Fluctuation-induced tunneling conduction in iodine-doped bilayer graphene.

Intrinsic bilayer graphene is a semimetal. Upon applying an electric field, the potential difference between top and bottom layers can open an energy gap and tune bilayer graphene to an insulating state at the charge neutrality point. Here, we demonstrate that the properties of semimetallic bilayer graphene can be controllably tuned to either metallic or insulating by a simple way of iodine molecular doping. The transport properties of iodine-doped bilayer graphene have been systematically investigated. At high iodine doping concentrations, the Fermi level shifts by approximately 0.35 eV to the metallic region because of the symmetric doping on the top and bottom bilayer surfaces. At low iodine doping concentrations, small energy gaps open in local areas due to the asymmetric doping between the top and the bottom graphene layers. In this case, an insulating behavior at low temperatures is observed, which can be well explained by employing the fluctuation-induced tunneling (FIT) model. At medium iodine doping concentrations, both metallic and insulating behaviors can be observed at different temperatures, implying that both FIT and metallic mechanisms take effect. Our work may have potential applications in on/off controllable electronic devices, gas sensors, and transparent flexible electrode in optoelectronics. [ABSTRACT FROM AUTHOR]