Revisiting the ZnO Q?dot Formation Toward an Integrated Growth Model

Reference Presenter Authors
06-030 Celso Valentim Santilli Caetano, B.L.(Instituto de Quimica/UNESP); Briois, V.(Synchrotron Soleil); Meneau, F.(LNLS); Pulcinelli, S.H.(Instituto de Química/UNESP - Araraquara); Santilli, C.V.(Instituto de Química/UNESP - Araraquara); The nucleation, growth and aggregation of ZnO nanocrystals were unambiguously unravelled and associated with de?ned families of quantum dots and well described from two kinetic models: coalescence and Ostwald ripening. The in situ monitoring by X-ray absorption spectroscopy combined with UV?vis spectroscopy allows the determination of the time evolution of the proportions of each family of quantum dots of characteristic sizes from a multivariate data analysis. The aggregation index was calculated from combined UV?vis absorption and small-angle X-ray scattering measurements. The growth of single quantum dot nucleus results from coalescence by pure oriented attachment between themselves, then aggregation occurs through the welding of adjacent coalesced nanocrystals. At the advanced stage the quantum dot coarsening follows the Ostwald ripening mechanism. From the higher oriented attachment e?ciency observed here as compared with earlier reported studies using NaOH and KOH, we propose a uni?ed mechanism to describe the coalescence and coarsening of ZnO nanocrystals based on the shielding caused by the adsorption of the alkali solvated cations around the nanocrystals. This latter shielding e?ect has been also proved to be very e?cient for the preparation of quantum dot powder with controlled size as demonstrated by X-ray di?raction and transmission electron microscopy.

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