Papers by Author: Hichem Farh

Abstract: In this recent study, thin films of pure tin oxide (SnO₂) denoted by TO and tin oxide doped with nickel (Ni) and zinc (Zn) at varying concentrations of 5 wt.%, 10 wt.%, and 15 wt.% were developed and characterized on ordinary glass substrates. The deposition of the films was conducted using the sol-gel technique (Dip-coating). These films are referred to as (Ni-Zn) co-doped tin oxide (NZTO) films that can be used in diverse applications such as gas and UV sensors. The effect of Ni/Zn co-doping on the structural, morphological, optical, and electrical properties of undoped SnO₂ was investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. The electrical properties were further examined using the quadruple method. XRD analysis revealed that all samples were polycrystalline with a rutile-type tetragonal crystal structure, predominantly oriented along the (110) plane, but changed to (100) and (200) orientations with high doping contents. The grain size values exhibited a decreasing tendency with increasing co-doping content. The SEM images indicated that the films possessed a porous surface and were made up of well-defined and homogenously dispersed spherical and polyhedron-shaped nanoparticles, which were influenced by doping with Ni and Zn. The FTIR study showed that all the films exhibit the Sn-O-Sn, Sn-O, Sn-OH, and H-O vibration peaks. The NZTO films enhanced the crystal structure and raised the optical energy gap from 4.03 eV for TO to 4.09 eV for NZTO. The thickness also increased from d = 353.44 nm for pure TO films to d = 448.43 nm for films doped with 15% NZTO. The highest transmittance value was observed to be 93% for TO within the visible range. Hall effect measurements indicated that TO exhibited n-type conductivity and p-type conductivity when doped with 5%, 10%, or 15% NZTO. This allows photodetectors based on TO to show great sensitivity to UV light.

Abstract: In this work, we studied the ZnO film thickness effect on the photocatalytic performance of n-ZnO/p-NiO heterostructures. The ZnO and NiO films were prepared by sol-gel dip-coating technique and the thickness of the ZnO film was varied by changing the number of coatingsfrom 2 to12. The formation of the p-NiO/n-ZnO heterostructure was confirmed by X ray diffraction (XRD). The obtained ZnO films present a wurtzite structure with a preferred orientation along (002) direction while the NiO film present a cubic structure highly oriented along (200) direction. UV-visible transmittance spectra of the prepared heterostructures revealed a good transparency in the visible region. The photocatalytic propertiesof the n-ZnO/p-NiO heterostructures were investigated by measuring the degradation rate of methylene blue. All the samples exhibit a good photocatalytic activity under solar light irradiation. The photocatalytic activity of p-NiO/n-ZnO heterostructureswas strongly correlated with the number of ZnO coatings. The highest photocatalytic activity was obtained at 6 coatings with a degradation rate of methylene blue equal to 98.67% for 4.5h of irradiation.

Abstract: We propose here a method witch analyze the behavior of Quasi-square open ring frequency selective surface (FSS) by using an approach based on the wave iterative concept procedure method (WCIP) coupled to Retrieval from Scattering Parameters method . The scattering parameters calculated by WCIP for a Quasi-square open ring FSS are used, in analytical formulas, to calculate directly observable effective constitutive parameters (relative electric permittivity ε_reff , magnetic permeability μ_reff and refractive index n ) of a frequency selective surface. Results of effective constitutive parameters for a Quasi-square open ring FSS structure are presented by Simulation using MATLAB program codes translating the implementation of the proposed approach.

Abstract: Zinc oxide Nanorods (ZnO-NRs) were deposited onto glass substrates using zinc chloride by Ultrasonic Spray Pyrolysis (USP) method. The films were prepared in different deposition time at optimum deposition parameters. The effect of deposition time on the structural, morphological and optical properties of ZnO-NRs was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectrometry (UV-Vis). XRD and SEM measurements indicated that all films show a hexagonal wurtzite Nano rods (NRs) structure growing preferentially along c-axis perpendicular to the surface of the substrate. Optical transmission spectra showed high transmittance of 80-85% in the visible range for all thin films, and increase of optical band gap from 3.24 to 3.265 eV with deposition time. The high quality c-axis orientated ZnO thin films with minimum strain and tuneable optical properties could be used as a transparent conducting oxide (TCO) for optoelectronic applications.

Abstract: In this work, we studied the effect of pre-heating temperature on the structural and optical properties of ZnO nanorods grown by free template sol-gel dip-coating technique. The prepared films were pre-heated at different temperatures: 240, 260, 280 and 300 °C, then annealed at 500 °C for one hour. The structural properties of the prepared samples were investigated by X-ray diffraction (XRD) and the surface morphologies were studied by scanning electron microscope (SEM). The optical properties were studied by means of UV-Visible spectrophotometer. The XRD diffraction spectra show that all the prepared samples have a ZnO wurtzite structure with a preferential orientation along (002) axis. SEM micrographs revealed the formation of well-aligned ZnO nanorods for the sample preheated at 280 °C. The prepared ZnO nanorod structured thin films are highly transparent in the visible region with an average transmittance above 85 % in the 400–800 nm wavelength range.

Abstract: The precipitation of two 6xxx (Al-Mg-Si) alloys with and without copper (Cu) and excess silicon (Si) has been investigated by using the differential scanning calorimetry (DSC), transmission electron microscopic (TEM) and X ray diffraction (XRD) analysis. The analysis of the DSC curves found that the excess Si accelerate the precipitation. The values of activation energies for each peak of DSC curves were determined by using Kissinger–Akahira–Sunose (KAS) and Boswell isoconversional methods. The alloy which has an excess Si and copper require larger activation energy for precipitation despite the acceleration of the precipitation by the excess Si. TEM observation result shows there is smaller size and higher density of precipitate in excess Si alloy than those of excess-free.

Abstract: The rolling operation consists of deforming the material by passing it between two rolls whose spacing is smaller than the initial thickness of the sample, the reduction in thickness is obtained discontinuously by successive passes in the rolling mill whose spacing between the cylinders gradually decreases. This operation can influence on the mechanical and microstructural properties of the deformed materials The effect of cold rolled on microstructural evolution and precipitation sequence in Al-Mg-Si alloy has been investigated by using optical microscopy and Differential Scanning Calorimetry (DSC) in this study. The results revealed that the distribution of the grains are elongated along the rolling direction. We also noted that insoluble coarse particles that originated during the manufacturing process of the alloy have become visible after the rolling processes. The dislocations generated by the plastic deformation during cooled rolling constitute preferential sites for the germination and the growth of the phases, which accelerates the kinetics of the precipitation.

Abstract: In this manuscript, the structural properties such as the distance inter-reticular of samples is studied, In the fact, four samples were used symbolized as follows: E tAg(Å), the only difference is the thickness of the Silver buffer layer (tAg= 0, 50, 100 and 150 Å) to find out how the thickness of this layer depends on the structural characteristics of the Iron thin layer, all samples are deposited using molecular beam epitaxy (MBE) at room temperature onto Si (100) substrate. The structural properties of all samples examined using X-ray diffraction method at small and high angles. The small angles X-Ray diffraction curves confirmed to us that there is a clear difference between the surface structure of the samples by varying the number of Kiessig Fringes, Also high angles X-Ray diffraction curves assured us this difference through the clear variation in the angular positions of the peaks of Bragg and the distances inter-reticular values from a sample to the other.

Abstract: In this paper, the influence of immersion time on the structural and optical properties of SnO2 thin films was investigated. A series of samples was deposited by Sol-Gel dip coating method onto glass substrates. The number of layers was fixed at 03, but the immersion time was varied between 01 to 10 minutes. The samples [(3 layers) - SnO2 / glass] were submitted to thermal treatments in air at 500°C during 2h. The specimens are characterized by Raman spectroscopy and UV-Visible spectroscopy. Raman spectroscopy show that the thin films of SnO2 obtained at 06 and 10 minutes of immersion time, are crystallizes in rutile phase. The obtained results of optical analysis showed that the SnO2 thin films are transparent (77-85%) in the visible region and the values of the optical band gap varied from 3.81eV and 3.86 eV.

Abstract: The use of phase change materials must allow storage / destocking of energy from solar or internal gains. The applications in the case of light constructions will lead to an improvement in the thermal comfort of users and a reduction in energy consumption. The use of phase change materials (PCMs) in the energy-saving walls themselves makes it possible to substitute sensible heat storage for latent heat storage which requires a much lower volume and mass for the same amount of thermal energy. The objective of this work is the study of heat transfer by conduction during a phase change, and aims on the one hand to model and simulate the phase change behavior and on the other hand to approach the mechanism of heat exchange at the solid-liquid interface. The results obtained in 2D show the temporal evolution of the temperature, the position and the speed of the solid-liquid interface.