Absorption Coefficients of GaN / AlxGa1 – xN Core-Shell Spherical Quantum Dot

The total absorption coefficient in spherical GaN/AlxGa1 – xN core-shell nanodots is theoretically investigated taking into account effective mass approximation. The influence of the nanosystem geometry upon the energy spectrum and transition energy δE associated to interlevel transitions is studied. We found that the energy transitions vary with the core-shell radius, and the peak position of the total absorption coefficient is greatly affected by changing of the shell radius. The possibility of tuning the resonant energies by using the geometric core shell effect of the spatial confinement can be useful in the optoelectronic devices applications. Also we observed that the magnitudes of the total absorption coefficient can be increased significatly compared traditional cases of QD, and the peaks are shifted to the lower energies. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2960

High Second-Order Nonlinear Susceptibility Induced in GaN/AlxGa1 – xN Coupled Quantum Well for Infrared Photodectors Application

The second harmonic generation (SHG) of GaAs/AlxGa1 − xAs a wurtzite coupled quantum wells (CQWs) is studied theoretically for different widths of well, barrier and values Al concentration, taking into account the strain-induced piezoelectric (PZ) effects. The analytical expression of the SHG susceptibility is deduced by using the compact density matrix approach. The confined wave functions and energies of electrons GaN/AlxGA1 – x N are calculated in the effective-mass approximation, solving the Schrödinger equation by Numerov’s method using six order approximations for the derivatives. The calculated results also reveal that by adjusting the widths of well, the barrier and Al concentration respectively, a set of optimal structural parameters can be found for obtaining a strong SHG susceptibility. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2777

Elaboration and characterization of Co-Zn2 SiO4 pigments

In this communication, we reports results on the synthesis of Zn2-xCoxSiO4 (0≤x≤1) ceramic pigments by sol-gel method with the main aim of achieving high purity at lower temperatures. The second objective is to obtain a variety of colours (turquoise, purple, violet and blue) with a minimum quantity as possible as of cobalt. The materials were investigated by X-ray diffraction, infra-red spectroscopy, UV-visible spectroscopy, Lab-colour measurements and Scanning Electron Microscopy (SEM).In this communication, we reports results on the synthesis of Zn2-xCoxSiO4 (0≤x≤1) ceramic pigments by sol-gel method with the main aim of achieving high purity at lower temperatures. The second objective is to obtain a variety of colours (turquoise, purple, violet and blue) with a minimum quantity as possible as of cobalt. The materials were investigated by X-ray diffraction, infra-red spectroscopy, UV-visible spectroscopy, Lab-colour measurements and Scanning Electron Microscopy (SEM)

Structural, Optical and Electrochromic Properties of Sol–Gel V

Vanadium pentoxide thin films are prepared by the sol–gel route by dissolving V2O5 powder (99.5% purity) in H2O2 solution. The solution is spin-coated on glass substrates for optical (UV–VIS–NIR) and XRD analysis, and on ITOcoated glass substrates for electrochromic measurements. The samples are then annealed at 150°C for 1 hour. The resulting films have a yellow-orange color, typical of polycrystalline V2O5. XRD measurements have shown that after annealing in air at 400°C the structure of the films has a c-axis preferred orientation, the (0 0 1)-type planes lying parallel to the substrate. SEM analysis revealed a smooth surface. The films’ optical and physical constants (n, α, Eg, the thickness d and the mean thickness inhomogeneity s) are calculated using a simple and accurate method based on the transmission spectrum alone. The films’ electrochromism is studied using cyclic voltammetry (CV) and chronoamperometry in propylene carbonate solution containing 1 mol/l LiCIO4. The films show reversible multichromism (yellow–green–blue) upon Li+ ion insertion/extraction. The absorbance of films colored at three different potentials is measured in the UV–VIS–PIR wavelength range, and this study shows that the changes in the optical absorption are consistent with the film color changes. Finally, the optical and electrochromic properties of the films prepared by this method are compared with those of our sputtered films already studied and with other works

Dielectric characterization of hydrothermally PREPARED (Cu,Sb)-doped BaTi1-xZrxO3

Powders of copper-doped BaTi1-xZrxO3 have been synthesized using the hydrothermal process. The starting materials were powders of BaO and TiO2, ZrO2.xH2O gel, and an aqueous solution of Cu2+ / Sb5+. The obtained powders were cold compacted and sintered at 1280°C. Impedance spectroscopy measurements have been performed on these ceramics and the results were analyzed using the empiric Cole-Cole model. A procedure to evaluate the electric properties of the grain boundary and bulk grain has been developed based on electric polarization model of double layered dielectrics.Powders of copper-doped BaTi1-xZrxO3 have been synthesized using the hydrothermal process. The starting materials were powders of BaO and TiO2, ZrO2.xH2O gel, and an aqueous solution of Cu2+ / Sb5+. The obtained powders were cold compacted and sintered at 1280°C. Impedance spectroscopy measurements have been performed on these ceramics and the results were analyzed using the empiric Cole-Cole model. A procedure to evaluate the electric properties of the grain boundary and bulk grain has been developed based on electric polarization model of double layered dielectrics

Schottky Diodes and Thin Films Based on Copolymer: Poly(aniline-co-toluidine)

Poly(aniline-co-o-toluidine) (PANI-co-POT) thin films were deposited on indium tin oxide- (ITO-) coated glass substrates by electrochemical polymerization under cyclic voltammetric conditions from aniline-co-o-toluidine monomer in an aqueous solution of HCl as a supporting electrolyte. These measurements showed that the optical band gap of the copolymer films is on the order of 2.65 eV. On the other hand, ITO/PANI-co-POT/Al devices were fabricated by thermal evaporation of Aluminum circular electrodes on the as-deposited PANI-co-POT films. The Current-Voltage characteristics of these devices are nonlinear. The diode parameters were calculated from I-V characteristics using the modified Shockley equation. The C-F characteristics were also measured

Characterization of CuInTe2 thin films prepared by flash evaporation

peer reviewedThin films of CuInTe2 were grown by flash evaporation. The influence of the substrate temperature Ts during film deposition on the properties of the thin films was examined. CuInTe2 films were structurally characterized by the grazing incidence x-ray diffraction (GIXD) technique. Investigation by this technique demonstrates that the surface of thin films of CuInTe2 prepared by flash vaporation at Ts > 100 °C exhibits the chalcopyrite structure with additional binary compounds in the surface. However, in the volume the films exhibit the chalcopyrite structure only; no foreign phases were observed. X-ray reflectometry was utilized to evaluate the critical reflection angle bc of CuInTe2 (bCuInTe2 c 0.32°) which permitted us to calculate the density of the films to be 6 g cm−3. The evaporated films were p type and the films deposited at Ts = 100 °C had a resistivity in the range 0.3–2 cm. From optical measurements we have determined the optical energy gap Eg 0.94 eV and the effective reduced mass m*r 0.07me

Dielectric Behavior of Ceramic (BST)/Epoxy Thick Films

Composite materials were made by mixing powders of Ba1−xSrxTiO3 (x=0.2 and 0.4) ceramics and epoxy resin with various volume fractions (vol%). Dielectric measurements of these composites were performed as a function of filler ratio in the range 100–360°K at 10 KHz. The dielectric constant of the composite increased with increasing volume fraction varies slightly with temperature. The 20 vol% of BST(0.4)-epoxy composite had the highest dielectric constant of 19.4 and dielectric loss tangent of 0.027. Among the dielectric mixing models presented, the model of Lichtenecker shows the best fit to the experimental data for both composites