Evidence of Magic-Size Cluster, Nanorod, and Nanoleaflet Intermediates During the Growth of CdSe Nanoplatelets

Colloidal semiconductor nanoplatelets (NPLs) exhibit exceptional optical properties due to their atomically defined thickness, yet the understanding of their formation pathways remains incomplete. Here, we uncover a sequential growth mechanism for CdSe NPLs by isolating previously hidden intermediates. Using phosphines to slow reaction kinetics, we capture direct evidence that magic-size clusters fuse into nanorods, which then give rise to nanoleaflet-like intermediates that expand laterally and ultimately evolve into fully developed nanoplatelets. We show that free phosphines regulate both dimensionality and monolayer thickness, with high concentrations arresting growth entirely. These findings provide the first identification of nanoleaflets (NLFs) as critical intermediates and establish a mechanistic framework that connects zero-, one-, and two-dimensional species during NPL formation. This work advances a deeper understanding of NPL growth and offers new strategies for rationally designing atomically precise 2D nanomaterials.