As-grown ZnO thin films are annealed in O2 ambient for 15 min at the temperature of 700 °C, 800 °C, 900 °C and 1000 °C, respectively. Then the Ga2O3 thin films are deposited on ZnO/Si(111) substrates by sputtering Ga2O3 target in a JCK-500A radio frequency magnetron sputtering system. The low dimensional GaN nanostructured materials are obtained on Si substrates by ammoniating the Ga2O3/ZnO films at 950 °C for 15 min in a quartz tube. X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR) and photoluminescence (PL) are used to analyze the structure, morphology and optical properties of GaN nanostructured films. The results show that their properties are investigated particularly as a function of annealing temperature of ZnO layer. The mechanism is also briefly discussed.

We studied and compared the reported characteristics of 22 different bulk heterojunction organic solar cells fabricated and characterized by different research institutes. We only considered bulk heterojunction solar cells where both the acceptor (the n-type) and the donor (the p-type) are organic. All cells were characterized under illumination with the standard A.M. 1.5 spectrum and an intensity of 100 mW/cm2. The material properties (the highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) of donor and acceptor) and the device characteristics (the open circuit voltage Voc, the short circuit current density Jsc, the fill factor FF and the efficiency) are compared and related to each other. One finding is that not the Voc, but the Jsc is the limiting factor for obtaining a high efficiency with the current state of technology. Also an empirical threshold of 0.2 eV is found between the LUMO's of the donor and acceptor, necessary for exciton dissociation. There has long been a debate about the origin of the Voc. In recent literature, it is proposed that the Voc is not related with the work function difference of the contacts, but with the energy difference between the LUMO of the acceptor, and the HOMO of the donor (called `the interface bandgap'). A relation between the Voc and the energy levels of donor and acceptor is searched from our empirical study.

The electron field emission properties of different graphitic and diamond-like nanostructures films are compared. They are prepared in the same CVD chamber on SiO2/Si(100) and Si(100) flat surfaces, respectively. These nanostructures are thoroughly characterized by scanning electron emission (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Films of dense aligned carbon nanotubes by far display the lowest threshold fields around few V/$\mu $m and the largest emission currents. Carbon nanofibers, with platelet arrangement of the graphitic planes parallel to the substrate, exhibit higher emission thresholds around 10 V/$\mu $m. Diamond nanostructures, either modified through ammonia incorporation within the gas phase or not, exhibit the largest emission threshold around 25 V/$\mu $m. The high enhancement factors, deduced from the Fowler-Nordheim plots, can explain the low emission thresholds whereas limitations to the electron transport ever occur through different processes (i) surface modifications of the surface, as the transformation of the SiO2 barrier layer into SiNx in the presence of ammonia evidenced by XPS; (ii) different orientation of the graphitic basal planes relative to the direction of electron transport (carbon nanofiber) and (iii) presence of a graphitic nest at the interface of the carbon nanostructure and the substrate, observed when catalyst is deposited through mild evaporation.

Molecular dynamics simulations were performed to investigate CF3 continuously bombarding SiC surfaces with energies of 10, 50 and 100 eV at normal incidence and room temperature. In the simulation, the deposition yield of C and F atoms from CF3, the etching yield and rate of C and Si from the initial substrate, and the surface structure profile are discussed. Accompanying the saturation of F atoms from the incident CF3 molecules deposited on the surface, a balance between C removal from the substrate and C deposition from CF3 is established, while Si and C etching from the initial substrate reaches a steady state. The simulated results show that the etch rate of Si is more than that of C. A carbon-rich surface layer is observed which is in good agreement with experiments. In the F-containing reaction layer, SiF in SiFx species is dominant.

New configuration for generation of the parametric X-ray radiation (PXR) by an ultrarelativistic electron beam is considered. The beam propagates along the external surface of periodical multilayer structure (superlattice) while the photons are emitted under the condition of grazing incidence diffraction. PXR spectral intensity is calculated for this case. It is shown that this specific configuration of the electron beam and target radiator can be used for the PXR generation in a storage ring. It can allow one to obtain the monochromatic X-ray beams with the smoothly tuned frequency and the spectral intensity exceeding intensity of the synchrotron radiation in the narrow spectral ranges.

The effects of conventional scattering mechanisms on the electron Hall mobility in GaN are calculated and analysed. The ratios of the transport to quantum scattering time are also calculated and the ratio is evaluated in closed form without any fitting parameters. The common interpretation of the transport and quantum lifetime ratios by using the analytical equation solutions gives us dominant scattering mechanisms. It has been observed that the ratio is larger for dislocation scattering than for impurity scattering. These both results are compared and summarized that the Coulombic scattering from a charged dislocation core is more dominant than impurity scattering.

The aim of this article is to explore materials made of polymer-titanate composites for application towards the size reduction of high frequency electronic components. A study has therefore been done on the dielectric effect of composites made of an epoxy matrix loaded with a mixture of barium titanate and calcium titanate. The effects have been quantified according to volume fraction of load. Results obtained from time domain reflectometry have been compared to modelling predictions from the generalized Lichtenecker law. Low frequency analysis (in the range DC — 500 MHz) has also been performed throughout this work, and it has primarily concentrated on conductivity behaviour which may be attributed to the effects of a percolation process. The study has confirmed the validity of the ternary mixture law being applied in order to predict the electromagnetic behaviour of the composite material. This material family may therefore find use in microelectronic applications and in the miniaturization of circuit components (substrates, components, cavities, antennas, etc.).

In this study, the emission spectra of OH (A2Σ → X2Π, 0-0) and N2 (C3Πu → B3Πg) emitted from the high-voltage DC (direct-current) corona discharge of N2 and H2O mixture gas in a needle-plate reactor are successfully recorded at one atmosphere. The relative vibrational populations and the vibrational temperature of N2 (C, v') in negative DC corona discharge are determined. The effects of discharge voltage, input power and added oxygen on the relative populations of OH (A2Σ) radicals and N2 (C3Πu) molecules in negative DC corona discharge are investigated. It is found that the relative populations of OH (A2Σ) radicals and N2 (C3Πu) molecules increase with increasing the discharge voltage and the input power and decrease with increasing the added oxygen. The emission spectra produced by positive DC corona discharge are also studied for comparing with negative DC corona discharge. However, the emission spectrum of OH (A2Σ → X2Π, 0-0) is not obtained in positive DC corona discharge, only the emission spectrum of N2 (C3Πu → B3Πg) is observed. The effects of discharge voltage and input power on the relative populations of N2 (C3Πu) molecules in positive DC corona discharge are also investigated. The relative populations of N2 (C3Πu) molecules increase with increasing the discharge voltage and the input power. The main involved physicochemical processes have been discussed.

A cylindrical hollow cathode discharge is modelled by the solution of the Boltzmann equation and by particle-fluid (hybrid) simulation. While the latter technique provides a self-consistent solution for the problem, the Boltzmann method provides detailed information about the electron kinetics in the discharge over the whole energy range. The results obtained from the two methods are consistent with each other and show a fair agreement with previous experimental data thereby validating the modelling methods used.

An exact two-dimensional (2-D) analytical model (AM) of slotless permanent magnet (PM) machines in polar coordinates is used to determine the analytical equations of the air-gap flux density at no-load operation. The authors show that, for a radial magnetization, there is an optimal magnet thickness which permits to maximize the no-load flux density. In order to use easily and directly this optimal value during the design of surface mounted PM motors (SMPMM), the authors propose an original analytical expression of this maximum magnet thickness that have been obtained by interpolation of the values given by several analytical computations. This interpolation function could be applied to SMPMM having a parallel or radial magnetization direction.

We measure by fluorescence emission and absorption spectroscopy rotational and vibrational temperature of YO molecule issuing from a liquid drop of Y2O3 melted at the focus of a solar furnace. Far from the surface and at high pressure these measurements are consistent with the predictions from a fluid dynamic calculation and are believed to give an approximate temperature of the gas phase surrounding the sample. Close to the surface and at low pressure these measurements disagree with the expected surface temperature. This results from the existence of a Knudsen layer near the vaporizing surface that, in these conditions and at our spatial resolution, we can explore, revealing according the gas pressure, quasi equilibrium or non-equilibrium conditions.

The short-term stability of passive atomic frequency standards, especially in pulsed operation, is often limited by local oscillator noise via intermodulation effects. We present an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain clock where, under normal operating conditions, it is usually too small to observe. To achieve this, we deliberately degrade the phase stability of the microwave field interrogating the clock transition. We measure the frequency stability of the locked, commercial-grade local oscillator, for two modulation schemes of the microwave field: square-wave phase modulation and square-wave frequency modulation. We observe a degradation of the stability whose dependence with the modulation frequency reproduces the theoretical predictions for the intermodulation effect. In particular no observable degradation occurs when this frequency equals the Ramsey linewidth. Additionally we show that, without added phase noise, the frequency instability presently equal to 2×10-13 at 1 s, is limited by atomic shot-noise and therefore could be reduced were the atomic flux increased.

The phenomena resulting from interaction between ion beam and mammalian cell pose important problems for biological applications. Classic Bethe-Bloch theory utilizing attached V79 mammalian cell has been conducted in order to establish the stopping powers of the mammalian cell for several-MeV single-proton microbeam. Based on the biological structure of the mammalian cell, a physical model is proposed which presumes that the attached cell is simple MWM model. According to this model and Monte Carlo simulation, we studied the energy deposition and its ratio on the selected attached mammalian cell for MeV proton implantation.