Tip-enhanced Raman scattering of graphene

This article reviews the mechanism of tip-enhanced Raman spectroscopy (TERS) and its importance for characterizing graphene. The theoretical foundation of TERS and experimental implementation are discussed. Conventionally, Raman scattering is treated as a spatially incoherent process where the total signal is proportional to the scattering volume. However, in the near-field regime, the scattered fields can add coherently because the TERS interaction volume is on the same length scale as the phonon correlation length. These coherence effects are significant for two-dimensional materials as will be discussed theoretically and experimentally. Therefore, TERS provides an optical method to probe phonon correlations at the nanoscale. In addition, this article will review the TERS applications for characterizing defects, edges, and nanoscale strain in graphene. Finally, the outlook and future applications are discussed