Structure analysis on the nanoscale: closed WS2 nanoboxes through a cascade of topo- and epitactic processes

Abstract

Closed WS₂ nanoboxes were formed by topotactic sulfidization of a WO₃/WO₃·⅓H₂O intergrowth precursor. Automated diffraction tomography was used to elucidate the growth mechanism of these unconventional hollow structures. By partial conversion and structural analysis of the products, each of them representing a snapshot of the reaction at a given point in time, the overall reaction can be broken down into a cascade of individual steps and each of them identified with a basic mechanism. During the initial step of sulfidization WO₃·⅓H₂O transforms into hexagonal WO₃ whose surface allows for the epitaxial induction of WS₂. The initially formed platelets of WS₂ exhibit a preferred orientation with respect to the nanorod surface. In the final step individual layers of WS₂ coalesce to form closed shells. In essence, a cascade of several topotactic reactions leads to epitactic induction and formation of closed rectangular hollow boxes made up from hexagonal layers.