K.A. Aly

Characterization of new quaternary chalcogenide As-Ge-Se-Sb thin films

This paper reports the effect of replacement of selenium by antimony on the optical gap and some other physical parameters of new quaternary chalcogenide As14Ge14Se72− x Sb x (where x = 3, 6, 9, 12 and 15 at%) thin films. Thin films with thickness 200–220 nm of As14Ge14Se72− x Sb x were prepared by thermal evaporation of the bulk samples. Increasing antimony content was found to affect the average heat of atomization, the average coordination number, number of constraints and cohesive energy of the As14Ge14Se72 −x Sb x alloys. Optical absorption measurements showed that the fundamental absorption edge is a function of composition. Optical absorption is due to allowed, non-direct transition and the energy gap decreases with the increasing antimony content. The chemical bond approach has been applied successfully to interpret the decrease in the optical gap with increasing antimony content.

Compositional dependence of the optical properties of amorphous Se100-xTex thin films

Thin films of amorphous Se100 –x Te x with different compositions (x = 10, 20, 30 and 40 at%) were deposited on glass substrates by thermal evaporation. Transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 17 896 (1984)], using of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction plus film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model [Phys. Rev. B 3 1338 (1971)]. The optical band gap was determined from the spectral dependence of the absorption coefficient using the Tauc formula [in The Optical Properties of Solids, edited by F. Abeles (North Holland, Amsterdam, 1970), p. 227]. The refractive index increases and the optical band gap decreases with increasing tellurium content.

Effect of WO3 on the glass transition and crystallization kinetics of borotellurite glasses

Tellurite glasses of the system xWO3–75TeO2–(25 − x)B2O3 (0 ≤ x ≤ 25 mol. %) were prepared and studied by differential thermal analysis to explore the effect of WO3 on their glass transition and crystallization kinetics. The crystallization kinetics was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed and both the activation energy of the crystallization process and the crystallization mechanism characterized. The phases into which the glass crystallizes were identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-tellurite, Te0.95W0.05O2.05, Te2W and B2O3 in the amorphous matrix.

Determination of the thickness and optical constants of amorphous Ge–Se–Bi thin films

The effect of varying bismuth concentration on the optical constants of amorphous Ge20Se80− x Bi x (where x = 0, 3, 6, 9 and 12 at%) thin films prepared by thermal evaporation has been investigated. The transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. An analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 16 (1983) p.1214], based on the use of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing bismuth content was found to affect the refractive index and extinction coefficient of the Ge20Se80− x Bi x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing bismuth content, the refractive index increases while the optical band gap decreases.

Optical constants of quaternary Ge-As-Te-In amorphous thin films evaluated from their reflectance spectra

Thin films of amorphous Ge9As20Te71− x In x with different compositions (x = 0, 3, 6 and 9 at. %) were obtained by deposition onto glass substrates by thermal evaporation. The reflection spectra, R(λ), of the films were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Ruiz-Perez et al., based on the use of the maxima and minima of the interference fringes, has been applied to derive the real and imaginary parts of the complex index of refraction, the thickness and the thickness variation of the studied films. Increasing In content is found to affect the refractive index and the extinction coefficient of the films. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing In content, the refractive index decreases, whereas the optical band gap, Eg , increases. The relationship between Eg and the chemical composition of the Ge9As20Te71− x In x system is discussed in terms of the cohesive energy, the average heat of atomization, H s , and the average coordination number, N r .

Thermal stability and activation energy of some compositions of Ge-Te-Cu chalcogenide system

The present study investigates the influence of copper addition on the thermal stability, and the activation energy of the glass transition and crystallization for Ge26Te74− x Cu x (x = 2.5, 5, 7.5, 10 and 12.5 at%) glasses. Differential scanning calorimetric (DSC) results under non-isothermal conditions for the Ge–Te–Cu system are reported and discussed. From the heating rate (α) dependence of the glass transition temperature (T g) and the temperature corresponding to the maximum crystallization rate (T p), the activation energy for both glass transition and crystallization for the studied glasses were obtained. The glass-forming ability of the Ge26Te74− x Cu x glasses was evaluated using various thermal stability criteria based on characteristic temperatures. The K r(T) criterion has also been considered for the evaluation of glass stability from DSC data. The activation energy for crystallization decreases and thermal stability increases with increasing copper content.

Thermal stability and crystallization kinetics of Ge–Se–Cd glasses

The effect is reported of varying cadmium concentration on the glass transition, thermal stability and crystallization kinetics of Ge20Se80− x Cd x (x = 2.5, 5, 7.5 and 10 at. %) glasses. Differential scanning calorimetry results under non-isothermal conditions for the studied glasses are reported and discussed. The values of the glass transition temperature (Tg ) and the peak temperature of crystallization (Tp ) were found to be dependent on heating rate and Cd content. From the heating rate dependence of Tg and Tp , the values of the activation energy for glass transition (Eg ) and the activation energy for crystallization (Ec ) were evaluated and their composition dependence discussed. The thermal stability of the glasses was evaluated using various thermal stability criteria such as ΔT, Hg and S. The stability calculations emphasize that the thermal stability decreases with increasing Cd content.

Some Physical Features of Glasses Synthesized from Some Environmental Wastes

New glasses based on wastes of limestone, phosphate, and cement kiln dust besides white sand were manufactured. The structure of the prepared glasses was studied by FTIR, thermal analysis, UV spectroscopy and ultrasonic techniques. The analysis revealed that increasing the content of SiO2 influences the concentrations of the structural units constituting the amorphous network. The values of the physical parameters; the density, ultrasonic velocity, the elastic moduli, the refractive index, the optical band gap and the glass transition temperature increase as the SiO2 content increases, which was attributed to the former role of SiO2 which strengthens the calcium borate network and the conversion of non-bridging oxygens into bridging oxygens. These factors increase the crosslink density and connectivity within the glass network and hence its rigidity.

Crystallization study of Se 86 Sb 14 glass

The present study concerns with high-accuracy determination of crystallization activation energy (