Local enhancement of inelastic tunnelling in epitaxial graphene on SiC(0001)

We have measured the elastic and inelastic tunnelling properties of epitaxial graphene on SiC(0001) using cryogenic scanning tunnelling spectroscopy. We find that the dominant inelastic channel of the out-of-plane acoustic graphene phonon at 70mV is spatially localized to particular regions of the graphene-SiC system that contain localized states. At these locations the maximum inelastic tunnelling channel reaches up to half of the total tunnelling current. The local enhancement of the inelastic tunnelling is found at the localized electron states of the graphene/SiC interface layer. Nonequilibrium Green's function formalism theory calculations indicate that this intense inelastic channel arises from graphene phonon modes strongly coupled to narrow electron states.