal relaxation time dispersion as a function of the proton Larmor frequency is not easily obtained for the aqueous colloidal suspension of 300–400 nm diameter nanoparticles. We obtained this system longitudinal relaxation time dispersion over a broad range of magnetic fields in a viscous medium. A theoretical model that accounts for the relaxation rate of water protons under the influence of such colloidal superparamagnetic nanoparticles was fitted to the experimental data of both systems.The fit allows access to characteristic parameters of superparamagnetic nanoparticles such as the Néel relaxation time, the nanoparticle radius, particle's magnetic moment and translational correlation time, important parameters for the contrast agent efficiency.

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.

The purpose of this paper is to review some elasticity effects in epitaxial growth. We start by a description of the main ingredients needed to describe elasticity effects (elastic interactions, surface stress, bulk and surface elasticity, thermodynamics of stressed solids). Then we describe how bulk and surface elasticity affect growth mode and surface morphology by means of stress-driven instabilities. At last stress-strain evolution during crystal growth is reported.

Transparent Yb3+-Er3+-Tm3+ co-doped nano-glass-ceramics have been prepared, 32(SiO2) 9(AlO1.5) 31.5(CdF2) 18.5(PbF2) 5.5(ZnF2): 3.5(Yb-Er-TmF3) mol%, where the co-dopants partition mostly to the fluoride PbF2-based nano-crystals. A comparative study of the up-conversion luminescence in nano-glass-ceramics and its precursor glass indicates that these materials can be used as blue/green/red tuneable up-conversion phosphor, in particular for white light generation. A ratio between blue, green and red emission bands of the Tm3+ and Er3+ can be widely varied with nano-ceramming of the precursor glass and with changing a pump power of luminescence. The change in the ratio between the blue, green and red emission bands is explained to be due to substantial lowering phonon energy and shortening of inter-dopant distances with nano-ceramming of the precursor glass and due to change in the ratio of 2- and 3-photon up-conversion processes with pump power.

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.

We present an overview of the possibilities offered by the combination of plasma polymers deposition and nanopatterning by colloidal and electron beam lithography. It is shown that chemical and topographical patterns can be obtained on different substrates, with dimensions of the order of a few 100 nm. Two examples of applications of these nanostructures for protein adsorption studies are presented.

Most applications involving metallic nanoparticle labelling necessitate both fast imaging and local spectroscopy of individual beads. We present an imaging method based on a guided laser illumination associated to spatial modulation which allows the detection of gold particles down to 10 nm. Using an imaging spectrometer and white incoherent illumination, the same system delivers individual spectroscopy of several gold beads simultaneously, allowing a fast and selective discrimination between individual metal particles and aggregates or dust.

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.

Microstructure and properties of the surface alloys resulted from a pulsed liquid-phase mixing of metallic substrates with pre-deposited films were studied. As a tool for the liquid-phase mixing, a low-energy (~30 keV), high-current (~30 kA) pulsed (0.8–3 µs) electron beam of energy density ranging from 1 to 15 J cm−2 has been employed. Three immiscible systems (Ta/Fe; Al/Si/Al/Si/Al/Si/Al; Al/C/Al/C/Al) and two systems with different solid solubility of components (Cu/316 stainless steel; Zr/Ti/Ti-6Al-4V) were chosen for the surface alloying investigation.

This paper deals with fault tolerant multiphase electrical drives. The quality of the torque of a vector-controlled Permanent Magnet (PM) Synchronous Machine supplied by a multi-leg Voltage Source Inverter (VSI) is examined in normal operation and when one or two phases are open-circuited. It is then deduced that a seven-phase machine is a good compromise allowing high torque-to-volume density and easy control with smooth torque in fault operation. Experimental results confirm the predicted characteristics.

The paper presents the possibilities to evaluate the health of an electrical machine by analyzing its electromagnetic emissions. Different piece of information can be detected according to the frequency range. First of all, a monitoring system sensitive to the degradation of the turn-to-turn insulation quality of the stator winding is presented; it is based on high frequency electromagnetic emissions. The second part of the paper is based on the medium and low frequency emission analysis. It explains how to detect turn-to-turn short circuits in stator windings or in the excitation coils of synchronous machines.

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.

Surface treatment of polymer films is usually necessary to improve surface wetting and adhesion characteristics. Traditional liquid chemical processes have several disadvantages in contrast to dry finishing processes, like plasma technology. Dielectric barrier discharges at atmospheric pressure are extensively studied for surface treatment, however, almost no research has been done on surface treatment with a dielectric barrier discharge at medium pressure. Therefore, in this paper, a polypropylene (PP) film is plasma-treated with a dielectric barrier discharge (DBD) in nitrogen at medium pressure (5.0 kPa). The surface properties of the plasma-treated samples are examined using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that the surface wettability is significantly enhanced after plasma treatment. The incorporation of nitrogen on the surface is significant (10 at%), demonstrating the ability of the used DBD set-up to generate nitrogen-containing functional groups on the PP surface. Nevertheless, a considerable amount of oxygen (10 at%) is incorporated onto the PP surface underlining the extreme reactivity of oxygen active species and the difficulty in overcoming the air contamination problem. Moreover, AFM analysis reveals that the nitrogen plasma creates large changes in the surface morphology of the PP film due to the selective etching of the amorphous regions of the polymer film.

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.

GaN epilayers were grown by metal-organic vapor phase epitaxy (MOVPE) on z- and x-cut lithium niobate substrates. Ex-situ characterizations of the epilayers by means of scanning electron microscope, atomic force microscope, X-ray diffraction and micro-Raman scattering measurements have revealed same growth features on both substrates. The observation of the morphology shows homogeneous and relatively smooth surface. The shape and density of GaN islands as well as the observed columnar growth mode are not dependent of the orientation of the LN substrates. The X-ray diffraction analysis of 450 nm thick GaN layers grown at 730 °C on z- and x-cuts showed that both GaN layers reveal the same crystallographic orientation, i.e. c-axis orientation normal to the substrate plane and in-plane orientation that coincides with the primary axis of LN substrates. The Raman scattering measurements confirm the growth of an oriented epitaxial GaN layer on LN substrate. Moreover, the deposited layer exhibit a quite good homogeneity, since the Raman spectra recorded for different positions in the layer do not reveal any significant variations in their relative intensities and frequency shifts.

A considerable number of communities throughout the world, most of them isolated, need hybrid energy solutions either for rural electrification or for the reduction of diesel use. Despite several research projects and demonstrations which have been conducted in recent years, wind-diesel technology remains complex and much too costly. Induction generators are the most robust and common for wind energy systems but this option is a serious challenge for electrical regulation. When a wind turbine is used in an off-grid configuration, either continuously or intermittently, precise and robust regulation is difficult to attain. The voltage parameter regulation option, as was experienced at several remote sites (on islands and in the arctic for example), is a safe, reliable and relatively simple technology, but does not optimize the wave quality and creates instabilities. These difficulties are due to the fact that no theory is available to describe the system, due to the inverse nature of the problem. In order to address and solve the problem of the unstable operation of this wind turbine generator, an innovative approach is described, based on a different induction generator single phase equivalent circuit.

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.

The increasing diffusion of power electronics in the electrical equipment induces harmonic perturbations which reduce the power quality of power systems. Moreover, the induction machine is widespread in the industrial applications and it is often supplied by speed drives which generate non sinusoidal voltages. In this context, this study deals with the frequential modelling of the induction machine in order to simulate the line current with its harmonic components. Some of the frequential models existing in the literature are presented and compared. Then a circuit model of the machine based on the superposition principle, an harmonic model, is proposed. The comparison of the simulation results with the experimental measurements allows electing the harmonic model associated to the identification test using a DC current as the most representative of the machine behaviour.