Band Gap of Atomically Precise Graphene Nanoribbons as a Function of Ribbon Length and Termination

TL;DR

This study investigates how the band gap of atomically precise 7-AGNRs varies with length and termination, revealing convergence to bulk values and the influence of termination chemistry.

Contribution

It provides detailed insights into the dependence of the band gap on ribbon length and termination, combining experimental STM/STS data with DFT calculations.

Findings

Band gap converges to 2.3 eV for ribbons longer than 6 nm

Short ribbons exhibit significantly larger band gaps

Termination chemistry significantly affects the band gap

Abstract

We study the band gap of finite $N_A=7$ armchair graphene nanoribbons (7-AGNRs) on Au(111) through scanning tunneling microscopy/spectroscopy combined with density functional theory calculations. The band gap of 7-AGNRs with lengths of 6 nm and more is converged to within 0.1 eV of its bulk value of 2.3 eV, while the band gap opens by several hundred meV in very short 7-AGNRs. The termination has a significant effect on the band gap, doubly hydrogenated termini yielding a lower band gap than singly hydrogenated ones.