Direct experimental determination of onset of electron-electron interactions in gap opening of zigzag graphene nanoribbons

Abstract

Nanoribbons are model systems for studying nanoscale effects in graphene. For ribbons with zigzag edges, tunable bandgaps have been predicted due to coupling of spin-polarized edge states, which have yet to be systematically demonstrated experimentally. Here we synthesize zigzag nanoribbons using Fe nanoparticle-assisted hydrogen etching of epitaxial graphene/SiC(0001) in ultrahigh vacuum. We observe two gaps in their local density of states by scanning tunnelling spectroscopy. For ribbons wider than 3nm, gaps up to 0.39eV are found independent of width, consistent with standard density functional theory calculations. Ribbons narrower than 3nm, however, exhibit much larger gaps that scale inversely with width, supporting quasiparticle corrections to the calculated gap. These results provide direct experimental confirmation of electron-electron interactions in gap opening in zigzag nanoribbons, and reveal a critical width of 3nm for its onset. Our findings demonstrate that practical tunable bandgaps can be realized experimentally in zigzag nanoribbons. © 2014 Macmillan Publishers Limited.