Polarized Nonresonant Raman Spectra of Graphene Nanoribbons

We study the non-resonant Raman scattering of armchair- and zigzag-edged graphene nanoribbons using density functional perturbation theory. We find that in both types of nanoribbon, the Raman spectrum is extremely polarized along the ribbon length direction, over 102 times larger than those of the other orientations. Also we discover that the scattering intensity of this major polarization exhibits conspicuous quantum oscillation with the ribbon width in armchair-edged nanoribbons. While in zigzag-edged nanoribbons, the Raman spectra shows relatively weak dependence on the ribbon width. We propose employing the surface-enhanced Raman spectroscopy to detect these features, a procedure which has been applied in the studies of graphene.