Quantifying Cation Exchange of Cd²⁺ in ZnTe: A Challenge for Accessing Type II Heterostructures

The kinetic parameters governing cation exchange between molecular Cd 2+ precursors and ZnTe nanorods is mapped out in detail to provide an all-inclusive rubric for tuning the rate and extent of cation exchange in this system—allowing for band gap tunability over a 1 eV range. Evaluation of cation exchange as a function of concentration, temperature, and time supports a mechanism involving initial, rapid Cd 2+ adsorption followed by a rate determining cation exchange step with a measured activation energy of 24 kJ/mol. Provided there is sufficient cadmium to occupy the available surface sites, the solution concentration of cadmium has little influence on the rate of cation exchange, allowing the system to be modeled using pseudo-first-order kinetics, with observed rates ranging from 0.03 × 10 –3 s –1 at 20 °C to 2.8 × 10 –3 s –1 at 240 °C. It is also demonstrated that, due to the ease of cation exchange in these systems, previous claims of ZnTe/CdSe heterostructures are more accurately described as alloys.