Resonance Raman Spectroscopy of 7-Atom Wide Armchair Graphene Nanoribbons*

Graphene Nanoribbons (GNRs) exhibit interesting electronic and optical properties strongly dependent on their width and edge.The bottom-up approach to fabricate graphene nanoribbons leads to a precise width and extremely high edge quality, and, as a consequence of this uniformity, the quantum confinement plays a significant role in its electronic and optical properties. This work reports the optical response of armchair graphene nanoribbons of width N=7 atom (7AGNR) on Si/SiO2 substrate using Raman spectroscopy. The 7AGNR presents a rich Raman spectrum, with more than 20 peaks, in good agreement with the theoretical predictions. At room temperature, the nanoribbons degrade in a few seconds under laser exposition as shown by time series Raman experiments. Under nitrogen atmosphere and low temperature, the degradation process is shown to be much slower, allowing us to perform resonance Raman spectroscopy of the 7AGNR in a wide range of excitation energies. The results show a strong dependence of the Raman spectrum with the excitation energy, with a resonance peak around 2.3 eV in agreement with reflectance experiments.