Wyniki wyszukiwania - BazTech

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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.

2

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.

3

Generalizations of two-index two-variable Hermite matrix polynomials

Metwally M., Mohamed M., Shehata A.

Demonstratio Mathematica

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2009

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Vol. 42, nr 4

687-701

EN

In this paper, we introduce a new generalization of the Hermite matrix polynomials expansions of some relevant matrix functions appearing in the solution of differential systems. An explicit representation and an expansion of the matrix exponential in a series of these matrix polynomials is obtained. Properties of Hermite matrix polynomials such as the recurrence formula permit an efficient computations of matrix functions are established. A new expansions of the matrix exponential for a wide class of matrices in terms of Hermite matrix polynomials is proposed.

4

Experimental and Theoretical Studies on Pyrolysis of O-Acetyl Derivatives of beta-phenylcinnamaldehyde and Benzaldehyde Oximes

Mohamed M., Siedlecka M., Suwiński J.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 5

577-590

EN

[ReBr3(py)3]0.42[ReBr2(NO)(py)3]0.58 (1), trans-[ReBr4(OPPh3)2] (2), [ReBr(NO)(dppe)2]Br (3) and orthorhombic polymorph of mer-cis- [Re(NO)Br3(OPPh3)2] (4) complexes have been synthesized by reactions of monoclinic polymorph of mer-cis-[Re(NO)Br3(OPPh3)2] with pyridine, bis(diphenylophosphino) ethane, 2,2_-bipyridine, 1,10-phenanthroline. The NO group in 1 and 4 is coordinated in a linear way. Due to nitrosyl/bromine compositional disorder, the shortening of Re-NO distance [1.68(5) A] and the elongation of N-O bond length [1.38(10) A] are observed in1. The N-O bond length in 4 is extremely short [0.94(1) A], which results probably from steric interactions of two mutually cis OPPh3 molecules and a large discrepancy of Re-O-P angle values.

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Tandem pericyclic reactions in synthesis of azines. Part I. PM3 study of thermal behavior of 1-aza-1,3,5-hexatrienes

Suwiński J., Mohamed M.

Zeszyty Naukowe. Chemia / Politechnika Śląska

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2002

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z. 147

5-13

EN

This paper presents results of PM3 calculations of the disrotatory thermal electrocyclization of several simple azahexatrienes and a short review of selected papers concerning formation of azines in thermal processes starting from aza-1,3,5-hexatriene derivatives and occurring, we believe, as tandem pericyclic processes involving disrotatory electrocyclization followed by a concerted elimination or other thermal reactions. The results of calculations in some cases support the mechanistic propositions based on the results of synthetic experiments, in the other ones they seem to deny them, pointing out to pericyclic processes.

PL

W pracy przedstawiono wyniki obliczeń metodą PM3 dysrotacyjnej termicznej elektrocyklizacji szeregu prostych azaheksatrienów i krótki przegląd wybranych prac dotyczących tworzenia azyn w termicznych procesach wychodząc z aza-1,3,5-heksatrienu lub jego pochodnych i zachodzących, jak sądzimy, zgodnie z mechanizmem dysrotacyjnej elektrocyklizacji wraz z następczą uzgodnioną eliminacją lub innym termicznym procesem. Wyniki naszych obliczeń w niektórych przypadkach potwierdzają mechanizmy proponowane na podstawie eksperymentów, w innych wydają się im zaprzeczać, wskazując na procesy pericykliczne.