Lack of a bandgap limits the utilization of graphene in nanoelectronic and nanophotonic devices. It is shown that a tunable bandgap of up to ≈0.2 eV can be engineered by controlled adsorption of water molecules to a graphene surface. The effect is reversible, and the energy gap reduces to ≈0.029 eV as the humidity is brought down to zero.
Koratkar’s team demonstrated how to open a band gap in graphene based on the amount of water they adsorbed to one side of the material, precisely tuning the band gap to any value from 0 to 0.2 electron volts. This effect was fully reversible and the band gap reduced back to zero under vacuum. The technique does not involve any complicated engineering or modification of the graphene, but requires an enclosure where humidity can be precisely controlled.
We study the electronic transport properties of dual-gated bilayer graphene devices. We focus on the regime of low temperatures and high electric displacement fields, where we observe a clear exponential dependence of the resistance as a function of displacement field and density, accompanied by a strong nonlinear behavior in the transport characteristics. The effective transport gap is typically 2 orders of magnitude smaller than the optical band gaps reported by infrared spectroscopy studies. Detailed temperature dependence measurements shed light on the different transport mechanisms in different temperature regimes.