Aqueous Phase Synthesized CdSe Magic-Sized Clusters: Solution Composition Dependence of Adsorption Layer Structure

We report dispersion solution composition dependence of the adsorption layer structure and the physical and optical properties of aqueous phase-synthesized semiconductor nanoparticles (NPs). We synthesized cysteine (Cys)-capped CdSe NPs with well-defined core structures, dispersed them in a series of aqueous solutions with different compositions, and then investigated their adsorption layer structure and physical and optical properties. Each CdSe NP consisted of a (CdSe)₃₃ or (CdSe)₃₄ magic-sized cluster (d ∼ 1.45 nm) core, a ligand-Cys shell, and an adsorption layer. The dispersion solution composition strongly affected the adsorption layer structure of the CdSe NPs. The solution with a composition close to that of the as-prepared solution stabilized the physical and optical properties of the NPs. The solution with a composition different from that of the as-prepared solution, however, resulted in large changes in their adsorption layer structure and thus their physical and optical properties. The solution composed of neutral or weakly charged Cys and Cd-Cys complexes led to the adsorption layer with low charge density and that destabilized the NPs. The solution containing only neutral or weakly charged forms of Cys, without Cd-Cys complexes, was favorable to the formation of a thick adsorption layer with low charge density and that destabilized the NPs. The amount of adsorbed Cys in the adsorption layer depended on the dispersion solution composition. However, the amount of adsorbed Cd-Cys complexes in the adsorption layer was almost constant regardless of the dispersion solution composition.