International interlaboratory comparison of Raman spectroscopic analysis of CVD-grown graphene

Abstract

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”.

International Interlaboratory Comparison of Thermogravimetric Analysis of Graphene-Related Two-Dimensional Materials

“…These parameters are as follows: (1) the number of mass loss steps, (2) thermal stability, (3) temperature of maximum mass change rate ( T p ) for each decomposition step, (4) the mass contents (%) of moisture, oxygen groups, carbon, combustible organic impurities, and (5) the mass content (%) of noncombustible residues. These parameters have been selected to combine the measurement of physical and qualitative and quantitative chemical properties of GR2Ms based on their practical relevance, complementarity with other ISO characterization methods and the developed procedures from both the authors and the literature. − , …”

Automated statistical analysis of raman spectra of nanomaterials

“…A recent interlaboratory study has concluded that the standard deviation of peak widths of graphene spectra, especially for the 2D band, are substantially reduced if Voigt fitting is used instead of Lorentzian. 68 A Voigt function is a convolution of a Gaussian and a Lorentzian function and it captures better the broadening of the 2D mode resulting from doping, strain variations or increasing defect density since the gaussian component of the Voigt can accommodate the change in the peak tails. Therefore, we have developed an alternative code where Lorentzian fitting functions are replaced by a pseudo-Voigt functions as defined in OriginPro 2020 (‘ PsdVoigt1 ’):where y 0 is a constant background, A is the peak area, w is the FWHM, x 0 is the peak center and m u the profile shape-parameter (or gaussian weight/fraction).…”

Moving from Raman Spectroscopy Lab towards Analytical Applications: A Review of Interlaboratory Studies

“…Instruments 2023, 7, 30 2 of 16 These advantages made Raman spectroscopy a tool used in numerous fields, both in research and technology [5]. Speaking of areas such as the pharmaceutical industry [2], medicine [6,7], analytical chemistry [8][9][10][11], mineralogy [12,13], materials science [14], historical research [9,15], and even forensic science [16], it has revealed many applications. It is easy to see the importance of this technique, but is it suitable for its wide use in highly regulated environments?…”