Nanospectroscopic Imaging of Defects of Chemical Vapor Deposition-Grown Graphene by Tip-Enhanced Raman Spectroscopy

The engineering of graphene defects could introduce novel functionalities, such as enhanced catalytic activity and unique electronic properties. However, their nanoscale characterization with chemical specificity remains challenging. Here, we employed tip-enhanced Raman spectroscopy (TERS) to achieve nanoscale visualization of defects, including edges and pleat folds, in chemical vapor deposition-grown graphene. TERS mapping of the D band identified the structures of graphene edges, potentially distinguishing armchair and zigzag configurations. Spectroscopic analysis revealed distinct features in pleat folds, with the 2D band exhibiting a blue shift compared to monolayer graphene, attributed to a reduced energy dispersion slope near the Dirac point and decreased Fermi velocity. Additionally, variations in the twisted angle of the middle layer of folds may induce the opposite shift of the 2D bandwidth and 2D/G intensity ratio. Leveraging the results obtained from ABA-stacking trilayer graphene with varying twisted angles, we are able to quantitatively determine the structures of graphene folds. This work provides a detailed spectroscopic understanding of graphene defects at the nanoscale, offering insights for defect engineering and the optimization of graphene’s functional properties for advanced applications.