Topotactic Growth of Edge-Terminated MoS 2 from MoO 2 Nanocrystals

Layered transition metal dichalcogenides have distinct physicochemical properties at their edge-terminations. The production of an abundant density of edge structures is, however, impeded by the excess surface energy of edges compared to basal planes and would benefit from insight into the atomic growth mechanisms. Here, we show that edge-terminated MoS nanostructures can form during sulfidation of MoO nanocrystals by using in situ transmission electron microscopy (TEM). Time-resolved TEM image series reveal that the MoO surface can sulfide by inward progression of MoO (202̅):MoS (002) interfaces, resulting in upright-oriented and edge-exposing MoS sheets. This topotactic growth is rationalized in the interplay with density functional theory calculations by successive O-S exchange and Mo sublattice restructuring steps. The analysis shows that formation of edge-terminated MoS is energetically favorable at MoO (110) surfaces and provides a necessary requirement for the propensity of a specific MoO surface termination to form edge-terminated MoS . Thus, the present findings should benefit the rational development of transition metal dichalcogenide nanomaterials with abundant edge terminations.