Tunable charge transfer

Nano Lett. http://doi.org/9pp (2015)

Credit: AMERICAN CHEMICAL SOCIETY

The electrical properties of graphene are highly sensitive to the perturbation of carrier concentration that is induced by the physisorption of molecules on its surface. Now, Manoharan Muruganathan and colleagues show that the van der Waals interactions between graphene and CO₂ molecules adsorbed onto it can be tuned by applying an external electric field. By means of first-principle calculations and transport measurements, they demonstrate that the molecules behave as weak electron acceptors when no voltage is applied to the substrate, and that such electron transfer increases under the effect of a positive voltage. In contrast, a negative voltage reverses the charge-transfer direction, causing the CO₂ molecules to behave as donors. This is because the external electric field alters the internal dipole created in the graphene–CO₂ complex together with the bonding distance and the O–C–O angle in the molecule. The researchers suggest that such effects may be useful for the realization of graphene-based gas sensors with improved molecule-recognition capabilities.