Favoring the Growth of High-Quality, Three-Dimensional Supercrystals of Nanocrystals

A recently developed emulsion-templated assembly method promises the scalable, low-cost, and reproducible fabrication of hierarchical nanocrystal (NC) superstructures. These superstructures derive properties from the unique combination of choice of NC building blocks and superstructure morphology, and therefore realize the concept of `articial solids'. To control the nal properties of these superstructures, it is essen- tial to control the assembly conditions yielding distinct architectural morphologies. Here, we explore the phase-space of experimental parameters describing the emulsion- templated assembly including: temperature, interfacial tension, and NC polydispersity, and demonstrate which conditions lead to the growth of the most crystalline NC su- perstructures, or supercrystals. By using a combination of electron microscopy and small-angle X-ray scattering, we show that slower assembly kinetics, softer interfaces, and lower NC polydispersity contribute to the formation of supercrystals with grain sizes up to 600nm, while reversing these trends yields glassy solids. These results pro- vide a clear path to the realization of higher-quality supercrystals, necessary to many applications.