We present a general strategy for a facile synthesis of complex multifunctional nanoscale materials via colloidal atomic layer deposition (c-ALD). The c-ALD technique is based on self-limiting half-reactions of ionic precursors on the surface of a nanocrystal (NC) occurring at room temperature. Using this technique, uniform layers of CdS and ZnS semiconductor shells were epitaxially grown on CdSe semiconductor cores with different shell combinations, leading to the precise control of the optical properties of these heterostructures. All core-shell multicomponent nanoparticles preserve narrow size distributions, phase crystallinity, and shape homogeneity of the initial NCs. Furthermore, we attempted to extend the toolbox of the c-ALD to combine materials with intrinsically different properties, such as Au/CdS core/shell structures with substantial lattice mismatch. The results presented in this work demonstrate great opportunities for creating functional materials with programmable properties for electronics and optoelectronics
We investigated the growth kinetics of CdSe nanocrystals for a hot-injection colloidal synthesis, as a function of selected key process parameters. In this investigation, the synthesis consisted in the injection of trioctylphosphine-selenium into cadmium oleate, followed by nucleation and growth stages. The evolution of size and size distribution of the nanocrystals was monitored during the synthesis via UV−visible absorption and photoluminescence spectroscopy. Three growth parameters have been extracted from the experimental data through a general kinetic growth model, and discussed: the initial particle size, the growth rate, and the particle size at the end of the growth. A modification of the classical nucleation theory has been developed to explain and predict the equilibrium (final) size of the nanoparticles, by taking into consideration the consumption of monomers during crystal formation and growth. The model accurately predicts the trends of the crystal size as a function of the oleic acid concentration. The model represents a valuable tool for the study of colloidal crystal growth providing new insight into the physical and chemical processes behind the nucleation and growth. Moreover, it enables exploration of new limits in terms of typical synthetic conditions, aiming at the optimization of the synthesis yield for every single case at handa very important goal in view of the ever-growing need for large-scale fabrication of colloidal nanostructures.
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