Layer-Controlled Chemical Vapor Deposition Growth of MoS₂ Vertical Heterostructures via van der Waals Epitaxy

The fascinating semiconducting and optical properties of monolayer and few-layer transition metal dichalcogenides, as exemplified by MoS₂, have made them promising candidates for optoelectronic applications. Controllable growth of heterostructures based on these layered materials is critical for their successful device applications. Here, we report a direct low temperature chemical vapor deposition (CVD) synthesis of MoS₂ monolayer/multilayer vertical heterostructures with layer-controlled growth on a variety of layered materials (SnS₂, TaS₂, and graphene) via van der Waals epitaxy. Through precise control of the partial pressures of the MoCl₅ and elemental sulfur precursors, reaction temperatures, and careful tracking of the ambient humidity, we have successfully and reproducibly grown MoS₂ vertical heterostructures from 1 to 6 layers over a large area. The monolayer MoS₂ heterostructure was verified using cross-sectional high resolution transmission electron microscopy (HRTEM) while Raman and photoluminescence spectroscopy confirmed the layer-controlled MoS₂ growth and heterostructure electronic interactions. Raman, photoluminescence, and energy dispersive X-ray spectroscopy (EDS) mappings verified the uniform coverage of the MoS₂ layers. This reaction provides an ideal method for the scalable layer-controlled growth of transition metal dichalcogenide heterostructures via van der Waals epitaxy for a variety of optoelectronic applications.