On-Surface Synthesis of NBN-Doped Zigzag-Edged Graphene Nanoribbons.

Yubin Fu,Hong‐Jun Gao,Junzhi Liu,Huan Yang,Zhihai Cheng,Hongliang Lu,Xinliang Feng,Yixuan Gao,Reinhard Berger,Shixuan Du,Li Huang

doi:10.1002/anie.202000488

Abstract

We report the first bottom‐up synthesis of NBN‐doped zigzag‐edged GNRs (NBN‐ZGNR1 and NBN‐ZGNR2) through surface‐assisted polymerization and cyclodehydrogenation based on two U‐shaped molecular precursors with an NBN unit preinstalled at the zigzag edge. The resultant zigzag‐edge topologies of GNRs are elucidated by high‐resolution scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc‐AFM). Scanning tunneling spectroscopy (STS) measurements and density functional theory (DFT) calculations reveal that the electronic structures of NBN‐ZGNR1 and NBN‐ZGNR2 are significantly different from those of their corresponding pristine fully‐carbon‐based ZGNRs. Additionally, DFT calculations predict that the electronic structures of NBN‐ZGNRs can be further tailored to be gapless and metallic through one‐electron oxidation of each NBN unit into the corresponding radical cations. This work reported herein provides a feasible strategy for the synthesis of GNRs with stable zigzag edges yet tunable electronic properties.

Highlights

We report the first bottom-up synthesis of NBNdoped zigzag-edged graphene nanoribbons (GNRs) (NBN-ZGNR1 and NBNZGNR2) through surface-assisted polymerization and cyclodehydrogenation based on two U-shaped molecular precursors with an NBN unit preinstalled at the zigzag edge
These edge topologies include armchair, chevron, cove, and zigzag.[1a,4] Compared to armchair-edged or cove-edged GNRs (AGNRs or CGNRs), zigzag-edged GNRs (ZGNRs) are predicted to preserve gapless or metallic band structures[5] as well as host spinpolarized electronic edge states, which render them promising materials in spintronics.[4b,6] these fascinating properties have barely been observed experimentally due to the lack of a facile synthetic approach and the poor stability of the ZGNRs.[7]
Scanning tunneling spectroscopy (STS) measurements demonstrated the existence of localized edge states with a large energy splitting at the zigzag edges.[4b]. On the other hand, partial ZGNRs have raised substantial interest since they can enhance the stability and tune their electronic and magnetic properties, and among them, the most prominent examples exhibit quasi-one-dimensional trivial and nontrivial electronic quantum phases.[3c,8] heteroatom doping, such as the incorporation of boron and oxygen/nitrogen atoms, at the edges or the central sp2-carbon frameworks of GNRs has been recently demonstrated to modulate the conductance and valence bands of the ribbons and provide access to stable ZGNRs.[9]

Summary

Introduction

We report the first bottom-up synthesis of NBNdoped zigzag-edged GNRs (NBN-ZGNR1 and NBNZGNR2) through surface-assisted polymerization and cyclodehydrogenation based on two U-shaped molecular precursors with an NBN unit preinstalled at the zigzag edge.

Results

Conclusion