On-Surface Synthesis of Armchair-Edged Graphene Nanoribbons with Zigzag Topology

Graphene nanoribbons (GNRs) are of enormous research interest as a promising active component in electronic devices, for example, field-effect transistors (FET). The recently developed "bottom-up" on-surface synthesis provides an unprecedented approach for the generation of GNRs on metal surfaces with atomic precision. In order to fabricate well-defined GNRs on surfaces, numerous previous works have been focused on the delicate engineering of building blocks. Lateral fusion of polyphenylene chains into GNRs, as a more flexible method, now has received an increasing attention. However, the lateral fusion into GNRs reported to date is merely limited to the straight GNRs. The GNRs with other topologies potentially displaying distinctive electronic properties are rarely reported. In this work, we report the synthesis of armchair-edged graphene nanoribbons (AGNRs) with zigzag topology for the first time via a stepwise polymerization reaction starting from 4,4 "-dibromo-m-terphenyl (DMTP) precursor on Au(111). Self-assembled unreacted monomers, covalent dimers, and zigzag polyphenylene chains are observed at different temperatures. Various GNRs with zigzag topology, including 6-AGNRs, 9-AGNRs, and nanoporous AGNRs are eventually produced through lateral fusion of polyphenylene chains. This study further diversifies the GNR family. Confining the zigzag polyphenylene chains in an ideal arrangement for subsequent lateral fusion can be explored in the future.