Eliminating Defect States in Monolayer Tungsten Diselenide by Coupling with a c-Plane Sapphire Surface.

Semiconducting transition metal dichalcogenides are promising platforms for exploring emergent two-dimensional (2D) exciton physics and constructing 2D optoelectronic devices. However, even in mechanically exfoliated and hexagonal boron nitride encapsulated samples that are expected to maintain the most intrinsic properties, shallow defect states are still unavoidable. Here, we reported a method for eliminating the defect states in monolayer WSe₂ by coupling it with a c-plane sapphire surface. We found that the defect-relevant photoluminescence peaks at cryogenic temperatures can be completely suppressed in WSe₂ on c-plane sapphire, resulting in intrinsic exciton radiation, prolonged lifetime, and increased diffusion length. Ab initio calculations revealed that the surface of c-plane sapphire is much more active than other planes, where oxygen atoms preferentially transfer to WSe₂ to repair selenium vacancy defects. Our Letter provides a new platform for defect engineering, which will promote the development of high-performance electronic and optoelectronic devices based on 2D materials.