Terahertz Imaging of Graphene Paves the Way to Optimization, Industrialization

Researchers from Graphene Flagship have created a new measurement system for graphene and layered material analysis that could speed up production and optimize device fabrication.

X-rays have revolutionized medical treatment by allowing us access to the inside of patients without surgery. Terahertz spectroscopy can penetrate graphene films, allowing scientists to create detailed maps of the electrical quality without contaminating or damaging them. This analytical technique was developed and refined by researchers from industry and academia through the Graphene Flagship. Now, a new measurement tool is available for graphene characterization.

This effort was made possible by the collaborative environment created by the Graphene Flagship European Consortium, which included participation from scientists from DTU, Denmark, and IIT, Italy, as well as collaborators from China, Korea, and the US.

Graphene is often “sandwiched” between different layers and materials to be used as a component of electronic and photonic devices. This makes it difficult to assess quality. Terahertz spectroscopy simplifies things. It photographs the encapsulated materials and shows the quality of the graphene beneath. This exposes imperfections at crucial points during the fabrication process. This technology is fast and non-destructive. It probes the electrical properties of graphene or layered materials without direct contact.

Terahertz spectroscopy, a characterization technique that allows graphene-enabled devices to be made predictably and consistently, is crucial for accelerating large-scale production. Trust is built on quality control. Other innovations made possible by the Graphene Flagship include roll-to-roll graphene production and layered materials. The fabrication technology is now ready for the next step. Terahertz spectroscopy enables us to increase graphene production without compromising on quality.

Terahertz spectroscopy penetrates graphene film, allowing scientists to create detailed maps of the electrical quality without damaging or contaminating it. Credit: Peter Boggild, Graphene Flagship / DTU

Peter Boggild, Graphene Flagship partner DTU, says that this is the technology we needed to match the high-throughput production rates enabled by the Graphene Flagship. He adds that “terahertz spectrum in graphene manufacturing is going to become as common as X-ray scanning in hospitals.” “Thanks to terahertz spectroscopy, you can easily map even meter-scale graphene samples, which is impossible with other state-of-the-art techniques.” The Graphene Flagship is also studying how to use terahertz spectroscopy directly in roll-to-roll graphene production lines to speed up imaging.

This achievement was possible only through collaboration. Graphene Flagship researchers at academic institutions collaborated closely with graphene manufacturer partners AIXTRON and Graphenea. Boggild says, “This is the best method to ensure that our solution meets the needs of our end-users. This includes companies that produce graphene and other layered materials at industrial scales.” He adds that the publication is a detailed case study highlighting the reliability and versatility of terahertz spectroscopy for quality control. It should guide our colleagues in applying this technique to many industrially applicable substrates like silicon, sapphire, and silicon carbide.

Establishing standards for any new material is essential to make it safe and genuine. This will ensure that the product is reliable and consistent. The Graphene Flagship’s dedicated group focuses on standardizing graphene, measuring and analytical techniques, and manufacturing processes. Thanks to the Graphene Flagship Standardisation Committee’s efforts, the newly developed terahertz spectroscopy method could become a standard technical specification. Peter Jepsen, Graphene Flagship Partner DTU and co-author of the study, said that this would undoubtedly increase the adoption of the new technology. He explained, “This will outline how analysis can be done in a reproducible manner of graphene samples.” He concludes, “Terahertz spectrum is another step in increasing trust in graphene-enabled products.”

Amaia Zurutuza is co-author and Scientific Director at Graphene Flagship Partner Graphenea. She says: “At Graphenea, we are convinced that terahertz imagery can enable us to develop quality control techniques capable of matching manufacturing throughput requirements, providing relevant graphene information, which is crucial in our path toward the successful industrialization of graphene.”

Thurid Gspann is the Chair of the Graphene Flagship Standardisation Committee. He says the industry will soon adopt the terahertz [spectroscopy] method. It doesn’t require sample preparation and is a mapping method that allows you to analyze large areas quickly.

Marco Romagnoli is the Graphene Flagship Leader for Electronics and Photonics Integration. He adds: “The terahertz spectroscopy instrument for wafer-scale applications is a state-of-the-art, high TRL system that characterizes multilayer stacks on wafers containing CVD graphene. It is quick and accurate and gives the critical parameters of interest, such as carrier mobility and conductivity. This technical accomplishment is an excellent example of the benefits of being part of a significant collaborative effort like the Graphene Flagship.

Andrea C. Ferrari is Science and Technology Officer at the Graphene Flagship and Chair of its Management Panel. He adds, “Yet another Graphene Flagship scientist is pioneering a new characterization method to facilitate graphene technology development. This will allow us to continue our innovation and technology roadmap. It will also benefit industrial graphene uptake in a wide variety of applications.


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