Prenucleation Clusters as Intermediates in Shell Development via Monomer Addition Onto Photoluminescent Quantum Dots

Colloidal semiconductor core/shell quantum dots (QDs) have promising potential in a wide range of optoelectronic applications. However, the pathway of shell formation remains elusive, impeding the applications. Here, we demonstrate for the first time that shell growth proceeds via monomer addition, similarly to the QD growth. Using CdS as a model shell system, we added individual Cd and S containing molecules to core QDs and found the appearance of CdS magic-size clusters (MSCs). We suggest that the added molecules experienced chemical self-assembly resulting in CdS prenucleation clusters (PNCs), which isomerized to the MSC. Afterward, the PNC transformed into monomers (Mos), which grew onto the core QD. Our work brings compelling evidence of the molecule-PNC-Mo-shell transition pathway, paving a new avenue to core/shell QDs upon the use of PNC samples and shaping a solid foundation on which the design and synthesis of functional nanomaterials with improved shell protection can be facilitated.