Orbitally Matched Edge-Doping in Graphene Nanoribbons

Abstract

A series of trigonal planar N-, O-, and S-dopant atoms incorporated along the convex protrusion lining the edges of bottom-up synthesized chevron graphene nanoribbons (cGNRs) induce a characteristic shift in the energy of conduction and valence band edge states along with a significant reduction of the band gap of up to 0.3 eV per dopant atom per monomer. A combination of scanning probe spectroscopy and density functional theory calculations reveals that the direction and the magnitude of charge transfer between the dopant atoms and the cGNR backbone are dominated by inductive effects and follow the expected trend in electronegativity. The introduction of heteroatom dopants with trigonal planar geometry ensures an efficient overlap of a p-orbital lone-pair centered on the dopant atom with the extended π-system of the cGNR backbone effectively extending the conjugation length. Our work demonstrates a widely tunable method for band gap engineering of graphene nanostructures for advanced electronic applications.

Scanning Probe Microscopy of Topological Structure Induced Electronic States of Graphene

“…For a series of cGNRs synthesized on Au(111), N, O, and S atoms incorporated into the convex protrusion sites were identified by STM and AFM imaging due to the distinct electron densities of these heteroatom dopants (Figure 4i–k). A characteristic shift of valence and conduction band edges along with a reduction of band gaps were revealed by d I /d V spectra (Figure 4l). The spatially modulated electronic structure observed along the cGNR can be attributed to the interplay of a partial electron transfer between the dopants and GNRs backbone, and the effective conjugation arising from the overlap of the p‐orbital lone‐pairs of the dopant atoms with the extended π‐systems.…”

“…Spectra are offset vertically. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…O and S atoms could also be introduced in the carbon matrix as dopants. Differing from B and N atoms, O and S can only decorate the edge of GNR because they are dicovalent atoms . For a series of cGNRs synthesized on Au(111), N, O, and S atoms incorporated into the convex protrusion sites were identified by STM and AFM imaging due to the distinct electron densities of these heteroatom dopants (Figure 4i–k).…”

Tuning the Electronic Properties of Atomically Precise Graphene Nanoribbons by Bottom‐Up Fabrication

“…Besides heteroatom doped CGNRs mentioned above, O‐doped CGNRs, N‐doped CGNRs and S‐doped CGNRs (Figure d to 19i) also be synthesized by molecule 28. But their band gaps have a little change …”

“…(c) STM dI/dV point spectra obtained for a fluorenone GNR and an unfunctionalized chevron GNR on Au(111) substrate . (d, e), (f, g) and (h, i) STM topographic images and NC‐AFM image of O‐doped CGNRs, N‐doped CGNRs and S‐doped CGNRs, respectively . (j) corresponding STM dI/dV point spectra of O‐CGNR, N‐CGNR and S‐CGNR .…”