Electronic structure changes during the on-surface synthesis of nitrogen-doped chevron-shaped graphene nanoribbons

• Published in: Physical review. B 2017-07, Vol.96 (4), Article 045434
• Main Authors: Maaß, Friedrich, Utecht, Manuel, Stremlau, Stephan, Gille, Marie, Schwarz, Jutta, Hecht, Stefan, Klamroth, Tillmann, Tegeder, Petra
• Format: Article
• Language: English
• Subjects: Band gap; Chemical synthesis; Density functional theory; Electron energy loss spectroscopy; Electronic properties; Electronic structure; Elongation; Energy dissipation; Energy gap; Graphene; Nanoribbons; Nitrogen; Precursors
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.96.045434

Utilizing suitable precursor molecules, a thermally activated and surface-assisted synthesis results in the formation of defect-free graphene nanoribbons (GNRs), which exhibit electronic properties that are not present in extended graphene. Most importantly, they have a band gap in the order of a few electron volts, depending on the nanoribbon width. In this study, we investigate the electronic structure changes during the formation of GNRs, nitrogen-doped (singly and doubly N-doped) as well as non-N-doped chevron-shaped CGNRs on Au(111). Thus we determine the optical gaps of the precursor molecules, the intermediate nonaromatic polymers, and finally the aromatic GNRs, using high-resolution electron energy loss spectroscopy and density functional theory calculations. As expected, we find no influence of N-doping on the size of the optical gaps. The gap of the precursor molecules is around 4.5 eV. Polymerization leads to a reduction of the gap to a value of 3.2 eV due to elongation and thus enhanced delocalization. The CGNRs exhibit a band gap of 2.8 eV, thus the gap is further reduced in the nanoribbons, since they exhibit an extended delocalized π-electron system.