Spatial Dynamics of the Fermi Level in Electrolyte-Gated Graphene

Understanding how electric fields propagate in nanomaterials is essential for optimizing their performance in electronic, energy, and sensing devices that require precise control of charge carrier density. We use in situ Raman spectroscopy combined with local voltage application via an electrolyte microdroplet to investigate the Fermi level dynamics in monolayer graphene. We observe a sharp initial shift of the Fermi level toward the charge-neutral Dirac point when crossing the biased microdroplet interface to the adjacent unbiased graphene, followed by a gradual equilibration extending tens of micrometers. Notably, the Fermi level does not fully recover to its undoped state within this range. We attribute these long-range, remote gating effects to the intrinsically low density of states of graphene, which limits its ability to screen the electric field, allowing the potential to equilibrate gradually beyond the biased region. This work introduces a robust and broadly applicable experimental platform with practical implications for semiconducting and semimetallic electronic devices.