Cation Exchange during the Synthesis of Colloidal Type-II ZnSe-Dot/CdS-Rod Nanocrystals

Abstract

Cation exchange is known to occur during the synthesis of colloidal semiconductor heteronanoparticles, affecting their band gap and thus altering their optoelectronic properties. It is often neglected, especially when anisotropic heterostructures are discussed. We present a study on the role of cation exchange inevitably occurring during the growth of anisotropic dot-in-rod structures consisting of a spherical ZnSe core enclosed by a rod-shaped CdS shell. The material combination exhibits a type-II band alignment. Two reactions are compared: the shell-growth reaction of CdS on ZnSe and an exchange-only reaction of ZnSe cores to CdSe. Transmission electron microscopy and a comprehensive set of optical spectroscopy data, including linear and time-resolved absorption and fluorescence data, prove that cation exchange from ZnSe to CdSe is the dominant process in the initial stages of the shell-growth reaction. The degree of cation exchange before significant shell growth starts was determined to be about 50%, highlighting the importance of cation exchange during the heteronanostructure growth.

Temperature-Dependent Selection of Reaction Pathways, Reactive Species, and Products during Postsynthetic Selenization of Copper Sulfide Nanoparticles

“…For example, directed growth of CdS arms on a range of seeds occurs simultaneously with cation exchange of the core. 6,9 Selection between cation exchange and metal deposition on Cu 2−x Se follows design rules based on the compatibility of the lattice structures. 10,11 A particularly complex case reviewed by Kolny-Olesiak 12 nanostructures by acting as catalysts, seeds, or through cation exchange.…”

“…Ion exchange and directed growth processes, which are two of the most common methods for making heterostructured nanoparticles, often employ similar reagents and reaction conditions and thus can be in direct competition with one another. For example, directed growth of CdS arms on a range of seeds occurs simultaneously with cation exchange of the core. , Selection between cation exchange and metal deposition on Cu 2– x Se follows design rules based on the compatibility of the lattice structures. , A particularly complex case reviewed by Kolny-Olesiak details how copper sulfide precursors result in numerous hybrid nanostructures by acting as catalysts, seeds, or through cation exchange.…”