Researchers at The University of Manchester, working with the UK’s National Physical Laboratory (NPL) and 15 international partners, have developed a new protocol, using transmission electron microscopy (TEM), which is meant to underpin a new ISO technical specification for graphene.
The results of the large interlaboratory selected area electron diffraction (SAED) comparison study, where the collaborating laboratories measured and analyzed nominally identical samples of chemical vapor deposited (CVD) graphene, were recently presented. Large variations were observed in the measured ratios of diffraction spot intensities, with the largest variance associated with poor quality SAED data resulting from poor specimen handling and storage. To inform the reliable determination of monolayer thickness from SAED patterns, the team provided a description of best practice for specimen handling, TEM operation, data collection and analysis. The results of this work have been directly incorporated into ISO/TS 21356-2 for the characterization of graphene sheets.
The team found that when this methodology is followed, monolayer graphene can be distinguished from bilayer or thicker material with high confidence where analysis of a single SAED pattern gives I{-2110}/I{1-100}<1.2, even in the absence of precise specimen tilting.
“To incorporate graphene and other 2D materials into industrial applications, from light-weight vehicles to sports equipment, touch screens, sensors and electronics, you need to know you’re working with the right material. This study sets a global benchmark that industry can trust,” said Dr. William Thornley, who worked on the research during his PhD.
“Electron diffraction has long been used to distinguish monolayer from few‑layer graphene, but it’s often applied without a full treatment of uncertainties. By collaborating across 15 leading labs. including the original pioneers, we’ve mapped the pitfalls and shown how to get reliable results” added Dr. Evan Tillotson.
“We’ve designed this protocol so it works in real labs, not just in specialist centers. And for organizations without TEM capability, we can provide measurements commercially through our partnership with the Royce Institute,” said Professor Sarah Haigh, Professor of Materials.
The findings are used directly within the ISO/TS 21356-2 international standard, currently in press and expected to be published in 2026. “This work builds on the NPL Good Practice Guide 145 'Characterization of the Structure of Graphene’ developed in partnership with the University of Manchester, and one of NPL's most downloaded guides.", notes Dr. Andrew Pollard, Principal Scientist of the Surface Technology Group and Advanced Materials Strategy Lead at NPL.
