Switching from Reactant to Substrate Engineering in the Selective Synthesis of Graphene Nanoribbons

Abstract

The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in predefined ways through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to date through top-down methods, is preserved by the self-assembly process. This new strategy's proof-of-concept compares experiments using 4,4''-dibromo-para-terphenyl as a molecular precursor on flat Au(111) and stepped Au(322) substrates. As opposed to the former, the periodic steps of the latter drive the selective synthesis of 6 atom-wide armchair GNRs, whose electronic properties have been further characterized in detail by scanning tunneling spectroscopy, angle resolved photoemission, and density functional theory calculations.

On‐Surface Synthesis of 8‐ and 10‐Armchair Graphene Nanoribbons

“…Pre‐synthesized poly‐ para ‐phenylene (3‐AGNRs) can laterally fuse with 5‐ and 7‐AGNRs to form desired products on Au (111) surface. In addition to 8‐ and 10‐AGNRs, other unknown AGNRs, for example, 11‐AGNRs, are ready to be prepared by lateral fusion between 5‐ and 6‐AGNRs with the help of stepped Au (322) surface . STS spectra together with 2D d I /d V mappings reveal for the first time the apparent band gap of 10‐AGNRs (2.0 ± 0.1 eV) and 8‐AGNRs (2.3 ± 0.1 eV) under similar measuring conditions.…”

On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors

“…We thus associate these two effects to Br-driven interactions, in line with previous reports of other brominated precursors on noble metal surfaces. 19 …”

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

“…However, to date, nonsymmetrical AGNRs can be only fabricated by extramolecular cyclodehydrogenation. For example, 6 and 12‐ AGNR are synthesized by the lateral fusion of molecule 2, whose band gaps are 1,69 eV, and 1.13 eV . 8‐ AGNR(V gap =2.3 eV), 10‐ AGNR (V gap =2.0 eV), 14‐ AGNR (see Figure k, V gap =0.2 eV) and 18‐ AGNR(V gap =0.9 eV) are likewise produced by the lateral fusion of molecule 1, molecule 2, molecule 3 and molecule 4, mutually.…”