Edge Doping Effect to the Surface Plasmon Resonances in Graphene Nanoribbons

In this work, we investigated the edge doping effect to graphene plasmon resonances in graphene nanoribbons (GNRs), which is known to affect the electronic doping of GNRs but has not been systematically studied. We found the Fermi levels, which reflect that the sheet charge carrier densities, extracted from the graphene plasmon resonance frequencies, vary across GNRs of different widths on the same sample. Using Raman spectroscopy, we confirmed that the variation of the sheet charge carrier density is caused by edge doping, which has a stronger effect on narrower GNRs. To further understand the edge doping effect, electron beam irradiation (EBI) is applied to modify the charge state of the edge. Using EBI, we successfully demonstrated the tuning of the graphene plasmon resonances due to the change of the edge doping states. These findings demonstrated the importance of the edge doping effect in determination of the surface plasmon frequency in GNRs.