We present a full analytical theory of nanocrystal 'size focusing', a phenomenon in which injections of precursors at various quantities can generate monodisperse nanocrystals in solution. Nanocrystal applications in bio-imaging, sensors, and solar power all have stringent requirements on the size and polydispersity of the product nanocrystals. This investigation provides mathematical insight into how best to control the nanocrystal size distribution in a synthesis experiment. The primary results of the theory are (a) that size focusing is controlled explicitly by the rate of reaction of the precursor-to-monomer conversion, (b) that exquisite control of the size and polydispersity requires that the nucleation of nanocrystals must be separated (decoupled) from the growth process, and (c) that the presence of surfactants on the nanocrystals' surfaces will affect (i.e. either inhibit or even enhance) the maximum possible degree of size focusing. The resultant theory describes others' experimental results with qualitatively accuracy, but the real novelty of our analysis is that we recommend and inspire new methods for the synthesis of size-controlled nanocrystals, which have as yet remained unexplored. The predictions of the theory offer new avenues for experimental studies that can optimize and even help a priori to design new producesures for the production of monodisperse nanocrystals in solution.

Theory of nanocrystal size-focusing and how surfactants inhibit/enhance the effect

243rd National Meeting (2012)

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