New standard for measuring the flatness of graphene

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Researchers from Graphene Flagship partner RWTH Aachen University and the Graphene Flagship Standardization Committee have announced a new IEC standard for assessing the strain uniformity of single-layer graphene using Raman spectroscopy.

While considered to be the ultimate conductor research has shown that the electrical and the structural quality of graphene are intimately connected, and that nanoscale lattice deformations caused by surface corrugations can limit the mobility of electrons in graphene. Therefore, controlling the flatness of a graphene sheet is fundamental for the fabrication of high-quality graphene layers for electronic devices – and the possibility of measuring this parameter with a simple and fast method is a major technological advantage. The new standard for detecting graphene flatness, pioneered by the Graphene Flagship and published by the International Electrotechnical Commission (IEC), is intended to speed up the manufacture and implementation of single-layer graphene.

The method used to measure graphene’s flatness is Raman spectroscopy, a standard tool of graphene research. This technique is fast, non-destructive and well understood, especially if the sample under evaluation consists of single-layer graphene. It allows distinguishing between single and few-layer graphene, and it helps to determine the doping of a graphene, the amount of mechanical strain and defects in the lattice.

In 2015, Graphene Flagship researcher Christoph Stampfer at RWTH Aachen University, Germany, showed that Raman spectroscopy also contains unambiguous information on the amount of nanometer-scale strain variations in a graphene sheet, directly correlated to flatness.

“It was clear that this result had the potential for setting the basis of an internationally recognised standard for the strain uniformity of graphene”, said Norbert Fabricius, from International Standards Consulting.

The measurement is based on statistical interpretations of the linewidth of the characteristic 2D-peak generated by single-layer graphene.

“The strain uniformity parameter is a figure of merit that quantifies the influence of nanometer-scale strain variations on the electronic properties of the layer. It gives an upper limit on the electronic performance of the characterized graphene. It can therefore help manufacturers to classify their material and decide whether or not it is potentially suitable for various applications”, explained Fabricius.

The new standard was published by the EIC in October 2021 and is an example of the work supported by the Graphene Flagship Standardization Committee, currently chaired by Thurid Gspann from Graphene Flagship partner Karlsruhe Institute of Technology, Germany.

“A standard must meet the different needs of different stakeholders: researchers, manufacturers, and buyers”, said Gspann. “In the Committee we mediate the discussion between different actors to find consensus on the specifications of the standard, we support the scientific work that forms the backbone of the standard, and we link to international organisations such as the International Organization for Standardization (ISO) or, in this case, the IEC.

“Established standards can increase efficiency, reduce risks and costs, and catalyse innovation. This particular standard will allow manufacturers to certify that their material is in principle suitable for applications that crucially depend on the electronic quality of graphene, such as high-frequency transistors and broad-band receivers. This can accelerate the appearance of this type of devices onto the market.”