Water on graphene: Review of recent progress

TL;DR

This review summarizes recent research on how water interacts with various types of graphene, affecting its electronic properties and highlighting the importance of environmental conditions in graphene-based device performance.

Contribution

It provides a comprehensive overview of water's effects on different graphene forms and emphasizes the need for precise environmental characterization in experiments.

Findings

Water withdraws electrons from graphene

Interaction depends on substrate and layer structure

Environmental conditions critically influence electrical properties

Abstract

The sensitivity of graphene to the surrounding environment is given by its {\pi} electrons, which are directly exposed to molecules in the ambient. The high sensitivity of graphene to the local environment has shown to be both advantageous but also problematic for graphene-based devices, such as transistors and sensors, where the graphene carrier concentration and mobility change due to ambient humidity variations. In this review, recent progress in understanding the effects of water on different types of graphene, grown epitaxially and quasi-free standing on SiC, by chemical vapour deposition on SiO2, as well as exfoliated flakes, are presented. It is demonstrated that water withdraws electrons from graphene, but the graphene-water interaction highly depends on the thickness, layer stacking, underlying substrate and substrate-induced doping. Moreover, we highlight the importance of clear and unambiguous description of the environmental conditions (i.e. relative humidity) whenever a routine characterisation for carrier concentration and mobility is reported (often presented as a simple figure-of-merit), as these electrical characteristics are highly dependent on the adsorbed molecules and the surrounding environment.