Abstract: The present work deals with the preparation and characterization of cadmium sulfur (CdS) thin films. These films are prepared by chemical bath deposition on the well cleaned glass substrates. The thickness of the samples was measured by using profilometer DEKTAK, structural and optical properties were studied by X-ray diffraction analysis, and UV-visible spectrophotometry. The optical properties of the films have been investigated as a function of temperature. The band gap energy and Urbach energy were also investigated as a function of temperature. From the transmittance data analysis the direct band gap ranges from 2.21 eV to 2.34 eV. A dependence of band gap on temperature has been observed and the possible raisons are discussed. Transmission spectra indicates a high transmission coefficient (75 %). Structural analysis revealed that the films showed cubic structure, and the crystallite size decreased at a higher deposition temperature.
Abstract: In this work, we report the study of functionalized platinum (Pt) electrodes based on a polymeric membrane (PVC) including an ionophore (ethyln diamin tetracetic EDTA) sensitive for mercury ions Hg2+. The optimised working conditions of the sensors have been studied with regard to the sensitivity performances; in particular, the polarisation was adjusted to - 0.2V/SCE. Ion sensitivity of sensors have been tested for Hg(II) via Cd(II) in aqueous solution. A layer of EDTA deposited on platinum electrode has been characterised by impedance spectroscopy and cyclic voltammetry methods.
Abstract: Hydrogel based on acrylamide and acrylic acid was synthesized and crosslinked by gamma radiation at an absorbed dose of 8 kGy. Swelling properties of the hydrogel in water and in methyl violet and Congo red solutions were investigated. The results showed that the swelling rate of the hydrogel depends on the pH and the ionic nature of the dye. Diffusion of water and dyes solutions within the hydrogel was found to be of non-Fickian character. Contrary to the swelling behavior, the capacity of the hydrogel to adsorb dyes seems to be higher at weak pHs. Concerning metal ions uptake, the results showed that adsorption of Cu2+ increases with pH increasing from pH1 to pH4.
Abstract: The hydrogen-sensing property of new type field-effect gas sensor device was studied. The device had an FET structure based on porous silicon. Adsorption of molecules into the porous silicon strongly changes the electrical properties of the transistor structure. Interestingly, the current variation induced by Hydrogen gas vapour that is the sensitivity of the sensor can be electrically tuned by changing polarization voltage. It has been shown that the device exhibited excellent hydrogen-sensing characteristic at room temperature. The results show that current-voltage characteristics are modified by the gas reactivity on the PS surface.
In conclusion, the FET gas sensor based on porous silicon shows a rapid response to low concentration of the hydrogen gas at room temperature.
Abstract: In this work we report the optical characteristics of carbon nitride films produced by a KrF excimer laser ablation technique. The ablated materials were collected on different wafers, glass and porous silicon for different N2 pressures (0.1-0.5mbar). The thin films were synthesized at room temperature. The deposited thin films were characterized by spectrophotometry, ellipsometry, scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results show that the optical band gap deduced from optical transmission spectra in the ultraviolet- visible – near infrared range increases with deposition time and with nitrogen pressures increasing. SEM observation indicates that the CNx film is granular. Finally, FTIR spectra reveal carbon nitride absorption bands which do not seem change considerably with N2 pressures.
Abstract: We investigate the application of porous silicon (PS) in the field of the photovoltaic. In first step we realise a double porous silicon layer by electrochemical anodisation using two different current densities. The low current leads to a low porosity and during annealing, the recrystallisation of this layer allows epitaxial growth. The second current leads to a high porosity which permits the transfer onto a low cost substrate. During high temperature onto hydrogenation treatments of to passivate the structure and epitaxy in liquid phase, porous silicon is recristallized partially. In this work, a characterization by scanning electron microscopy informs us about the morphology of these porous layers.
Abstract: The microroughness of the semiconductor/oxide interface substantially influence properties of the whole structure. In our work Si/SiO2/SiOx structures were prepared by using low temperature nitric acid oxidation technique and by the electron gun technique and then the whole structure was passivated by the HCN technique. In the present study we investigate the surface morphology evolution during the creation of the SiO2/SiOx double-layer and after the passivation steps. Surface roughness properties are studied by the fractal geometry methods. The complexity of analysed surface is sensitive to the oxidation and passivation steps and the proposed fractal complexity measure values enable quantifying of the fine surface changes.
Abstract: . Experimental results relating to evolution of the a-Si:H photoluminescence spectra are presented. The investigated samples were prepared by deposition of thin a-Si:H layer on glass substrate. In the a-Si:H surface region very thin oxide layer was prepared by wet chemical oxidation in 40% nitric acid solution. The defect states of amorphous silicon layer and its interface with oxide were passivated in HCN aqueous solutions. The attention was focused on decomposition procedure of photoluminescence spectra observed at 6 K. The results confirm the existence of several structurally different phases inside of the a-Si:H amorphous matrix.
PACS: 78.55.-m, 78.55.Qr, 81.05.Gc
Abstract: The cellulose made up the principal structure of many plants. The content varies according to the vegetable species, from approximately 40% in wood, to 95-99% in cotton fibers. Several ways are possible to bring an additional function to cellulose: new fibers, modification of the fibrous structure, physical or chemical treatment by a surface treatment. And due to the contribution of functions, the formerly passive cellulose becomes active. Capacity of cyclodextrins to facilitate the inclusion of hydrophobic molecules, and others chemical derivatives like the dyes, can be exploited to obtain new porous materials modify with particular performances. In this work, a porous cellulosic material modifies was obtained by chemical modification and fixing of β-cyclodextrin on polymeric surface. The results were confirmed by infra-red analysis (FTIR) and scanning electron microscopy (SEM). The experiments of adsorption of balance of a reactive dye were made in aqueous solutions for 48 hours. Our results indicate the formation of a permanent chemical bond between the β - cyclodextrin and the fibrous material, and the modification is done without change of the polymer structure, the inclusion of the molecules of dyes in the cavity of cyclodextrin is due to the several interactions. The results of dye adsorption in aqueous medium show the aptitude of porous materials to fix the dangerous industrial dyes, and used in the processing industrial liquid waste.