الفهرس 
ACKNOWLEDGEMENTOnly 14 pages are availabe for public view
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Abstract
This thesis is systematic investigation of the structural and optical properties of ternary alloys containing silver (Ag). Alloys of all compositions were prepared by melt-quench technique and thin films deposited on glass substrates using the thermal evaporation technique at room temperature.
X-Ray diffraction (XRD) patterns of the as-prepared As30Te70-xAgx (x = 5 and 10 at. %) thin films show the absence of sharp peaks which mean that the samples were amorphous. The transmission (T) and reflection spectra (R) of as-prepared As30Te70-xAgx (x = 5 & 10 at. %) thin films are measured at normal incidence in the spectral range 200-2500 nm. Analysis of the optical absorption data showed that indirect transition are participating. Increasing silver content has resulted in decreasing of the optical band gap (Eg) and increasing of the band tail width (Ee). The obtained values of the optical band gap were discussed in terms of electronegativity (χ), cohesive energy (CE) and ionization energy changes with Ag content. The optical constants such as refractive index n and extinction coefficient k of the films were determined. The refractive index dispersion curves of the films were found to obey the single oscillator model and the oscillator parameters changed with Ag content.
The structure of the as-prepared and thermal annealed of As30S60Ag10 chalcogenide glass is characterized using the XRD and Scanning Electron Microscopy (SEM). Differential Scanning Calorimetry (DSC) curves recorded at four different heating rates were analyzed to determine the glass and crystallization transition temperatures, thermal stability and enthalpy release. Two separated crystallization peaks were observed in the DSC curves. XRD results indicated the precipitation of AgAsS4 crystal phase was responsible for the first peak. Numerous phases with S8 dominant phase were accountable for the second peak. The crystallization kinetics such as the activation energy for the crystallization (Ec), the frequency factor (Ko) and the crystallization rate constant K were determined for each crystallization stage. The results showed that the crystallization rate constant for the first crystallization stage is about six times larger than that of the second crystallization step.
Chalcogenide As30S60Ag10 thin films were prepared using the thermal evaporation technique from the bulk alloy. The effect of thermal annealing on the structural, optical properties of As30S60Ag10 thin films was studied. XRD patterns showed that the as-prepared and annealed films at 453, 500 and 573 K for 1 hour are polycrystalline. These results were confirmed by SEM investigations. The crystallite sizes were calculated for annealed films. Transmission spectra showed that the as-prepared and annealed films have highly transparent over the visible region. The presence of a sharp absorption edge for all films in the transmission spectra recommends As30S60Ag10 thin films as a good optical filter material. The improvement in transparency upon annealing is due to the enhancement in the crystallinity. The decrease in both optical band gap and refractive index of annealed films after crystallization temperatures was discussed in accordance with the structure changes upon annealing.
Optical properties for thin films of As30S60Ag10 of thicknesses 75, 150, 225 and 450 nm were studied . The transmittance and reflectance of the films were measured in the wavelength range 200-2500 nm. The optical band gap decreased while the width of the localized states tail increased with increasing the film thickness. Variation of refractive index and extinction coefficient with the film thickness were studied. The dispersion of the refractive index was described using the Wimple–DiDomenico (WDD) single oscillator model and the dispersion parameters were calculated as a function of film thickness. Also, the high frequency dielectric constant (ε∞) and the ratios of the free carrier concentration to its effective mass (N/m*) were studied.
Chalcogenide thin films of Ge20Se70Ag10 of thicknesses 150, 300 and 450 nm were prepared by thermal evaporation technique. The crystalline phases of the deposited film were identified by X-ray diffraction. The transmittance and reflectance of the films were measured in the wavelength range 200-2500 nm. The optical band gap was found to be decrease while the width of the localized states tail increased with increasing the film thickness.
Variation of refractive index and extinction coefficient with the film thickness were studied to analyze the optical efficiency of these films. Application of the single oscillator model to the films revealed that the oscillator energy decreased while the dispersion energy increased with increasing thickness. The variation of the optical constants suggests that the thickness change is a good choice to control the optical properties of Ge20Se70Ag10 film.