First-principles calculations of electrical conductivities of edge-modified graphene nanoribbons: Strain effect

Abstract

We investigate the influence of strain on the electrical properties of graphene nanoribbons that have potential applications in making sensors and other optoelectronic devices. In particular, we chose pristine armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH), boron doped armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH-B) and armchair graphene nanoribbons with 7 zigzag edges that have one carbon atom vacancy (7aGNRsH-V). Based on first-principles calculations, results show that pristine unstrained 7aGNRsH is electrically nonconductive but turns to be electrically conductive in a wide range of energy spectrum , e.g., from IR to visible to UV, due to the application of strain engineering. In metallic unstrained and strained 7aGNRsH-B and 7aGNRsH-V, non-vanishing electrical conductivity in the IR, visible and UV energy spectrum regimes are observed. We also investigate the influence of strain on the Berry curvature of 7aGNRsH, 7aGNRsH-B and 7aGNRsH-V nanoribbons. The results show that fermions are spread through out the Brillouin zone in the reciprocal space for semiconducting unstrained 7aGNRsH but localized near the Γ -point for strained 7aGNRsH that have out-of-plane deformations due to strain engineering. For metallics 7aGNRsH-B and 7aGNRsH-V, Berry curvature plots show that fermions are localized far away from the Γ -point. In two atom boron doped p-type armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH-2B), large peaks in electrical conductivity at IR energy spectrum regimes can be observed. These peaks of electrical conductivities in 7aGNRSH-2B may be detectable in experimentally synthesized structure in Cloke et al. (2015) [1] . • In Figs. 2 , 3 , 4 , we have provided results for band structures calculations obtained from pw.x and maximally localized wannier 90 method that are in excellent agreement. This provides foundation for investigation of influence of strain on the Berry curvature and electrical conductivity. Note that 7 boron doped armchair graphene nanoribbons in Fig. 3 and one carbon vacancy in 7 armchair graphene nanoribbons in Fig. 4 are metallic in nature. • When we apply strain, we have a relaxed shape armchair graphene nanoribbon and thus we expect localization of fermions near Gamma-point which can be clearly seen in Fig. 8 . • Since Fermi energy stays below the top of the valence band in metallic boron doped and vacancy of one carbon atom in graphene nanoribbon, we see the cut-off point in Berry curvature in Fig. 5 . • Most importantly in Figs. 6 , 11 and 12 , we see that intrinsic 7 armchair graphene nanoribbon is not conductive but metallic boron doped and vacancy created nanoribbon are conductive in the wide range of energy spectrum regimes, e.g., from IR to visible to UV.