Infrared Absorption Spectra of Undoped and Doped Few-Layer Graphenes

The infrared absorption spectra of undoped few-layer graphenes with the layer number of N= 1-6, the hole- and electron-doped few-layer graphenes with the layer number of N= 1-4 have been studied based upon the tight-binding model. It is found that in contrast with the featureless optical spectrum of the undoped monolayer graphene, the undoped AB-stacking bi-, tri-, tetra- and more-layer graphene exhibit characteristic jumps in their infrared absorption (IR) spectra, which are caused by coupling between different layers. It is also found that the clear peaks exist in the IR spectra of the hole or electron-doped bi-, tri- and tetra-layer graphenes, which are induced by the strong IR transitions between their parallel valence or conduction bands. Based upon their different IR spectra, a powerful experimental tool has been proposed to identify accurately the layer number and doping type for the few-layer graphenes.