Nucleation and Growth of ZnSe Quantum Dots from Prenucleation Clusters in Dispersion at Room Temperature

Abstract

Little is known about the nucleation and growth (N/G) of colloidal semiconductor quantum dots (QDs) from prenucleation clusters (PNCs) in dispersion at room temperature. Here, we show that when a pre-heated sample of ZnSe (containing the PNC and no QDs) is dispersed, the N/G of QDs occurred. When the sample is added to a dispersion of ZnSe QDs, the QDs either became larger or kept intact with smaller QDs seen. The growth of QDs is associated with monomer addition and QD dissolution sometimes, the two intrinsic energy barriers of which increase with the QD size. We use two temperatures, T2 and T1, to symbolize the two barriers, respectively. T2 is smaller than T1. Our findings suggest that with monomers provided by the PNC, QDs grow in a size-focusing regime with T2 smaller than 25 °C (T3); when T2 is larger, the N/G of smaller QDs occurs. When the PNC is consumed completely, QDs grow in a size-defocusing regime (Ostwald ripening) with T1 smaller than 25 °C (T3); as T1 approaches 25 °C (T3), QDs stop growing. Our study brings a fundamental understanding of the PNC that plays a significant role in the size and size distribution of QDs.