1. Tuning the work function of graphene by gate voltage: a method to increase hydrogen reactivity
Ning Shen and Jorge O. Sofo,
Department of Physics and Materials Research Institute, Penn State
In a study recently published in ACS Nano we have demonstrated that we can change the work function of graphene by more than one electron-volt with the use of a gate voltage. This control of the work function enables the tuning of the reaction barrier through an adjustment of the charge transfer. We found that when graphene is deposited on a silicon wafer becomes negatively charged. This charge transfer was confirmed experimentally by the group of Peter Eklund who is a coauthor in the publication mentioned before. Our density functional calculations show that the layer of SiO2 that naturally forms on the Si wafer has filled surface states close to the conduction band edge. These surface states lower the work function of the oxide to the level of facilitating charge transfer to the graphene sheet. We found that charge densities of the order of 1013 e/cm2 are easily obtained with moderate gate voltages. Associated with these charge transfer there is a shift in the chemical potential of the graphene sheet of the order of 1 eV and as a consequence we find a corresponding change in the work function. We expect that the change in the work function produced by the gate voltage will affect the reaction barrier for the adsorption and dissociation of molecular hydrogen ion the surface. Our preliminary results show that this is the case. The extra charge and the change in work function facilitate the reaction and the formation of graphane.