Atomically precise nitrogen-doped graphene nanoribbons for electronics and data storage

We report the on-surface synthesis and spectroscopic characterization of several varieties of nitrogen-doped graphene nanoribbons (GNRs), which include straight N=9 armchair GNRs and chevron-family GNRs. The nanoribbons were synthesized on Au(111) substrates with atomic precision via on-surface coupling of specially designed molecular precursors. We demonstrate that the edge nitrogen atoms in these GNRs can be unambiguously identified using a variety of imaging techniques, such as scanning tunneling microscopy (STM), dI/dV mapping and noncontact atomic force microscopy combined with the image simulation using the mechanical probe particle method. Using scanning tunneling spectroscopy, we determined that the nitrogen-doped N=9 armchair GNRs have a bandgap of about 1.43 eV, which is very close to that of undoped GNRs. High-resolution dI/dV mapping enabled visualization of the local density of states (LDOS) at the valence band (VB) and conduction band (CB) energies. In accordance with the theoretical simulations, the highest LDOS at the VB energy was found at the more electronegative nitrogen atoms, while at the CB energy the dI/dV signal was higher for the unoccupied states on the edge carbon atoms. We experimentally verified theoretical predictions that the nitrogen doping of GNRs lowers the VB and CB energies but has no significant effect on the magnitude of the bandgap. The N-doped chevron GNRs were shown to be suitable for STM-controlled data storage.