Nanoagregados em matrizes vitreas

AUTOR(ES)

Guinther Kellermann

DATA DE PUBLICAÇÃO

2003

RESUMO

In this thesis we studied the formation and growth of nanoclusters in supersa-turated glassy matrixes during isothermal annealing. We investigate: (i) the effects of sulfur content and of a thermal pre-treatment on the formation and growth of CdTe1-x Sx nanocrystals in a borosilicate glass matrix; (ii) the formation and growth of PbTe nanocrystals in a silicate glass; and (iii) the formation and growth of liquid Bi nanodroplets in a soda-borate glass. These studies were performed by in situ small angle X-ray scattering (SAXS) measurements during annealing of the glasses. From the SAXS experiments we determine the size distribution function, average size, size dispersion, fraction of the total volume and number per unity volume of the nanoclusters (nanocrystals or nanodroplets). The dependence of these parameters with the annealing time was compared with the predictions of classical theories, and so, the mechanisms involved in different stages of the process were determined. In addition, we investigate the crystal-to-liquid transition of Bi nanocrystals em-bedded in a soda-borate glass. Simultaneous wide and small angle X-ray scattering measurements (WAXS and SAXS, respectively) at different temperatures in the range from room temperature up to above the temperature where the nanocrystals are completely melted allowed us to determine the dependence between the melting temperature and the nanocrystal radius. The results were compared with the ob-tained in previous works and with the dependence predicted by a theoretical model that describes the melting of small spherical crystals based on simple thermodynamic arguments. We also briefly describe the Brazilian Synchrotron Light Laboratory (LNLS) SAXS beamline and a high temperature chamber specially designed for in situ si-multaneous WAXS and SAXS experiments

ASSUNTO(S)

raios x - espalhamento a baixo angulo materiais nanocompositos nanocristais

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