Posted in | News | Microscopy

Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons

A team of researchers at Michigan State University have utilized lightwave-driven terahertz scanning tunneling microscopy and spectroscopy to probe 7-atom-wide armchair graphene nanoribbons (7-AGNRs) at ultralow heights. They have uncovered highly localized wave functions in GNR edges that conventional scanning tunneling microscopes have not revealed.

Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons.

Image Credit: Rost9/

Designing advanced optoelectronic devices requires the development of diagnostic tools operating at nanometer scales. Terahertz radiation is becoming an important tool in the development of new technologies.

To achieve nanoscale resolutions, terahertz scanning probe microscopes couple terahertz radiation to subwavelength-sized probes. This opens up new possibilities for the precise characterization of wavefunction dynamics in nanostructures and bodes well for future optoelectronic devices tailored through the modulation of local electronic properties.

A Quick Primer on Scanning Probe Microscopy

Ever since the scanning tunneling microscope was invented by two IBM researchers in 1981, scanning probe microscopes have underpinned innovations in materials science by revealing the morphology, topography and composition of structures at nanometer scales.

The many types of scanning probe microscopes include scanning tunneling microscopes, atomic force microscopes, and scanning electrochemical microscopes. They reveal far greater details than conventional optical microscopes because they use electron waves instead of light waves to “see” into objects. Since electron wavelengths are hundreds of thousands of times smaller than optical wavelengths, electron microscopes can resolve objects hundreds of thousands of times smaller than optical microscopes.

In scanning electron microscopes, a microscopic probe scans a sample with an electron beam so that the scattered electrons can be analyzed to form an image.

The study of graphene nanoribbons (GNRs) is essential to the development of novel nanoelectronic devices. Graphene nanoribbons are strips of graphene less than 100 nm wide. Graphene is one of the many allotropes of carbon - diamond and graphite are two other well-known allotropes of carbon.

At nanoscales, electronic confinement effects and edge structures govern the properties of graphene. In the zigzag edge structures of GNRs, each edge segment is at the opposite angle to the previous. In armchair edge structures, each pair of segments is at a 120-degree rotation angle to the prior pair. Armchair edge structures are either metallic or semiconducting. Zigzag edge structures are always metallic.

Lightwave-driven scanning tunneling microscopy (STM) opens up a new dimension of atomically resolved microscopy. Lightwave-control of extreme tunnel currents (and other fields) engenders ultrafast fields which can operate in regimes inaccessible to conventional static STM fields.

Lightwave-Driven Scanning Tunneling Microscopy

The team at Michigan State University, supported by the Swiss Federal Laboratories for Materials Science and Technology and the University of Bern, grew graphene nanoribbons from molecular precursors on a clean gold (Au) substrate using on-surface synthesis. They selected 7-atom-wide GNRs with armchair edges (7-AGNRs) for their study.

The team showed that the differential conductance on the gold surface substrate was highly sensitive to the lateral movement of the microscope’s nanoprobe. Thus, producing differential conductance maps by combining scanning tunneling microscopy (STM) and spectroscopy (STS) reveals a sample’s local density of electronic states (LDOS) as a function of position and energy.

Terahertz spectroscopy (THz-STS) was performed as a function of three-dimensional positioning above the GNRs. It allowed the team to extract the differential conductance sampled by lightwave-driven tunneling microscopy with ångström (10-10 meters) horizontal and sub-ångström vertical resolution. They also introduced lightwave-driven scanning tunneling tomography, where constant-height THz-STM images showed a transition from tunneling dominated by occupied states in the GNR valence bands to tunneling dominated by unoccupied states in the conduction bands.

The team applied spatially dependent THz-STS to disentangle the intrinsic properties of the 7-AGNR at ultralow probe tip heights from the lightwave-driven tunneling process. They defined ultralow tip heights as distances at which orbitally selective imaging by conventional STM with an s-wave tip becomes unfeasible because the DC current would either damage the tip or the sample.

Energetic positions and widths were constrained by fits to the spectroscopy data. Ultrafast photoemission sampling to detect the profile of the terahertz pulse at the tip of the probe was used. Combining this with the differential conductance data was sufficient to reproduce an image at a given probe position.

Lightwave-driven (terahertz) scanning tunneling microscopy, spectroscopy and tomography of GNRs open up new opportunities for the nanoscale engineering of novel materials.

References and Further Reading

Ammerman, S.E., et al., (2021) Lightwave-driven scanning tunnelling spectroscopy of atomically precise graphene nanoribbons. Nature Communications, [online] Available at:

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

William Alldred

Written by

William Alldred

William Alldred is a freelance B2B writer with a bachelor’s degree in Physics from Imperial College, London. William is a firm believer in the power of science and technology to transform society. He’s committed to distilling complex ideas into compelling narratives. Williams’s interests include Particle & Quantum Physics, Quantum Computing, Blockchain Computing, Digital Transformation and Fintech.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Alldred, William. (2021, November 25). Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons. AZoNano. Retrieved on February 28, 2024 from

  • MLA

    Alldred, William. "Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons". AZoNano. 28 February 2024. <>.

  • Chicago

    Alldred, William. "Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons". AZoNano. (accessed February 28, 2024).

  • Harvard

    Alldred, William. 2021. Lightwave-Driven Electron Microscope Probes Atom-Sized Graphene Nanoribbons. AZoNano, viewed 28 February 2024,

Tell Us What You Think

Do you have a review, update or anything you would like to add to this news story?

Leave your feedback
Your comment type
Azthena logo powered by Azthena AI

Your AI Assistant finding answers from trusted AZoM content

Your AI Powered Scientific Assistant

Hi, I'm Azthena, you can trust me to find commercial scientific answers from

A few things you need to know before we start. Please read and accept to continue.

  • Use of “Azthena” is subject to the terms and conditions of use as set out by OpenAI.
  • Content provided on any AZoNetwork sites are subject to the site Terms & Conditions and Privacy Policy.
  • Large Language Models can make mistakes. Consider checking important information.

Great. Ask your question.

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.