Microscopic Investigations of Point Defect Interactions in WS2 Monolayers

Atomic point defects provide an alternative tuning knob for engineering the properties and functionality of 2D transition metal dichalcogenides (TMDs). Prior to engineering point defects to tailor material properties, identification and investigation of their electronic structure is key to their implementation for device applications. The two most common atomic point defects in monolayer WS₂ are sulfur vacancies and oxygen substituents, which have been thoroughly reported on, but their interaction has yet to be investigated. Here, we report a scanning tunneling microscopy/spectroscopy study of the interaction between these two common point defects. We reveal the appearance of an occupied in-gap state (OIGS) at the sulfur vacancy site, V_S, resulting from its interaction with local oxygen substituents, O_S. The energy location of the OIGS is a strong function of the local O_S density. With the aid of ab initio calculations, we unveil that the sulfur vacancy OIGS originates from the Γ -valley modification of the tungsten d- and sulfur p-orbital hybridization.