Linear tuning of charge carriers in graphene by organic molecules and charge-transfer complexes

The electronic interactions of several organic donor/acceptor molecules or combination of these molecules (hereafter known as ``charge-transfer complexes'') with graphene have been investigated by first-principles calculations and photoemission spectroscopy experiments. It is found that the doping behavior of graphene can be controlled by the ratio of donor and acceptor molecules in the form of their charge-transfer complexes. The interfacial electronic structure of molecules adsorbed on graphene is dominated by the charge-transfer mechanism. The changes in work function of graphene modified by organic molecules are discussed in comparison with experiments and they are in good agreement with experimental data. Our results show that functionalization of graphene by acceptor/donor molecules and their charge-transfer complexes is an efficient way to control the doping behavior of graphene.