Electronic structures of defects in bottom-up N-doped graphene nanoribbons: Experiment and theory

Abstract

Graphene nanoribbons (GNRs) possess atomically tunable electronic structures via modulating the width, edge structures and various defects. Here, the electronic structures of three experimentally observed defects (substitutional site defect Ds, vacancy defect Dv and pentagon topological defect Dp) in N-9-AGNRs on the Au(111) substrate are systematically investigated. Scanning tunneling spectroscopy (STS) analysis reveals that Ds induces a subversive variation which results in metallic character, while the Dv and Dp reduce the band gap from 1.75 eV to 1.34/1.02 eV respectively. Further first-principles calculations reveal that the N-9-AGNR(Ds), N-9-AGNR(Dv), and N-9-AGNR(Dp) possess electrostatic potential differences of 0.55, 0.21 and −0.24 eV respectively, which drives the separation of electrons and holes. With the defect concentration increasing, the band gaps initially reduce and then increase for both N-9-AGNR(Dv) and N-9-AGNR(Dp). Moreover, the optical absorbances of the pristine N-9-AGNR, N-9-AGNR(Dv), and N-9-AGNR(Dp) in the infrared spectral region are ∼6–8%, indicating that it is beneficial to be applied in infrared detectors, optoelectronic devices, biomedicine and other areas with high infrared radiation. Our findings can provide references for experimental researchers to extend the experimentally fabricated N-9-AGNRs in the future applications.