Atomic-Scale Electric Potential Landscape across Molecularly Gated Bilayer MoS₂ Resolved by Photoemission

Electric gating in atomically thin field-effect devices based on transition-metal dichalcogenides has recently been employed to manipulate their excitonic states, even producing exotic phases of matter, such as an excitonic insulator or Bose–Einstein condensate. Here, we mimic the electric gating effect of a bilayer-MoS2 on graphite by charge transfer induced by the adsorption of molecular p- and n-type dopants. The electric fields produced are evaluated from the electronic energy-level realignment and Stark splitting determined by X-ray and UV photoelectron spectroscopy measurements and compare very well with literature values obtained by optical spectroscopy for similar systems. We then show that analysis of the inhomogeneous broadening and energy shifts of the quantum-well states of the valence band allows extraction of the full electric potential profile and charge-density redistribution across the entire heterojunction with atomic-scale precision, which is not accessible by other methods.