Extreme electrochemical doping of a graphene–polyelectrolyte heterostructure
A doped state of heterostructure, based on chemical vapour deposition grown graphene and polyelectrolytes (polyallylamine hydrochloride and polyacrylic acid), has been studied. The doping was realized electrochemically by application of an electrode potential in LiClO4–acetonitrile electrolyte solution. Our new setup allowed us to achieve extreme doping levels for both positive and negative electrode potentials. The extreme doping of graphene was demonstrated by a large shift of the G mode frequency in the Raman spectrum. In addition a significant enhancement of the G mode at large positive and also negative electrode potentials has been experimentally observed. The G mode intensity enhancement was attributed to cancelling of a part of the quantum Raman pathways thus reducing the destructive quantum interference effect. Since this effect only occurs if the Fermi level achieves half of the laser excitation energy, experimental observation of this phenomenon also confirms the extreme doping levels of graphene.