الفهرس 
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Abstract
Summary and conclusions
The structural and optical properties of AsxSe100-x compositions ranging from (x =5-50 at. %) alloys were studied. Bulk materials were prepared using the well known melt-quench technique. The investigated compositions in the thin film form were deposited on glass substrates using the thermal evaporation technique at room temperature. The main conclusions that can be drawn from this thesis can be summarized as follows:
• Structural properties of AsxSe100-x thin films
The XRD analysis of AsxSe100- x (5 ≤ x ≤ 50) compositions emphases the amorphous structure of the prepared samples either in bulk or in thin film form. We calculated some theoretical parameters that are related to the arsenic content change in the AsxSe100-x system. In the present compound of AsxSe100-x, the rigidity percolation threshold (RPT) occurs at As=40 at.%.
• Thermal analysis of AsxSe100-x chalcogenide glassy alloys
Effect of As atoms as modifiers (cross-linking of polymeric Se structure) and the formation of the glass network was investigated by detailed analysis of the compositional trend of Tg of AsxSe100-x network glasses. The existence of a linear region in the Tg(x) relationship at small values of x can be accounted for on the basis of the stochastic agglomeration theory and similar theoretical models which predict a slope equations. Some of the disagreements between the predictions of the theoretical models and the experimental data can be attributed to the complexity of the molecular structure in the AsxSe100-x network glasses, in particular, at higher values of x. Proper understanding of the dominant local structure of the glass network at different composition is essential for any attempt to describe in details the nature of the covalent glass network.
• Studies on the structural and optical properties of AsxSe100-x thin films
The optical characterization of the different compositions of amorphous AsxSe100-x semiconducting films (x =5-50 at.%) has been carried out using the transmittance and reflectance spectra. The envelope method suggested by Swanepoel has been applied to the films. The optical characterization shows that the refractive index of the AsxSe100-x thin films increases and the fundamental band gap decreases from 1.91 to 1.77 eV with increasing arsenic content upto 40 at.% and increase for films containing As >40 at.%. The behavior of the refractive index dispersion and its dependence on composition of amorphous AsxSe100-x thin films were discussed using single oscillator model.
• Effect of thickness on the optical properties of As40Se60 thin films
It is found that Eg is decreasing with increasing thickness due to increasing the band tailing. The behavior of absorption coefficient, refractive index and extinction coefficient of the films is found to be depended on the film thickness. Moreover, the dispersion parameters Ed, Eo, e∞ and the ratio N/m* were found to be sensitive to the change in the film thickness.