Length-Dependent Evolution of Type II Heterojunctions in Bottom-Up-Synthesized Graphene Nanoribbons

Abstract

The ability to tune the band-edge energies of bottom-up graphene nanoribbons (GNRs) via edge dopants creates new opportunities for designing tailor-made GNR heterojunctions and related nanoscale electronic devices. Here we report the local electronic characterization of type II GNR heterojunctions composed of two different nitrogen edge-doping configurations (carbazole and phenanthridine) that separately exhibit electron-donating and electron-withdrawing behavior. Atomically resolved structural characterization of phenanthridine/carbazole GNR heterojunctions was performed using bond-resolved scanning tunneling microscopy and noncontact atomic force microscopy. Scanning tunneling spectroscopy and first-principles calculations reveal that carbazole and phenanthridine dopant configurations induce opposite upward and downward orbital energy shifts owing to their different electron affinities. The magnitude of the energy offsets observed in carbazole/phenanthridine heterojunctions is dependent on the length of the GNR segments comprising each heterojunction with longer segments leading to larger heterojunction energy offsets. Using a new on-site energy analysis based on Wannier functions, we find that the origin of this behavior is a charge transfer process that reshapes the electrostatic potential profile over a long distance within the GNR heterojunction.

Graphene Nanoribbons: On‐Surface Synthesis and Integration into Electronic Devices

“…[ 91 ] Copyright 2018, Elsevier Ltd. f) Reproduced with permission. [ 112 ] Copyright 2019, American Chemical Society. g) Reproduced with permission.…”

“…Recently, these groups further designed a molecular building block bearing a 9‐methyl‐9 H ‐carbazole substituent (monomer 20 ) for GNR synthesis. [ 112,114 ] Remarkably, the carbazole substituent in the GNRs could undergo a secondary thermally induced transformation, which led to either a fused phenanthridine (characterized by a six‐membered ring) or a fused carbazole (characterized by a five‐membered ring) unit incorporated into the GNRs, resulting in a heterojunction with different segment lengths (Figure 6e,f). Owing to their different electron affinities, the carbazole and phenanthridine configurations exhibited electron‐donating and electron‐withdrawing behavior, respectively, inducing upward and downward orbital energy shifts.…”

Modified Engineering of Graphene Nanoribbons Prepared via On‐Surface Synthesis

“…b) Bond‐resolved STM (BRSTM) image of GNR heterojunction in (a). a,b) Reproduced with permission . Copyright 2019, American Chemical Society.…”

“…Edge postprocessing (such as edge reconstruction) and GNR fusion approaches were reported. Marangoni et al and Rizzo et al found edge reconstruction in the regions doped with N atoms may occur to form different segments ( Figure a,b). The irregular distribution of the rearrangement regions leads to the heterojunctions with random sequences.…”

Atomic‐Level and Modulated Interfaces of Photocatalyst Heterostructure Constructed by External Defect‐Induced Strategy: A Critical Review

“…Engineering photocatalyst heterostructures is one of the most practical and effective ways of developing photocatalysts for the spatial separation of electron–hole pairs, [ 20–22 ] which include conventional type‐II heterojunctions, [ 23–25 ] p–n heterojunctions, [ 26–28 ] and Z ‐scheme heterojunctions. [ 29–31 ] By applying a band matching principle, 0D, 1D, and 2D materials were selected for composite fabrication.…”