CdS-ZnS core-shell nanoparticle formation: Experiment, mechanism, and simulation

CdS-ZnS core-shell nanoparticles are synthesized in a series of water-in-oil microemulsion solutions with increasing microemulsion drop sizes. Shell formation was confirmed by observation of a red shift in the UV-vis absorption spectra. Nanoparticle diameter and shell thickness estimated independently from the spectra and from mass balance approximation are consistent with each other. A new two-stage mechanism of coreshell nanoparticle formation has been developed from the experimental findings that consists of coalescence-exchange of microemulsion drops with nucleation, growth, and coagulation of particles. Quantitative predictions from Monte Carlo simulation of this mechanism compares well with the temporal evolution of experimental mean nanoparticle diameter and shell thickness for most of the cases, except when the nature of water in the microemulsion drops is different from bulk water for very small drop size. An increase in both the core and core-shell nanoparticle diameter with drop size reflects the control of the microemulsion template structure on nanoparticle synthesis.