Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy

TL;DR

This study uses Fourier-transformed scanning tunneling spectroscopy combined with theoretical calculations to directly measure the electronic band dispersion, effective masses, and band gap of atomically precise armchair graphene nanoribbons.

Contribution

It introduces a method to extract the electronic dispersion relations of graphene nanoribbons directly from STS data, supported by density functional theory calculations.

Findings

Determined the band gap of 7-AGNRs as 2.37 eV.

Measured effective masses for valence, conduction, and next empty bands.

Mapped the energy-dependent standing wave patterns to extract dispersion relations.

Abstract

Atomically precise armchair graphene nanoribbons of width $N=7$ (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis of energy-dependent standing wave patterns of finite length ribbons allows, by Fourier transformation, the direct extraction of the dispersion relation of frontier electronic states. Aided by density functional theory calculations, we assign the states to the valence band, the conduction band and the next empty band of 7-AGNRs, determine effective masses of $0.42\pm 0.08\,m_e$, $0.40\pm 0.18\,m_e$ and $0.20\pm 0.03\,m_e$, respectively, and a band gap of $2.37\pm 0.06$ eV.