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In the present study ZnSe quantum dots (QDs) were synthesized by chemical co-precipitation method using mercaptoethanol as the capping agent. These nanostructures were characterized for structure and surface morphology by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectrometry respectively. The average size of ZnSe quantum dots from XRD and HRTEM is found to be 4-5 nm having cubic crystalline phase. Effect of annealing temperature, which were determined as phase transformation temperatures (299 and 426 °C) using differential scanning calorimetry has been investigated for structural and thermal stability of QDs. The XRD of annealed samples at temperatures 325 and 442 °C (slightly higher than the temperatures corresponding to two crystallization peaks in the DSC scan) have been carried out to find structural changes corresponding to these annealing temperatures. Sample annealed at 325 °C showed no change in the phase except improvement in intensity of peaks (crystallinity) whereas sample annealed at 442 °C showed transitions from cubic phase of ZnSe to ZnO and orthorhombic phases of ZnSeO, ZnSeO. Emergence of ZnO peaks in the XRD pattern of annealed samples have been further verified by Raman spectroscopy of the annealed samples. Besides this crystallization kinetics of ZnSe quantum dots has been employed to determine activation energies of these transitions due to oxidation by employing Kissinger, Augis Bennett and Ozawa's models. Higher activation energy of crystallization corresponding to first crystallization peak shows that the cubic phase is more thermally stable. [ABSTRACT FROM AUTHOR]

Ge30-xSe70Snx (8≤x≤20) glasses have been prepared using conventional melt quenching. The kinetics of the glass transition have been studied in terms of the variation of glass transition temperature with composition and heating rate. In addition the activation energy of the glass transition (Et) and its compositional dependence have been investigated using the Kissinger approach. The thermal stability of these glasses has been investigated using different stability parameters such as the kinetic resistance ΔT (Tc-Tg), the weighted thermal stability parameter H' ((Tc-Tg)/Tg) and S ((Tc-Tg) (Tp-Tc)/Tg) in terms of glass transition temperature (Tg), crystallization onset temperature (Tc) and peak crystallization temperature (Tp). It has been found that the thermal stability decreases with the increasing Sn content in the glassy alloys. A glassy sample is more stable if it has a higher kinetic resistance to crystallization. Accordingly, it has been observed that Ge22Se70Sn8 glassy sample is more thermally stable compared to the other members of the series. [ABSTRACT FROM AUTHOR]

CdSe quantum dots (QDs) having size 3-5 nm have been synthesized by chemical co-precipitation method in mixed amorphous and cubic phase. These QDs have been characterized by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FTIR) spectrometry. Cubic phase is confirmed by XRD and amorphous phase have been found using differential scanning calorimetry (DSC). The thermal analysis carried out by using DSC at different heating rates shows endothermic and exothermic peaks at different temperatures corresponding to their glass transition and different crystalline phases. The cubic phase of the crystalline CdSe obtained at 261 °C in the DSC scan of as prepared sample start transforming to stable hexagonal phase of CdSe corresponding to second crystallization peak 317 °C in DSC thermogram. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) have also been used to determine the crystallization temperature (257 °C) and weight loss in the temperature range 220-267 °C. Activation energies corresponding to two exothermic peaks (cubic and hexagonal phase) have been determined by employing different theoretical models. Lower activation energy of the hexagonal phase corresponding to second exothermic peak obtained at higher temperature in the DSC thermogram shows the higher thermal stability of this phase and could be employed for preparing a material to improve the performance of memory devices, solar cells etc. [ABSTRACT FROM AUTHOR]

A review of the recent work on II-VI semiconducting nanoparticle-polymer nanocomposites is presented. This review is not comprehensive but provides an overview of the processing techniques, trends in mechanical and thermal behaviuor and morphology of nanocomposites. A number of composite systems with amorphous polymer matrices and different nano-sized filler materials are discussed. [ABSTRACT FROM AUTHOR]