Lightwave-driven scanning tunnelling spectroscopy of atomically precise graphene nanoribbons

R. Fasel,N. Everett,V. Jelic,P. Ruffieux,V. N. Breslin,Q. Sun,M. Hassan,T. L. Cocker,S. E. Ammerman,Y. Wei,S. Lee,C. A. Pignedoli

doi:10.1038/s41467-021-26656-3

Abstract

Atomically precise electronics operating at optical frequencies require tools that can characterize them on their intrinsic length and time scales to guide device design. Lightwave-driven scanning tunnelling microscopy is a promising technique towards this purpose. It achieves simultaneous sub-ångström and sub-picosecond spatio-temporal resolution through ultrafast coherent control by single-cycle field transients that are coupled to the scanning probe tip from free space. Here, we utilize lightwave-driven terahertz scanning tunnelling microscopy and spectroscopy to investigate atomically precise seven-atom-wide armchair graphene nanoribbons on a gold surface at ultralow tip heights, unveiling highly localized wavefunctions that are inaccessible by conventional scanning tunnelling microscopy. Tomographic imaging of their electron densities reveals vertical decays that depend sensitively on wavefunction and lateral position. Lightwave-driven scanning tunnelling spectroscopy on the ångström scale paves the way for ultrafast measurements of wavefunction dynamics in atomically precise nanostructures and future optoelectronic devices based on locally tailored electronic properties.

Highlights

Precise electronics operating at optical frequencies require tools that can characterize them on their intrinsic length and time scales to guide device design
We introduce lightwave-driven scanning tunnelling tomography, where constant-height THz-scanning tunnelling microscopy (STM) images illustrate a transition from tunnelling dominated by occupied states in the GNR valence bands to tunnelling dominated by unoccupied states in the GNR conduction bands within a tip-sample distance increase of just 1 Å
Conventional STS is performed by disengaging the feedback loop, applying an additional sinusoidal voltage of perturbative amplitude dV and detecting the sinusoidal current amplitude dI as a function of Vd.c. (Fig. 1b). This yields the slope of the current–voltage characteristic, which is approximately proportional to the energy-dependent local density of electronic states (LDOS) of the sample

Summary

Introduction

Precise electronics operating at optical frequencies require tools that can characterize them on their intrinsic length and time scales to guide device design. We utilize lightwave-driven terahertz scanning tunnelling microscopy and spectroscopy to investigate atomically precise seven-atom-wide armchair graphene nanoribbons on a gold surface at ultralow tip heights, unveiling highly localized wavefunctions that are inaccessible by conventional scanning tunnelling microscopy. Tomographic imaging of their electron densities reveals vertical decays that depend sensitively on wavefunction and lateral position. We investigate the promising material platform of atomically precise graphene nanoribbons[22] (GNRs) on the ångström scale with lightwave-driven terahertz scanning tunnelling microscopy (THz-STM) and spectroscopy (THz-STS). We introduce lightwave-driven scanning tunnelling tomography, where constant-height THz-STM images illustrate a transition from tunnelling dominated by occupied states in the GNR valence bands to tunnelling dominated by unoccupied states in the GNR conduction bands within a tip-sample distance increase of just 1 Å

Methods

Results

Conclusion