Identification and Growth Mechanism of ZnS Nanoparticles with Mixed Cubic and Hexagonal Stacking

Nano-ZnS with mixed cubic and hexagonal stacking was synthesized via reaction of zinc acetate with thioacetamide in a weakly acidic solution, while nano-ZnS in primarily the sphalerite phase was synthesized in a basic solution. X-ray diffraction (XRD) and transmission electron microscopy were used to characterize the nanoparticle structures. The formation of nano-ZnS with mixed stacking was simulated numerically by generation of ZnS nanoparticles via random cubic and hexagonal stacking of the close packing layers. The numerically simulated stacking distribution is determined by the ratio of the probability of cubic vs hexagonal stacking. XRD patterns of ZnS nanoparticles with mixed stacking were simulated by using Debye function analysis. The wurtzite (102) peak is absent whereas the wurtzite (103) peak is present in nano-ZnS with mixed stacking, matching features of XRD results for synthesized ZnS. We conclude that crystallization of ZnS nanoparticles with mixed stacking occurs via a growth mechanism in which sequential addition of hexagonal vs. cubic stacked layers occurs with equal probability. The approach may be used for analysis of mixed stacking in other nanomaterials with related structures, such as CdS and CdSe.