Colloidal nanocrystal synthesis allows for an unprecedented ability to precisely tune composition, crystal phase and particle morphology across a vast array of compounds. However, the reaction pathways from precursor decomposition to particle formation that underpin nucleation and growth are yet not fully understood. In this talk, our recent progress on understanding the nucleation and growth kinetics in colloidal multinary nanocrystals using in-situ X-ray absorption and double aberration-corrected scanning TEM will be discussed.
First, we present a real-time investigation of the formation of colloidal CZTS nanorods by in situ X-ray absorption spectroscopy and small angle X-ray scattering.1 Using this x-ray combination, we are able to unravel the key nucleation and growth stages in CZTS nanocrystal synthesis. The findings of our work show sequential occurrence of key reaction intermediates have a significant influence on reaction pathways. It further shows that in-situ monitoring of the progress from the precursor through these intermediates to particle formation can allow for remarkable new insights into nucleation and growth processes.
Further, through an ex-situ mechanistic study by aberration-corrected TEM, we demonstrate the evolution of compositionally homogenous Cu-Bi-Zn-S nanorods via a solution-liquid-solid growth mechanism. We discuss how the formation of Bi seed, bypassing the growth of Cu2-xS nuclei, resulted in Bi seeded Cu2-xS heterostructures. Later, these heterostructures evolved into (nanorods) via dissolution of the Bi rich seed and recrystallization of Cu-rich stem into the transitional segment formed at the hetero-interface followed by the incorporation of Zn2+. Such comprehensive investigation of the evolution of colloidal particle formation using x-ray spectroscopy and electron microscopy is widely applicable across all nanocrystal systems and can greatly expand our understanding on their formation.