Browsing by Author "DJELLOUL Abdelkader"

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    CONTROLE DES CENTRES F+ DANS LES COUCHES MINCES D’OXYDE DE ZINC
    (2000) DJELLOUL Abdelkader
    In this study, the interested was focused on the variation of the green luminescence in thin films of ZnO according to the prior processing in an atmosphere of hydrogen. The green luminescence is induced by the singly ionised oxygen vacancy in the form of centre F+. It is established that the concentration of the vacancies could be regularised in the limit of order two for temperatures less than 980 K. For temperatures over 980 K an other defect created in the layers of ZnO which is called interstitial zinc. Keywords: Thin Films, Photoluminescence, Green luminescence, F+ Centre.
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    Peculiarity of the Cathodoluminescence of Αlpha- Alumina Prepared by Calcination of Gibbsite Powder or Generated by Oxidation of a Metallic FeCrAl Alloy
    (2012) DJELLOUL Abdelkader
    Most of metallic materials functioning at high temperature need to have oxidation resistance. This resistance can be achieved when the material develops, through oxidation, an oxide film which acts as a diffusion barrier while keeping a good adherence. In this respect, alpha alumina clearly acts as such. The oxides of aluminum have been the subject of many investigations because of their commercial importance and scientific interest. The thermal stability and optical properties of pure nanometer-sized alumina powder have received much attention because of their intrinsic interest and commercial value. Nanometer-sized alumina powders are widely applied today. One of its applications is in fluorescent lamps due to the absorption of ultraviolet light. In fact, it can also emit the light under excitation with a suitable wavelength. It is important to note that there are many works about alpha alumina using X-ray diffraction, but there is a need for a more detailed structural analysis. To achieve this more exhaustive structural characterization we have used the Rietveld refinement method and cathodoluminescence (CL) measurements.
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    Photoluminescence,FTIRandX-raydiffractionstudiesonundoped and Al-dopedZnOthinfilmsgrownonpolycrystalline a-alumina substrates byultrasonicspraypyrolysis
    (2010) DJELLOUL Abdelkader
    Undoped and aluminum - doped zinc oxide (ZnO )thin films have been grow nonpolycrystalline a-alumin a substrates by ultra sonic spray pyrolysis (USP) technique using zinc acetate dihydrate and aluminum chloride hexahydrate (Alsource) dissolved in methanol, ethanol and deionized water. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) were used to characterize the obtained ZnO obtained ZnO thin films. It was seen that theorientation changed with increasein substrate temperature. During the ZnO deposition Zn source reacted with polycrystalline a-Al2O3 substrate form an intermediate ZnAl2O4 spinellayer. It has been in terestingly found that thein tensityof green emissionat 2.48 eV remarkably increased when the obtained ZnO: Al films were depositedat 380 1C. The FTIR absorbance intensity of spectroscopic bandat 44776 cm 1 is very sensitive to oxygen sublattice disorder resulting fromn on-stoichiometry, which is consistent with the resultof PL characterization
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    PROPRIETES ELECTRIQUES DES COUCHES MINCES D’OXYDE DE ZINC
    (2004) DJELLOUL Abdelkader
    We have investigated the growth conditions on the electric properties of ZnO thin films. Samples were deposited on (1010) , (0001) and (1120) Al2O3 substrates by the chemical vapor transport technique. At room temperature, the carrier concentration and Hall mobility were in the range of 21016 – 8.41018 cm-3 and 140 – 160 cm2V-1s-1, respectively. Results of temperature dependent Hall mobility measurements indicate there are different transport mechanisms at high and low temperatures. Keywords: Thin films. Zinc oxide. Chemical vapor deposition. Hall Mobility
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    Role of Substrate Temperature on the Structural and Morphological Properties of ZnO Thin Films Deposited by Ultrasonic Spray Pyrolysis
    (2008) DJELLOUL Abdelkader
    Zinc oxide (ZnO) thin films have been prepared by ultrasonic Spray Pyrolysis (USP) technique using zinc acetate dihydrate dissolved in methanol, ethanol and deionized water. A thermodynamic analysis for the growth of ZnO thin films from zinc acetate and water vapor has been made. The evolution of the preferred crystalline orientations in the ZnO films was investigated systematically. The optical measurements reveal that films have a maximum transmittance of about 90% and a direct band gap of 3.26 eV. Key Words: Zinc oxide, Ultrasonic spray pyrolysis, Thermodynamic study, X-ray diffraction, Optical properties.
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    Thermochemical and Green Luminescence Analysis of Zinc Oxide Thin Films Grown on Sapphire by Chemical Vapor Deposition
    (2004) DJELLOUL Abdelkader
    This study has been carried out to detail an integral thermochemical analysis of the principal reaction in the production of zinc oxide (ZnO) thin films, including developing an analytical form of the equilibrium constant. Zinc oxide thin films prepared by chemical vapor deposition have been studied in terms of deposition time and substrate temperature. The growth of the single-crystal films present two regimes depending on the substrate temperature, with increasing constant growth rates at lower, and higher, temperature ranges, respectively. Growth rates above 6 um.min−1 can be achieved at Ts = 880 K. The variation of the green luminescence intensities in ZnO single-crystal thin films according to the subsequent processing in hydrogen atmosphere have been studied. After annealing of each ZnO sample at different temperatures, the luminescence intensity is maximal for 𝜆 = 510 nm. It is established that the concentration of the oxygen vacancies could be controlled to within two orders of magnitude for temperatures less than 980 K. Beyond 980 K, defects of interstitial zinc is created in the ZnO films. Key Words: Zinc oxide, chemical vapor deposition, thermochemical, activation energy, hydrogen annealing, green emission.