Design Rules for One-Step Seeded Growth of Nanocrystals: Threading the Needle between Secondary Nucleation and Ripening

Abstract

The heterogeneous growth of inorganic shells on seed nanocrystals is used to synthesize heterostructured nanocrystals such as core@shell quantum dots for applications ranging from biological imaging to solid-state lighting. Control over shelling reactions can be achieved through continuous or layer-by-layer growth methods that are tedious and time-consuming, particularly for the growth of complex, multishell heterostructures. Here, we leverage high-throughput synthesis along with a library of precursors with tunable reactivity to develop a comprehensive understanding of the role of precursor reactivity, ligands, and temperature in one-step, seeded growth reactions on CdSe quantum dots. These experiments reveal a narrow range of precursor reactivity and monomer solubility that fosters the uniform, purely heterogeneous growth of shell material on the seed particles. This narrow “ideal growth” regime in experimental parameter space is sandwiched between opposing regimes that lead to secondary nucleation or ripening during growth. We also report that, at high concentrations of tri-n-octylphosphine, shell growth reactions exhibit “digestive ripening”, in which size distributions focus while particles dissolve. Coupled with kinetic simulations, these experiments reveal that the precursor reaction rate and monomer solubility are highly interdependent shell growth parameters that determine the balance between secondary nucleation and ripening. In contrast, the surface energy determines the evolution of the size and polydispersity of the heterostructures over time.