Manipulation of the two-dimensional hydrogenic defect states in monolayer MoS₂

In-depth understanding of the charged object in atomic-scale is crucial for both fundamental science and unprecedented functional applications such as ultrasmall memory devices. Here, we demonstrate a reversible switching of hydrogenic states of charged defects in MoS₂ monolayer employing scanning tunneling microscopy and spectroscopy (STM/S). Bistable charge states of the defects are identified: negatively charged (-1) and neutral (0), where they can be switched reversibly via STM tip manipulation. The negative charge state is characterized by the presence of the upward band bending and resulting depletion region in vicinity of the defects. The Coulomb potential of the negative charged perturbation is renormalized via dielectric screening of the host two-dimensional semiconducting MoS2, which admits additional localized states near the valence band side. Thus, by controlling the defect charge, we “switch on” or “off” the in-gap states. We show that the observed in-gap states are the physical manifestation of the two-dimensional Rydberg states.