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, WS transition-metal dichalcogenides (TMDCs) monolayers, and their heterostructures has been developed by van der Waals epitaxy (VdWE) through the reaction of MoCl or WCl precursors and the reactive gas HS to form MoS or WS monolayers, respectively. The heterostructures of MoS/WS or WS/MoS can be easily achieved by changing the precursor from WCl to MoCl once the WS monolayer has been fabricated or switching the precursor from MoCl to WCl after the MoS monolayer has been deposited on the substrate. These VdWE-grown MoS, WS monolayers, and their heterostructures have been successfully deposited on Si wafers with 300 nm SiO coating (300 nm SiO/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/WS heterostructures have also been evaluated with PL spectroscopy. This process and resulting large-scale MoS, WS monolayers, and their heterostructures have demonstrated promising solutions for the applications in next-generation nanoelectronics, nanophotonics, and quantum technology.