Reversible Switching of Charge Transfer at the Graphene–Mica Interface with Intercalating Molecules

Understanding
and controlling charge transfer through molecular
nanostructures at interfaces is of paramount importance, particularly
for electronic devices but also for contact electrification or in
bioelectronics. We investigate the influence of intercalation and
exchange of molecularly thin layers of small molecules (water, ethanol,
2-propanol, and acetone) on charge transfer at the well-defined interface
between an insulator (muscovite mica) and a conductor (graphene).
Raman spectroscopy is used to probe the charge carriers in graphene.
While a molecular layer of water blocks charge transfer between mica
and graphene, a layer of the organic molecules allows for it. The
exchange of molecular water layers with ethanol layers switches the
charge transfer very efficiently from off to on and back. We propose
a charge transfer model between occupied mica trap states and electronic
states of graphene, offset by the electrostatic potentials produced
by the molecular dipole layers, as supported by molecular dynamics
simulations. Our work demonstrates how intercalation of molecules
of volatile liquids can reversibly affect charge transfer at interfaces.
This implies its strong impact on the function of hybrid inorganic–organic
electronic devices in different ambients and potential applications,
including sensors and actuators.