Enhanced Sensitivity of Epitaxial Graphene to NO2 by Water Coadsorption

Epitaxial graphene has shown a high sensitivity to NO2 down to ppb-level. However, the surrounding environment can strongly influence its sensing capability. Since water is naturally present in the atmosphere, understanding the effect of humidity on the gas sensitivity of epitaxial graphene is of paramount interest for creating novel gas sensors. Here, we show experimentally that epitaxial graphene exhibits an enhanced electrical response of a factor more than two for NO2 under humid condition compared to dry condition due to a strong enhancement of the hole doping of the graphene layer. Using electronic structure calculations, we explain the sensitivity enhancement by a water dipole screening of the graphene-NO2 dipole causing an increase of the charge transfer and consequently of the hole doping of the graphene layer.