A collaborative team of Graphene Flagship partners from DTU, Denmark, IIT, Italy, Aalto University, Finland, AIXTRON, UK, imec, Belgium, Graphenea, Spain, Warsaw University, Poland, and Thales R&T, France, as well as collaborators in China, Korea and the US, has come together to develop and mature terahertz spectroscopy techniques, that can penetrate graphene films and enable the creation of detailed maps of their electrical quality, without damaging or contaminating the material. The result of this collaborating is a novel measurement tool for graphene characterization.

Graphene is often ‘sandwiched’ between many different layers and materials to be used in electronic and photonic devices, which complicates the process of quality assessment. Terahertz spectroscopy can help by imaging the encapsulated materials and revealing the quality of the graphene underneath, exposing imperfections at critical points in the fabrication process. It is a fast, non-destructive technology that probes the electrical properties of graphene and layered materials, with no need for direct contact.

The development of characterization techniques like terahertz spectroscopy is fundamental to accelerating large-scale production, as they guarantee that graphene-enabled devices are made consistently and predictably, without detrimental flaws.

“This is the technique we needed to match the high-throughput production levels enabled by the Graphene Flagship,” explains Peter Bøggild from DTU. “We are confident that terahertz spectroscopy in graphene manufacturing will become as routine as X-ray scans in hospitals,” he adds. “In fact, thanks to terahertz spectroscopy you can easily map even meter-scale graphene samples without touching them, which is not possible with some other state-of-the-art techniques.” Furthermore, the Graphene Flagship is currently studying how to apply terahertz spectroscopy directly into roll-to-roll graphene production lines, and speed up the imaging.

The newly developed method for terahertz spectroscopy is on track to become a standard technical specification, thanks to the work of the Graphene Flagship Standardization Committee.

“This will undoubtedly accelerate the uptake of this new technology, as it will outline how analysis and comparison of graphene samples can be done in a reproducible way,” explains Peter Jepsen from DTU, who co-authors the study. “Terahertz spectroscopy is yet another step to increase the trust in graphene-enabled products,” he concludes.

Amaia Zurutuza, co-author of the paper and Scientific Director at Graphenea, says: “At Graphenea, we are convinced that terahertz imaging can enable the development of quality control techniques capable of matching manufacturing throughput requirements and providing relevant graphene quality information, which is essential in our path towards the successful industrialization of graphene.”