An in situ small angle X-ray scattering study of carboxylate ligand mediated growth of CdSe nanoplatelets.

Group II-VI semiconductor nanoplatelets (NPLs) have unique quantum confinement effects and large specific surface areas, offering distinct advantages in advanced optoelectronic devices, catalysis, and biomedical sensing. Carboxylate ligands are widely used in NPL synthesis; however, their roles in the synthesis process remain insufficiently understood. Herein, we systematically investigated the formation process of CdSe NPLs via a one-pot method using carboxylate ligands with different chain lengths and proportions. We found that ligand chain length can significantly influence the NPL formation. The ratio of short- to long-chain ligands governs the nucleation, growth pathway and final NPL morphology. For a low proportion of short-chain ligands, elongated NPLs formed during nucleation and subsequently underwent lateral expansion, yielding flat NPLs with high aspect ratios. In contrast, a high proportion of short-chain ligands resulted in the formation of dot-shaped nanocrystals during nucleation, which subsequently dissolved, accompanied by the gradual formation of NPLs with low aspect ratios and a curved morphology. We propose that these observations are associated with competitive interactions between short- and long-chain ligands at the nanocrystal surfaces. Short-chain ligands, due to weaker hydrocarbon chain interactions, promote lateral growth, whereas long-chain ligands preferentially inhibit lateral expansion. This study provides new insights into the formation mechanism of CdSe NPLs and facilitates morphology control and the practical application of related nanomaterials.