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F. Ben Nasr A. Matoussi S. Guermazi Z. Fakhfakh 《Materials science & engineering. C, Materials for biological applications》2008,28(5-6):618-622
In this work, we consider a 2D model for calculation of cathodoluminescence in GaN-based structures. This model is developed using an extended generation profile and taking into account the influence of the carrier diffusion process, internal absorption and some radiative recombination processes. First, we have investigated the effect of hole diffusion length and the surface recombination velocity on the CL spectra of GaN sample grown at 800 °C by MOVPE method. Then, we have calculated the dependence of CL intensity from AlGaN alloys as a function of Al content and the electron beam energy.
Results show a red shift of the CL peaks when the beam energy is varied from 2 to 10 keV at room temperature. The band-edge emission of AlxGa1 − xN shifts about 0.49 eV when the Al composition is increased from x = 0.18 to 0.38. Comparison of the experimental spectra with simulations shows a good agreement. 相似文献
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Mohamed Guermazi H. Jurgen Höfler Horst Hahn Robert S. Averback 《Journal of the American Ceramic Society》1991,74(10):2672-2674
Vickers hardness of nanocrystalline ( N -) TiO2 was measured in the temperature range 25° to 1200°C and it was compared with that of polycrystalline ( P -) TiO2 in the same temperature range. N -TiO2 showed a lower hardness than P -TiO2 at temperatures up to 800°C which resulted in the lack of indentation crack traces for N -TiO2 presumably implying more plasticity. 相似文献
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Majdi Kahouli Nabil Tounsi Nissaf Mzabi Hajer Guermazi Samir Guermazi 《Advanced Powder Technology》2018,29(2):325-332
ZnO nanopowders of tailored particle sizes were synthesized using a simple wet chemical method, by controlling the mass ratio of the precursors. The physical properties were investigated as a function of OH?/Zn2+ mass ratio (x). The structural properties of the synthesized nanoparticles (NPs) are studied using X-ray diffraction (XRD). XRD patterns show pure wurtzite structure. Microstructural parameters dependence on x ratio was studied based on Williamson-Hall model. We notice an increase in crystallite size (17–24?nm) and a decrease in strain values when the x ratio increases (0.5–1.4). The best crystallinity corresponds to the higher mass ratio. Indeed, for x?=?1.4 we obtain the largest crystallite size, the lowest strain and stacking faults. The TEM images support the XRD results. Raman spectra confirm the purity of the synthesized ZnO powder. Furthermore, the optical properties were examined by UV–vis and Photoluminescence as a function of precursor’s ratio. Absorption data show a band gap red-shift of the ZnO-NPs with increase in particle’s size. Moreover, we found that the ZnO-NPs luminescence in the visible range can be engineered by changes of x ratio. This constitutes an advantage for the use of ZnO-NPs in different wavelength areas in optoelectronic applications covering UV-Blue-Green domain for the LED design, sensors… 相似文献
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Rajeh S. Souissi R. Ihzaz N. Mhamdi A. Bouguila N. Labidi A. Amlouk M. Guermazi S. 《Journal of Materials Science: Materials in Electronics》2022,33(22):17513-17521
Journal of Materials Science: Materials in Electronics - Undoped and Ni-doped ZnO thin films were grown on glass substrates at 460 °C using the spray pyrolysis method. All samples... 相似文献
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Abir Abdelkefi Pierrick Malécot Nathalie Boudeau Noamen Guermazi Nader Haddar 《The International Journal of Advanced Manufacturing Technology》2017,93(5-8):1725-1735
It is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test. 相似文献
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A. Matoussi T. Boufaden A. Missaoui S. Guermazi B. Bessaïs Y. Mlik B. El Jani 《Microelectronics Journal》2001,32(12):995-998
We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (Tg) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When Tg increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures. 相似文献
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A. Matoussi T. Boufaden S. Guermazi Y. Mlik B. El Jani A. Toureille 《Journal of Electronic Materials》2005,34(7):1059-1064
In this article, we report the electron beam-induced current (EBIC) measurements in a GaN Schottky diode performed in the
line-scan configuration. A theoretical model with an extended generation source was used to accurately extract some minority
carrier transport properties of the unintentionally doped n-GaN layer. The minority hole diffusion length is found to increase
from ∼0.35 μm near the junction to ∼1.74 μm at the bulk regions. This change is attributed to an increase of the carrier lifetime
caused by the polarization effects, which are preponderant in this component. For depth distances exceeding 0.65 μm, it is
shown that the measured current is produced by the reabsorption recombination radiation process. This corresponds to an absorption
coefficient of 0.178 μm−1, in good agreement with the optical absorption measurement. 相似文献
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Hichem Smaoui Nissaf Mzabi Hajer Guermazi Youssef Mlik Serge Agnel Alain Toureille François Schué 《Polymer International》2007,56(3):325-332
The performance of insulators is usually affected by the presence of space charges. The evolution of these charges under applied constraints in many cases leads to the degradation of these materials. To evaluate the performance of an insulator it is necessary to study the evolution of the physical and chemical properties in the presence of space charges. In this paper, the effect of gamma irradiation on the space charge behaviour in polyetherimide (PEI; Ultem 1000) has been investigated at different radiation doses. Space charge measurements were made using thermally stimulated currents. Infrared spectroscopy characterisation was performed to investigate the effect of gamma irradiation on the physicochemical properties of PEI. The results obtained show minor differences in the infrared spectra, mainly in the 410 cm?1 region. It is found that irradiation leads to a few structural changes in the material. The thermostimulated depolarisation current (TSDC) results show that β relaxations in PEI are affected by gamma irradiation. The activation energies of dipoles were calculated from the TSDC curves. Copyright © 2006 Society of Chemical Industry 相似文献