Optical absorption of atomic-precise graphene nanoribbons on insulating substrate

We report the reflection contrast spectra of atomic-precise armchair graphene nanoribbons (GNRs) on insulating substrates. As-grown GNRs are transferred from gold to an insulating substrate by the “bubbling” method. Polarization control of light is employed to directly probe the one-dimensional (1D) optical resonances of armchair GNRs with different ribbon widths by the reflection contrast spectroscopy. We observed well-defined 1D optical resonances which are identified as optically-bright inter-band transitions in GNR samples. Our experimental interpretations are further supported by theoretical calculations within the GW framework, which reveals a strong excitonic effect with exceptionally large exciton binding energies.