In Situ Monitoring of Cation-Exchange Reaction Shell Growth on Nanocrystals

Abstract

We demonstrate how in situ monitoring of the photoluminescence during shell growth around colloidal nanocrystals (NCs) can be used to develop a detailed and quantitative model for this process. We apply it here to study cation-exchange based growth of ZnS on a Cu–In–Se NC to form Cu–In–Se/ZnSe1–xSx alloyed NCs. We determine that this process begins with the Zn precursor binding to the outer layer of the NC followed by diffusion of Zn cations into successive atomic monolayers of the NC. At temperatures below 100 °C, Zn cations can only diffuse into the outermost atomic monolayer of the Cu–In–Se NCs. At growth temperatures above 100 °C, the second monolayer also becomes thermally accessible and can be filled with Zn cations. Our results provide an understanding of cation-exchange shell growth at the atomic level via optical analysis. The approach and mathematical model described here can be applied to other core/shell nanostructures and allows selection of optimal synthesis conditions to achieve desired cor...