Spatial Dynamics of the Fermi Level in Electrolyte-Gated Graphene

TL;DR

This paper studies how electric fields affect graphene's Fermi level, revealing long-range effects due to graphene's low screening ability.

Contribution

A new experimental platform is introduced to study Fermi level dynamics in graphene using electrolyte microdroplets.

Findings

The Fermi level shifts sharply at the biased microdroplet interface and gradually equilibrates over tens of micrometers.

Graphene's low density of states limits its screening ability, causing long-range remote gating effects.

The Fermi level does not fully return to its undoped state within the observed range.

Abstract

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.

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