Modelling polar wurtzite ZnS nanoparticles: the effect of sulphur supersaturation on size- and shape-dependent phase transformations

Using ab initio thermodynamics and a shape-dependent thermodynamic model for the Gibbs free energy of a nanoparticle, we modelled wurtzite nanoparticles with polar surfaces to predict the equilibrium shape with respect to size, temperature and pressure. We explore the role of thermodynamics in shape selection, and compare the free energies of the equilibrium wurtzite shapes with zinc blende. The thermodynamically preferred wurtzite shapes are described, and conditions under which kinetics are likely to influence the shape are identified. We also describe experimental conditions which we believe to be conducive to the formation of specific wurtzite and zinc blende shapes, such as the supersaturation of sulphur in the synthesis environment and the terminating species of the polar surfaces. This study provides a valuable reference for determining exact experimental conditions for specific morphology targeted synthesis of ZnS nanomaterials and for ensuring their post-synthesis stability.