Isotope-Labeled Graphene Reveals the Extrinsic Origin of Raman Signatures Assigned to Graphene Edge Modes

Sharp Raman bands near 1450 and 1530 cm –1 observed under 633 nm excitation have previously been attributed to localized vibrational modes of zigzag and armchair graphene edges. Here, we employ an isotope-resolved Raman spectroscopy approach to investigate the origin of these features. Monolayer 13 C graphene was synthesized and transferred alongside 12 C graphene reference samples, enabling a direct comparison of isotope-dependent Raman signatures under identical processing conditions. Despite clear isotope-induced shifts of the intrinsic graphene modes, the peaks near 1450 and 1530 cm –1 exhibit no isotope-dependent frequency shift, demonstrating that they do not originate from graphene lattice vibrations. Instead, their excitation-wavelength dependence and spectral characteristics are consistent with Raman enhancement of adsorbed molecular species under resonant conditions. These results establish isotope labeling as a robust experimental strategy for distinguishing intrinsic graphene vibrational modes from extrinsic Raman signals and provide a revised interpretation of Raman features previously attributed to graphene edge phonons.