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Structural and optical characterization of annealed As30Te60Ga10 thin films prepared by thermal evaporation technique

Abd-Elnaiem A. M., Mohamed M., Hassan R. M., Abdel-Rahim M. A., Abu-Sehly A. A., Hafiz M. M.

Materials Science Poland

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2018

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Vol. 36, No. 2

193--202

EN

Effect of annealing temperature on the structural and optical properties of As30Te60Ga10 thin film was studied using various techniques such as differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The DSC analysis revealed that the As30Te60Ga10 glass has a single glass transition and crystallization peak while XRD results confirmed that the as-prepared and annealed films have crystalline nature. The coexistence of the crystalline phases in the investigated films could be attributed to the formation of orthorhombic As, hexagonal Ga7Te10, and monoclinic As2Te3 phases. It was found that the average crystallite size and optical parameters of the studied films depend on the annealing temperature. For example, the optical band gap decreased from 1.54 eV to 1.11 eV as the annealing temperature increased from 300 K to 433 K.

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Influence of annealing temperature on the structural and optical properties of As30Te70 thin films

Abd-Elnaiem A. M., Mohamed M., Hassan R. M., Abu-Sehly A. A., Abdel-Rahim M. A, Hafiz M. M.

Materials Science Poland

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2017

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Vol. 35, No. 2

335--345

EN

Chalcogenide glasses have attracted much attention largely due to their interesting physical and chemical properties. Though few published articles exist on the As-Te system, little is known about the optical properties of eutectic or near eutectic composition of As-Te system upon heat treatment. Therefore, this paper reports the effects of annealing temperature on the structural and optical parameters of As30Te70 thin films. The bulk and thin films of 150 nm thick As30Te70 chalcogenide glasses were prepared by melt-quenching and thermal evaporation techniques, respectively. The glass transition and crystallization reactions of the bulk samples were investigated using differential scanning calorimetry (DSC). The influence of annealing temperature on the transformation of the crystal structure was studied by X-ray diffraction (XRD), while the surface morphology of the annealed samples was examined using scanning electron microscope (SEM). The optical band gap, refractive index and extinction coefficient were also calculated. The DSC scans showed that the melting temperature remains constant at 636.56 K. In addition, other characteristic temperatures such as the glass transition temperature, the onset crystallization temperature, and the crystallization peak temperature increase with increasing the heating rate. The crystalline phases for the as-prepared and annealed films consist of orthorhombic As, hexagonal Te, and monoclinic As2Te3 phases. Furthermore, the average crystallite size, strain, and dislocation density depend on the annealing temperature. The optical absorption results revealed that the investigated films have a direct transition, and their optical energy gap decreases from 1.82 eV to 1.49 eV as the annealing temperature increases up to 433 K. However, the refractive index, extinction coefficient, dielectric constant and the ratio of free carrier concentration to its effective mass, increase with increasing the annealing temperature.

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Thermal decomposition of Sn(II), Pb(II), Cd(II) and Hg(II) cross-linked metal-alginate complexes

El-Gahami M. A., Khairou K. S., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

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2003

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Vol. 51, No. 2

105-113

EN

The thermal decomposition of tin(II), lead(II), cadmium(II) and mercury(II) metal-alginate complexes has been studied using thermogravimetry (TG) and differential thermogravimetry (DTG) measurements. The TG curves showed three stages of weight loss, the DTG curves indicated the presence of a series of thermal stages associated with the TG curves. Dehydration of the coordinated water molecules occurred in the first stage, followed by decomposition of the dehydrated complexes in the next two stages. Thermal stability of these complexes in terms of the strength of chelation and coordination geometry is discussed.

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Diffusion controlled relaxation time and acceleration of velocity of sol-gel transformation for cross-linked metal alginate ionotropic gel comlexes

Khairou K. S., Al-Gethami W. M., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

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2003

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Vol. 51, No. 3-4

207-220

EN

The rate of gel-growth for spherical ionotropic metal alginate gel droplets has been studied. Experimental observations have shown that the relaxation time of the metal alginate ionotropic gel complexes of the droplet shapes decreased in the order Hg > Cd > Sn > Pb-alginates, whereas the velocity of sinking under gravitational acceleration decreases in the same order. The factors which affect the relaxation time and velocity of acceleration, such as the concentration and viscosity of the alginate sol, the nature and radius of the metal ion as well as the density and pH of the electrolyte solution have been examined. The activation energies indicated that the stability of these metal alginate gel complexes follows the order Hg > Cd > Pb ~ Sn alginates. A mechanism consistent with the experimental results has been discussed.

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Kinetics and mechanism of sol-gel transformation on polyelectrolytes of divalent metal-alginate gel complexes with formation of capillary ionotropic polymembranes

Khairou K. S., Al-Gethami W. M., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

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2002

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Vol. 50, No. 3

299-308

EN

The kinetics of gelation between Zn(II), Cd(II) and Pb(II) metal ion electrolytes and sodium alginate polysaccharide sol have been studied complexometrically at temperatures between 35 and 65°C. Using a large excess of alginate sol concentration, the pseudo first-order plots of exchange between Na+ counter ions of the macromolecular chains of alginate sol and the metal ions give sigmoidal curves with two distinct regions. The initial part was relatively fast and curved significantly at early times, followed by a slow decrease in the rates at longer times. The rate constants of gelation were found to show second-order overall kinetics and first-order in the concentration of both reac-tants. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.

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Kinetics and mechanism of reduction of hexachloroiridate (IV) by kojic acid in aqueous perchlorate solutions

Ahmed G. A. W., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

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2001

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Vol. 49, No. 3

235-244

EN

The kinetics of kojic acid reduction of hexachloroiridate (IV) in aqueous perchlorate solutions at constant ionic strength of 1.0 mol dm (-3) has been investigated spectrophotometrically. The reaction showed a first-order dependence in [IrCle]2" and a fractional-order with respect to kojic acid concentration. Kinetic evidence for the formation of an intermediate complex via free-radical mechanism is presented. The results obtained indicate that increasing the [H+] is accompanied by an appreciable acceleration of the rate of reaction at pH's< 0.4. The activation parameters have been evaluated and a tentative reaction mechanism consistent with the results is suggested.

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Kinetics and mechanism of redox reaction between ADA and hexachloroiridate (IV) in acid perchlorate solutions

El Korshy M. A., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 2

147-156

EN

The kinetics of hexachloroiridate (IV) oxidation of N-(2-acetamido) imino diacetic acid in aqueous perchloric acid solution at a constant ionic strength of 0:1 mol dm(-3) have been investigated spectrophotometrically. The reaction was found to be firstorder in [IrCl(6)2-, second-order in (ADA) and inverse fractional order with respect to (H+). Kinetic evidence for the formation of intermediate complexes between the substrate and iridium (IV) is presented. The activation parameters have been calculated and a tentative reaction mechanism consistent with the kinetics is discussed.