Electronic Properties of Substitutionally Boron-doped Graphene Nanoribbons on a Au(111) Surface

TL;DR

This study investigates how substitutional boron doping affects the electronic properties of graphene nanoribbons on a gold surface, revealing impurity states and band structure modifications through combined experimental and theoretical methods.

Contribution

It provides new insights into the electronic effects of di-boron substitution in GNRs and how their band structure can be tuned by doping configuration.

Findings

Two boron-rich impurity bands appear inside the GNR band gap.

Boron doping shifts the conduction and valence bands away from the gap edge.

Hybridization with gold surface states broadens one of the impurity bands.

Abstract

High quality graphene nanoribbons (GNRs) grown by on-surface synthesis strategies with atomic precision can be controllably doped by inserting heteroatoms or chemical groups in the molecular precursors. Here, we study the electronic structure of armchair GNRs substitutionally doped with di-boron moieties at the center, through a combination of scanning tunneling spectroscopy, angle-resolved photoemission, and density functional theory simulations. Boron atoms appear with a small displacement towards the surface signaling their stronger interaction with the metal. We find two boron-rich flat bands emerging as impurity states inside the GNR band gap, one of them particularly broadened after its hybridization with the gold surface states. In addition, the boron atoms shift the conduction and valence bands of the pristine GNR away from the gap edge, and leave unaffected the bands above and below, which become the new frontier bands and have negligible boron character. This is due to the selective mixing of boron states with GNR bands according to their symmetry. Our results depict that the GNRs band structure can be tuned by modifying the separation between di-boron moieties.