Fabricating model heterostructures of large-area monolayer or bilayer MoS2 on an Au(111) surface under ultra-high vacuum

Fabricating heterojunctions with precisely controlled interfacial structures is crucial for exploring novel low-dimensional physics and for realizing high-performance devices. However, such capabilities are often constrained by contamination from the ambient environment or by the limitations of applicable methods and materials under vacuum conditions. In this study, MoS₂/Au(111) heterostructures were fabricated by exfoliating MoS₂ thin layers onto a crystallized Au(111) surface using a gold-assisted exfoliation method in an ultra-high vacuum environment. This method yields millimeter-sized monolayer or sub-millimeter-sized bilayers with contamination-free interfaces, which are unattainable for samples made in air. Scanning tunneling microscopy revealed that both the monolayer and the bilayer exhibit uniform and well-ordered moiré superlattices controlled by the twisting angle between the Au(111) surface and the MoS₂ overlayer. The direct contact with the Au surface renders the monolayer MoS₂ weakly metallic, while a less coupled bilayer is semiconducting, indicating a 0.54 eV Schottky barrier for the MoS₂/Au(111) contact. This method is applicable to various combinations of van der Waals materials and metal surfaces. The uniform and controllable heterojunctions can serve as ideal model systems for exploring semiconductor–metal interfaces and atomic structures formed within.