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The heterogeneous nature of mass-produced 2D material’s nanoflakes requires analysis of size and shape parameters: their distributions around the desired values are essential for production and characterization. In this work, we obtain analytical expressions and behaviors of statistical distributions of experimentally extracted size and shape parameters of nanoflakes obtained by liquid-phase exfoliation. The collected data are open and can be mathematically handled to be analyzed through different associations in different scales, such as the logarithm of the length/thickness (r) and length/width (r L) aspect ratios. We find that ln­(r), a shape parameter, follows nearly Gaussian distributions, being an efficient fingerprint to characterize the material type and processing. On the other hand, the logarithms of thickness and volume follow asymmetric distributions with specific asymptotic behaviors, called exponential-power-Gaussian functions, but centrifugation turns both nearly Gaussian-distributed. Finally, the logarithm of the length/width aspect ratio, ln­(r L), an in-plane shape parameter, was found to follow the single-parameter probability density distribution xe–λx 2 . The method detected that centrifugation enhances, by up to threefold, the percentage of flakes with large length/width ratios. This statistical methodology can be incorporated into the quality control of mass production of 2D nanoflakes, whose target applications can be found across the fast-growing nanomaterials’ industry.

There is a pressing need for reliable, reproducible and accurate measurements of graphene’s properties, through international standards, to facilitate industrial growth. However, trustworthy and verified standards require rigorous metrological studies, determining, quantifying and reducing the sources of measurement uncertainty. Towards this effort, we report the procedure and the results of an international interlaboratory comparison (ILC) study, conducted under Versailles Project on Advanced Materials and Standards (VAMAS). This ILC focusses on the comparability of Raman spectroscopy measurements of chemical vapour deposition (CVD) grown graphene using the same measurement protocol across different institutes and laboratories. With data gathered from 17 participants across academia, industry (including instrument manufacturers) and national metrology institutes, this study investigates the measurement uncertainty contributions from both Raman spectroscopy measurements and data analysis procedures, as well as provides solutions for improved accuracy and precision. While many of the reported Raman metrics were relatively consistent, significant and meaningful outliers occurred due to differences in the instruments and data analysis. These variations resulted in inconsistent reports of peak intensity ratios, peak widths and the coverage of graphene. Due to a lack of relative intensity calibration, the relative difference reported in the 2D- and G peak intensity ratios (Ι_2D/Ι_G) was up to 200%. It was also shown that the standard deviation for Γ_2D values reported by different software packages, was 15× larger for Lorentzian fit functions than for pseudo-Voigt functions. This study has shown that by adopting a relative intensity calibration and consistent peak fitting and data analysis methodologies, these large, and previously unquantified, variations can be significantly reduced, allowing more reproducible and comparable measurements for the graphene community, supporting fundamental research through to the growing graphene industry worldwide. This project and its findings directly underpin the development of the ISO/IEC standard “DTS 21356-2 - Nanotechnologies - Structural Characterisation of CVD-grown Graphene”.

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A primitive cubic lattice composed of 1,000 atoms has 488 surface sites. By definition, every atom in a strictly two-dimensional single-layer lattice composes its surface. These surface atoms are the ones that undergo chemical interactions with the surrounding medium, thereby defining the functionalities of the nanostructure. As such, one of the most important morphological properties of nano-objects is the extremely large specific surface area that enhances their levels of reactivity. Here, we introduce an optical spectroscopy method to measure the surface area concentration, ρA, of mass-produced graphene nanoflakes in liquid dispersions. The information is accessed from the quenching of the fluorescence signal from the dye molecules dispersed in the medium. We found that the quantum efficiency of the fluorescence signal decays exponentially with the concentration of graphene’s surface area, the decay rate being independent of the degree of exfoliation. If the mass concentration ρ is known by other means, the specific surface area can be extracted from the ratio ρA/ρ. The measurements can be performed directly in liquid suspensions of nanoflakes, being highly applicable to the quality control of mass-produced two-dimensional nanomaterials, especially by means of mechanically assisted liquid-phase exfoliation.

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