Linkage Between Micro- and Nano-Raman Spectroscopy of Defects in Graphene

On nanomaterials characterization, the evolution from the broadly utilized micro-Raman spectroscopy to a nanoscale regime is taking place with the improvements in tip-enhanced Raman spectroscopy (TERS). It is not clear, however, to which extent protocols developed within the diffraction-limited far-field configuration apply to the near-field regime. Defects in graphene nanoflakes are investigated in this work in both micro and nano regimes, showing that the Raman characteristics utilized to quantify defects in the far-field regime actually change in the presence of the TERS tip, generating incompatible results. The micro-to-nano spectral mismatch can be modeled using a theory of spatial coherence in near-field Raman scattering, from which a parameterization procedure can be derived in order to obtain consistent results. The incompatibilities observed here for graphene should also happen in other structures relevant to nanoscience and nanotechnology when explored in the nano-Raman regime, and they can be resolved similarly.