First-principles study of edge-modified armchair graphene nanoribbons

We have used first-principles methods to study the geometries and electronic structures of hydrogen (H), fluorine (F), chlorine (Cl), and hydroxyl (OH) terminated armchair graphene nanoribbons (H-AGNRs, F-AGNRs, Cl-AGNRs, and OH-AGNRs) with ribbon widths N = 7 and 19. The most stable geometries of H-AGNRs have planar configurations, but those of F-, Cl-, and OH-AGNRs have rippled edges. The ripples stem from steric hindrances between neighboring pairs of terminal atoms or groups, and the ripples are strongly localized to the edges. The most stable termination occurs with F atoms owing to strong C-F bonds despite their rippled edge structures. The energy band gaps of F- and Cl-AGNRs are narrower than those of H-AGNRs. This is due to structural deformations rather than chemical effects. For OH-AGNRs, chemical interactions between neighboring OH groups further reduce the band gaps.