Differential scanning calorimetric (DSC) and X-ray diffraction (XRD) measurements on Sn-Sb-Se glassy semiconductors have been performed. Phase separation has been revealed with the broadening of the exothermic peak for 11 at% of Sn. The X-ray diffraction studies of annealed samples show that the investigated system could be treated as a solid solution of Sb2Se3 and SnSe2 phases. The deconvolution procedure was used to investigate the crystallization mechanism for the broad exothermic peaks in the thermal scans. From the heating rate dependence of the crystallization temperature, the crystallization parameters have been determined using Kissinger equation and Matusita equation. The investigated parameters indicate higher thermal stability and glass forming ability of Sn10Sb20Se70 chalcogenide glass.

In this paper, we report the experimental data of photoresponse namely; voltage responsivity and speed of response at λ = 904 nm of silicon photodiode formed by pulsed laser-induced diffusion technique. Experimental results demonstrated that the photodiode parameters strongly depend on the laser energy and substrate temperature. Maximum Responsivity obtained for p-n junctions photodetectors prepared by laser fluence of 9.17 J/cm2 for Al-doped Si and 10.03 J/cm2 for Sb-doped Si at substrate temperature (T s ) of 598 K. The pulse response waveform of photodetectors illustrated that the rise time is not dominated by RC. Non-linearity deviation coefficient was improved by factors 1.6 for and 2.7 for for Al-doped Si and Sb-doped Si photodetectors respectively when T s is raised from 300 K to 598 K.

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 V oc , the short circuit current density J sc , the fill factor FF and the efficiency) are compared and related to each other. One finding is that not the V oc , but the J sc 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 V oc . In recent literature, it is proposed that the V oc 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 V oc and the energy levels of donor and acceptor is searched from our empirical study.

This paper presents a review of some investigations that we have performed on electronically controlled EBG structures including their electromagnetic characterization and their applications for adaptive antenna. Firstly, for a structure composed of 2D cylindrical metallic wires array, an equivalent circuit approach is proposed based on a combination between the well-known Marcuvitz model and a distributed impedance per unit length model. The proposed method has allowed the determination of the S parameters for a 2D cylindrical metallic wires array loaded by active elements. The results when using this proposed approach show a good concordance with those obtained using other time consuming methods like a local field approach and the finite element method. Secondly a continuous electronic control for the radiation pattern of an adaptive antenna, using an Electromagnetic Band Gap structure having variable localized elements, is investigated. Rigorous electromagnetic simulations for this structure are carried out using integral equations techniques solved by the method of moments. Measurements of the realized radiating structure are in a very good agreement with simulated results.

The structural, electronic and optical properties of two principal representatives of spinel oxides CdGa2O4 and CdIn2O4 have been investigated using the full-potential augmented plane-wave plus local orbitals method within density functional theory. We used the generalized gradient approximation (GGA) for the exchange-correlation (XC) potential. Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for the band structure calculations. The equilibrium lattice constants and the internal parameters are in agreement with the available experimental results. Results obtained for band structure using GGA-EV show a significant improvement over other theoretical work and are closer to the experimental data. The pressure dependence of band gaps is investigated. The dielectric function, reflectivity spectra and refractive index are calculated up to 50 eV. Pressure and volume dependence of the static refractive index have been also calculated.

Crystallization processes of Se80Te20-x Cdx (x = 0, 4, 8, 10 and 12) alloys at different heating rates have been studied by differential scanning calorimeter (DSC) by using non-isothermal technique. The values of glass transition temperature (T g ) and crystallization temperature (T c ) are found to be composition and heating rate dependence. From the heating rate dependence of glass transition temperature and crystallization temperature, the activation energy of crystallization (ΔE c ), the activation energy for structural relaxation (ΔE t ) and the order parameter (n) have been calculated. It was observed that Se80Te16 Cd4 has a minimum value of activation energy of structural relaxation (ΔE t ), which indicates that this particular glass has a larger probability to jump to a state of lower configurational energy and higher stability in the glassy region.

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.

P-Aminoazobenzene (PAAB) is one of the 24 kinds of carcinogenic azo dyes that the European Union forbids but it does not yet have an official method to detect PAAB. This paper experimentally observes the Normal Raman Spectrum (NRS) and infrared absorption spectrum of PAAB and presents theoretical vibrational spectra calculated from a density functional theory (DFT) method on the basis of B3LYP with 6–31 basis set. The calculated results show very good agreement with the experimentally observed IR and Raman frequencies. We also report the SERS spectra of PAAB adsorbed on silver and copper layers, which offer a sensitive but simple method to detect PAAB. Finally, the possible adsorbed states of PAAB on the silver and copper layers are discussed.

Fluorine doped tin oxide (FTO) thin films have been prepared by spray pyrolysis technique with no further annealing. Films with 2.5% of fluorine grown at 400 °C present a single phase and exhibit a tetragonal structure with lattice parameters a = 4.687 Å and c = 3.160 Å. Scanning electron micrographs showed homogeneous surfaces with average grain size around 190 nm. The films are transparent in the visible zone and exhibit a high reflectance in the near infrared region. The best electrical resistivity was 6.3 × 10-4 Ω cm for FTO with 2.5% of fluorine. The ratio of transmittance in the visible to the sheet resistance are in the 0.57 × 10-2–1.96 × 10-2 Ω-1 range.

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.

We investigate the temperature dependence of photoluminescence (PL) properties of InAs/GaAs quantum dot (QD) heterostructures. The temperature dependence of the InAs exciton energy and linewidth is found to display a significant difference due to the different dot size distribution. We propose a model, which takes into account the dot size distribution, state filling effect, carrier thermal escaping and retrapping, and electron-phonon scattering, to explain the carriers transferring mechanisms in the QD system. The experimental results are reproduced well by our model. Sample with lower dot size uniformity reveals evident thermal redistribution effect among dots, but the effect is weak for sample with higher dot size uniformity and is overcome by the electron-phonon scattering, which is consistent with the observed monotonically increasing linewidth of PL spectra with temperature.

Charge retention properties of Ge nanoparticles embedded in SiO2 matrix are investigated. Formation of embedded Ge nanoparticles was accomplished by optimizing electron beam evaporation process. Size of Ge nanoparticles has been characterized by atomic force microscopy (AFM) which comes out to be ~15 nm. Presence of Ge nanoparticles is confirmed by micro-Raman analysis. Memory effect of Ge nanoparticles is verified by capacitance-voltage (C-V) measurements which show hysteresis in the C-V curves.

New configuration for generation of the parametric X-ray radiation (PXR) by an ultrarelativisticelectron 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 spectralintensity is calculated for this case. It is shown that this specific configuration of the electron beam andtarget radiator can be used for the PXR generation in a storage ring. It can allow one to obtain themonochromatic X-ray beams with the smoothly tuned frequency and the spectral intensity exceeding intensity of thesynchrotron radiation in the narrow spectral ranges.

Si-doped and undoped GaAs1-x Nx layers are grown by molecular beam epitaxy (MBE) on GaAs(001) substrate with low nitrogen content. The Si-doped effect has been analyzed by photoluminescence (PL) measurements. At low laser power excitation the PL spectra of undoped layer are formed by GaAsN band level and several features attributed to the nitrogen localized states. For Si-doped layer, the GaAs1-x Nx Nx band level disappears and the large band attributed to the nitrogen localized states changes the form. At high laser power excitation, the PL spectrum is formed by only one peak corresponding to the most dominating nitrogen localized state. By comparing the doped and undoped layers, we note that the presence of silicon in the structure reduce the exciton bound energy to the nitrogen localized states.

We report the characterization of 1,8-naphthalene benzimidazole comprising carboxyl group. We have fabricated dye-sensitized nanocrystalline TiO2 solar cell (DSSC) based on naphthalene benzimidazole dye. The device structure is FTO/nc-TiO2/Dye/I–/I3 –/Pt/ FTO. We calculated the E HOMO and E LUMO levels of this new dye by using cyclic voltammetry measurement. The E LUMO level of naphthalene benzimidazole is 3.2 eV. This value is higher than the conduction band of TiO2. Electrons can be injected to the conduction band of TiO2. The current-voltage (I-V) characteristic of cell was measured under simulated AM 1.5 illumination (100 mW/cm2). We obtained the open circuit voltage; V oc = 0.344 V, short circuit current density; I sc = 5.93 mA cm-2, filling factor; FF = 0.45, power conversion efficiency; η = 0.91%.

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.

PVPx V2O5 (x = 0, 0.5 and 1) nanobelts were obtained using a simple hydrothermal process from V2O5 xerogel. The structure and morphology of the samples were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The interaction between the poly (vinyl pyrrolidone) (PVP) and V2O5 xerogel in the nanocomposites was verified by Fourier transformation infrared spectroscopy (FTIR). The electrochemical cells, with a configuration Li/(LiPF6 + EC + DMC)/(V2O5 + PVP), were fabricated and their electrochemical performance was studied.

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.).

Tilt growth is usually observed for the thin film growth on a substrate. Such tilt growth is considered as a consequence of the relaxation of the misfit strain between the epilayer and the substrate. In this paper, we propose a theoretical method to obtain the tilt angle of the epilayer, especially suitable for the heterostructure with large misfit strain which can be more than 10%. As an application of our method, we focus on two growth cases. One case is the growth of MnAs epilayer on GaAs (113) substrate with the lattice mismatch between the MnAs epilayer and the GaAs (113) substrate as high as 80%. And the other case is the growth of GaN epilayers on GaAs $\{1 \overline 1 l\}$ substrates. Results calculated from our method for the two cases agree well with the experimental observations. This method is general, and can be applied to other material systems with large lattice mismatch.