Scanning Raman Spectroscopy Of Nanostructured Graphene: Doping Due To Presence Of Edges

We report about scanning Raman experiments on, both, as deposited and nano-structured graphene flakes. The Raman scans allow us to extract spatially resolved information about frequencies, intensities and linewidths of the observed phonon modes. In nano-structured single-layer flakes, where periodic arrays of holes (antidots) were fabricated by electron-beam lithography and subsequent etching, we find a systematic dependence of the phonon frequencies, intensities and linewidths on the periods and hole sizes of the nano-patterned regions. A systematic shift of the G mode frequency evidences a doping effect in the nano-patterned regions. In order to calibrate the doping dependence of the G mode phonon frequency, we have investigated the position and linewidth of this mode in a gated single-layer flake. With this calibration, we can quantitatively determine the doping level, which is introduced via preparation of the periodic hole arrays into the samples. A comparison of G and 2D mode frequencies allows us to identify the doping to be of p-type.