Polarized Vibrational Infrared Absorption of Graphene Nanoribbons

We present for the first time the linearly polarized vibrational infrared spectra of edge-hydrogenated armchair and zigzag graphene nanoribbons (GNRs) through first-principles calculations. We find that there exists a prominent and width-insensitive peak in both GNRs for out-of-plane polarization, which can be used as a benchmark in measurements. In the major absorption regions of all polarizations, we observe noticeable differences between the two GNR types. In armchair GNRs, the spectra for in-plane polarization oscillate with the ribbon width, while in zigzag GNRs the dispersion relationship bears close resemblance with that of graphene. We also discover a special peak that reflects the mirror symmetry between the two edges of zigzag GNRs. Finally, the quenching of magnetism and oxygen-passivation are revealed to remarkably influence the infrared spectra. Our work provides a new insight into GNR fundamental property and is expected to help confront the current problem of edge structure and magnetism identification of GNRs.