Signature Vibrational Bands for Defects in CVD Single-Layer Graphene by Surface-Enhanced Raman Spectroscopy

We report the observation of signature vibrational bands in the frequency region between 900 and 1600 cm(-1) for defects in single-layer graphene (SLG) using surface Raman spectroscopy in ultrahigh vacuum. Vapor deposition of Ag leads to the formation of surface nanoparticles that migrate to defects in the SLG, leading to surface-enhanced Raman scattering (SERS) of the graphene G and 2D bands as well as new vibrational modes ascribed to native defects. Many of the new spectral bands of these native defects are similar, although not identical, to those predicted previously for -C2 defects. These new bands are observed in addition to bands more commonly observed for defective graphene that are attributed to the D, G*, D+G, and 2D' modes. The defects observed in these SLG films are not believed to result from the Ag deposition process but are postulated to be formed during the graphene CVD growth process. These defects are then made visible by postdeposition of Ag due to SERS.