Effect of the Synthesis Method on the Formation, Surface State, and Optical Properties of Colloidal CdSe Nanoplatelets

Abstract

The development of approaches for controlling the thickness, structural uniformity, and surface chemical state of CdSe nanoplatelets is important for obtaining materials with tailored and reproducible spectroscopic characteristics. This work presents a comparative study of CdSe nanoplatelets synthesized by gradual heating using pre-synthesized cadmium myristate and by hot injection of an organoselenium precursor into a reaction medium containing cadmium acetate and oleic acid. The selected synthesis method was shown to have a pronounced effect on the formation process, thickness, and uniformity of the nanoplatelets. Under gradual heating, nanoplatelet formation is preceded by the appearance of intermediate CdSe-containing nanoparticles, while the final product consists predominantly of 4 ML nanoplatelets with a minor fraction of 3 ML species. The hot-injection method yields a more uniform population of 3 ML nanoplatelets. In both samples, the formation of a cubic sphalerite-type CdSe structure was confirmed, whereas the sample obtained by gradual heating exhibited more pronounced structural heterogeneity. Differences in nanoplatelet thickness and uniformity are reflected in their optical properties and surface state. Analysis of the carboxylate groups and elemental composition indicates differences in the local environment of the surface ligands and suggests the probable presence of a residual cadmium–myristate component in the sample synthesized using cadmium myristate. The results demonstrate that the nature of the cadmium precursor, the mode of formation of its carboxylate species, and the selenium introduction conditions jointly determine the structural, surface, and spectroscopic characteristics of CdSe nanoplatelets.