Water-Gated Charge Doping of Graphene Induced by Mica Substrates

TL;DR

This study reveals that water layers at the graphene/mica interface can modulate charge doping levels in graphene, with water effectively blocking charge transfer and enabling control of electronic properties.

Contribution

It demonstrates water-gated charge doping of graphene on mica substrates and shows how ultrathin water films influence doping levels and Fermi level modulation.

Findings

Mica induces strong p-type doping in graphene.

Ultrathin water films block interfacial charge transfer.

Water modulates graphene's Fermi level by 0.35 eV.

Abstract

We report on the existence of water-gated charge doping of graphene deposited on atomically flat mica substrates. Molecular films of water in units of ~0.4 nm-thick bilayers were found to be present in regions of the interface of graphene/mica hetero-stacks prepared by micromechanical exfoliation of kish graphite. The spectral variation of the G and 2D bands, as visualized by Raman mapping, shows that mica substrates induce strong p-type doping in graphene, with hole densities of $(9 \pm 2) \times 1012 cm${-2}$. The ultrathin water films, however, effectively block interfacial charge transfer, rendering graphene significantly less hole-doped. Scanning Kelvin probe microscopy independently confirmed a water-gated modulation of the Fermi level by 0.35 eV, in agreement with the optically determined hole density. The manipulation of the electronic properties of graphene demonstrated in this study should serve as a useful tool in realizing future graphene applications.