Kinetic-Dependent Crystal Growth of Size-Tunable CdS Nanoparticles

Abstract

The general study of crystal growth of spherical-like nanoparticles involves monitoring the kinetics during the progress of the reaction. In the case of cadmium sulfide (CdS), cadmium acetate and sodium sulfide are employed as starting reagents that are dissolved in different solvents (ethylene glycol, glyme, diglyme, and trioctylphosphine) to study the solvent effect on monomers, nucleation rates, and the quality of the seeds. Trialkylphosphine oxide (alkyl = ethyl or octyl) is chosen as a surfactant to passivate the surface of CdS nanoparticles. We propose a kinetic approach model to illustrate the unreported time-evolved crystal growth mechanism observed in this case. An experimental value for the diameter of critical volume (Vc), a nanosized volume with a relative minimum surface-volume tension and considered a temporal stable stage (r = 5.7 nm in this case), is derived from transmission electron microscopy images. The size of the nanoparticles made by this synthesis route is tunable by variation of the reaction time and control of the reaction temperature; in addition, the resulting sizes are suitable for spectroscopic testing of electron quantum confinement. The X-ray powder diffraction data are consistent with a pure hexagonal CdS lattice and show no evidence for a mixed phase involving cubic symmetry.