Atomic Scale Visualization of Vibrational Modes in Armchair Graphene Nanoribbon

Using scanning tunneling microscopy (STM) and inelastic tunneling spectroscopy, the low‐frequency vibrational modes of a 7‐atom wide armchair graphene nanoribbon (7‐AGNR) is mapped. The inelastic tunneling channel is enhanced over the elastic one by a covalently bonded 7‐AGNR to the apex of an STM tip. This setup has led to resonant inelastic tunneling between vibrational states of supported 7‐GNR on Au(111) substrate and the states of the functionalized STM tip. The low‐energy spectra reveal two localized peaks at the armchair edges with energies at ±14 and ±30 mV. The peaks are assigned to twice the energies of longitudinal compressive and shear‐like modes of 7‐AGNR, respectively. Remarkably, the well‐separated peaks evolve rapidly into one broader peak toward the bulk of the ribbon due to scattering from substrate interactions. This suggests that edge state phonons are uniquely protected from the microenvironment and may have a profound effect on the transport properties of GNR devices.