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Laatar F.,Center for Research and Technology Energy | Harizi A.,Tunis el Manar University | Smida A.,Center for Research and Technology Energy | Hassen M.,Center for Research and Technology Energy | And 2 more authors.
Materials Research Bulletin | Year: 2016

Cadmium selenide quantum dots (CdSe QDs) thin films were deposited onto glass substrates by a chemical bath deposition (CBD) method at different temperatures from an aqueous solution containing l-Cysteine (l-Cys) as capping agent. The evolution of the surface morphology and elemental composition of the CdSe films were studied by AFM, SEM, and EDX analyses. Structural and optical properties of CdSe thin films were investigated by XRD, UV-vis and PL spectroscopy. The dispersion behavior of the refractive index is described using the single oscillator Wemple-DiDomenico (W-D) model, and the physical dispersion parameters are calculated as a function of deposition temperature. The dispersive optical parameters such as average oscillator energy (Eo), dispersion energy (Ed), and static refractive index (no) were found to vary with the deposition temperature. Besides, the electrical free carrier susceptibility (χe) and the carrier concentration of the effective mass ratio (N/m∗) were evaluated according to the Spitzer-Fan model. © 2016 Elsevier Ltd. All rights reserved. Source


Laatar F.,Center for Research and Technology Energy | Laatar F.,University of Carthage | Hassen M.,Center for Research and Technology Energy | Hassen M.,Higher Institute of Applied Science and Technology of Sousse | And 4 more authors.
Journal of Luminescence | Year: 2016

In this paper, Porous anodic alumina (PAA) template with highly ordered nanopores structure was synthesized on aluminum foils by two step anodization process. PAA template has hexagonal pores with average size between 30 and 180 nm. L-cysteine (L-Cys) functionalized cadmium selenide nanocrystals (CdSe NCs) were successfully embedded inside PAA layers by simple immersion in aqueous solution. The effect of pore diameter enlargement on the microstructure of CdSe NCs/PAA films was systematically studied by FE-SEM, XRD, EDX, Raman, UV-VIS absorbance and PL analysis. FE-SEM microscopy was used to investigate the surface morphology of PAA templates before and after CdSe NCs deposition. XRD investigation demonstrates that CdSe NCs into PAA templates were cubic in nature with zinc-blende structure. Raman measurements exhibit the characteristic modes of CdSe on the PAA layers as well as the films crystallinity as function of widening pores diameter. Optical properties of deposited CdSe NCs on PAA templates have been investigated using optical absorption and PL techniques. Photoluminescence spectroscopy has been used to determine the bandgap energy and the average size of CdSe NCs deposited on PAA layer. This method involves fitting the experimental spectra, using a model based on quantum confinement of electrons in CdSe nanocrystals having spherical and cylindrical forms (Quantum Dots (QDs) and Quantum Wires (QWs)). This model allows correlation between the PL spectra and the microstructure of the CdSe/PAA. Both photoluminescence and optical absorption show that the PL peak energy and the optical absorption edge of CdSe NCs/PAA exhibit similar behavior with changes in nanostructure size. The spectral behaviors of optical absorption and PL are consistent with a quantum confinement model throughout the sizes and shapes of the CdSe nanocrystals of the luminescent films. The effective bandgap energies determined from the PL peaks position are in good agreement with those estimated from the optical absorbance spectra. Investigations have shown that optical properties of CdSe/PAA nanostructure were influenced by the pores sizes of PAA. It was observed an increase in CdSe NCs size from 2.22 to 2.56 nm when the average pores diameter of PAA increases from 30 to 180 nm. This finding indicates an enhancement in PL intensity and a red-shift in PL emission peaks from 2.35 to 2.14 eV. By applying the quantum confinement model, we demonstrated that the redshift of PL peak is attributed to the change of CdSe NCs size with the pores diameter and that their spectral behaviors are related to the shape and the size distribution of the nanoparticles. © 2016 Elsevier B.V. All rights reserved. Source


Smida A.,Center for Research and Technology Energy | Laatar F.,Center for Research and Technology Energy | Hassen M.,Center for Research and Technology Energy | Hassen M.,Higher Institute of Applied Science and Technology of Sousse | Ezzaouia H.,Center for Research and Technology Energy
Journal of Luminescence | Year: 2016

This paper consists to present first results concerning the structure of porous GaAs layer (por-GaAs-L) prepared by using HF/HNO3 as acidic solution in vapor etching (VE) method. In order to clarify this method, we detail here its principle and explain how por-GaAs-Ls are formed, taking into account the influencing of the exposure time of the GaAs substrate to the acid vapor. The etched GaAs layers have been investigated by UV-visible and PL analysis. One porous layer was performed to be characterised by Atomic Force Microscopy (AFM), FTIR spectroscopy, and X-Ray Diffraction (XRD). The porous structure was constituted by a nanocrystals with an average size about 6 nm. These nanocrystals were calculated from XRD peak using Scherrer's formula, AFM imaging, and also by using effective mass approximation model from effective band gap. © 2016 Elsevier B.V. All rights reserved. Source


Laatar F.,Center for Research and Technology Energy | Hassen M.,Center for Research and Technology Energy | Hassen M.,Higher Institute of Applied Science and Technology of Sousse | Smida A.,Center for Research and Technology Energy | And 3 more authors.
Superlattices and Microstructures | Year: 2015

In this work, cadmium selenide nanocrystals (CdSe NCs) were embedded into porous anodic alumina (PAA) template by simple immersion in aqueous solution containing l-cysteine (Cys) functionalized CdSe NCs and water. The prepared samples were heat treated at different temperatures between 150 and 300 °C during 30 min under air. The effect of thermal treatment under air on the CdSe NCs/PAA has been shown from morphological, microstructural and optical studies. Several characterization techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) spectroscopy were used to investigate the surface morphology and microstructural properties of CdSe nanoparticles on the PAA template as function of air-annealing temperature. XRD study shows the transformation phase of deposited CdSe nanoparticles on the PAA template from cubic structure to hexagonal structure at 300 °C. The morphology of CdSe nanorods array which are into the PAA surface were exhibited by AFM scan. Optical properties of CdSe NCs into PAA have been studied at different air-annealing temperatures using optical absorption and photoluminescence (PL) spectroscopy. The results showed that the crystal quality was significantly improved with the annealing temperature increase, bringing about an enhancement in PL and a decrease in optical band gap from 2.44 to 2.2 eV exhibiting a red shift. © 2015 Elsevier Ltd. All rights reserved. Source

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