Vertical Heterostructures of Layered Metal Chalcogenides by Van Der Waals Epitaxy for Solar Energy Conversion and Catalysis

We report a facile chemical vapor deposition (CVD) growth of vertical heterostructures of layered metal dichalcogenides (MX₂) enabled by van der Waals epitaxy for the first time. Few layers of MoS₂, WS₂, and WSe₂ were grown uniformly onto microplates of SnS₂ under mild CVD reaction conditions and the heteroepitaxy between them was confirmed using cross sectional transmission electron microscopy (TEM) and unequivocally characterized by resolving the large-area Moiré patterns appeared on the basal planes of microplates. Additional photoluminescence peaks were observed in heterostructures of MoS₂-SnS₂, which can be understood with electronic structure calculations to likely result from electronic coupling and charge separation between MoS₂ and SnS₂ layers. This work opens up the exploration of novel large-area heterostructures of diverse MX₂ nanomaterials as the material platform for electronic structure engineering of atomically thin two-dimensional (2D) semiconducting heterostructures and novel device applications, such as in solar energy conversion.  Furthermore, by controlling the nanostructures and polymorphs of group 6 MX₂ (M = Mo, W; X = S, Se) materials, we have significant enhanced their catalytic activity in hydrogen evolution reaction for photoelectrochemical water splitting.