Modelling nanoscale cubic ZnS morphology and thermodynamic stability under sulphur-rich conditions

Abstract

Simultaneous reduction of the size and the degree of morphological polydispersivity in nanomaterials is critical for the overwhelming majority of nanotechnology applications. During synthesis, control over the size, phase and shape of crystalline nanoparticles is often achieved thermodynamically by regulating the temperature and pressure. However, a thorough understanding of the relationship between influential thermodynamic variables (such as temperature and pressure) and experimentally observed morphologies remains elusive. This is largely a result of the physical and technical challenges associated with characterisation and control at such small sizes. One way to overcome these obstacles is to construct a thermodynamic map of the equilibrium morphologies in the domain of the influential thermodynamic variables (a technique known as thermodynamic cartography). Here we employ a generalised shape-dependent thermodynamic model to predict the equilibrium morphology of cubic ZnS nanoparticles as a function of their size, and the temperature and partial pressure of sulphur. We describe a set of low energy shapes in a broad environmental context and identify thermodynamic regimes conducive to the formation of specific morphologies, before applying the technique to the study of some important non-equilibrium shapes. This study offers a useful guide for modifying experimental conditions to achieve synthesis aims and provides a means of maintaining post-synthesis structure through the prevention of unwanted phase and morphology transformations.