Facilitating Uniform Large-Scale MoS 2 , WS 2 Monolayers, and Their Heterostructures through van der Waals Epitaxy.

The fabrication process for the uniform large-scale MoS 2 , WS 2 transition-metal dichalcogenides (TMDCs) monolayers, and their heterostructures has been developed by van der Waals epitaxy (VdWE) through the reaction of MoCl 5 or WCl 6 precursors and the reactive gas H 2 S to form MoS 2 or WS 2 monolayers, respectively. The heterostructures of MoS 2 /WS 2 or WS 2 /MoS 2 can be easily achieved by changing the precursor from WCl 6 to MoCl 5 once the WS 2 monolayer has been fabricated or switching the precursor from MoCl 5 to WCl 6 after the MoS 2 monolayer has been deposited on the substrate. These VdWE-grown MoS 2 , WS 2 monolayers, and their heterostructures have been successfully deposited on Si wafers with 300 nm SiO 2 coating (300 nm SiO 2 /Si), quartz glass, fused silica, and sapphire substrates using the protocol that we have developed. We have characterized these TMDCs materials with a range of tools/techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), micro-Raman analysis, photoluminescence (PL), atomic force microscopy (AFM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and selected-area electron diffraction (SAED). The band alignment and large-scale uniformity of MoS 2 /WS 2 heterostructures have also been evaluated with PL spectroscopy. This process and resulting large-scale MoS 2 , WS 2 monolayers, and their heterostructures have demonstrated promising solutions for the applications in next-generation nanoelectronics, nanophotonics, and quantum technology.