A methodology to optimize the quantification of sp2 carbon fraction from K edge EELS spectra

A methodology is presented to select a consistent method, using electron energy loss spectroscopy (EELS), to extract the fraction of sp2-bonded carbon atoms in carbonaceous materials. According to this methodology, a reliable method has to conjointly fulfill two criteria. The first one consists in verifying, on a perfect graphite sample, that the experimental evolution of R = Iπ*/(Iπ* + Iσ*)-ratios is in good agreement with the one theoretically predicted as a function of experimental settings. The second criterion consists in measuring sp2 fractions in amorphous carbon samples with a minimum of fluctuation. We test three commonly used R-extraction techniques, and we show that they exhibit some failures. We thus implement a more accurate R-extraction process that accounts for the predicted graphite R-evolution and exhibits a low intrinsic 4%-noise, as determined from the sp2 fraction fluctuation. Moreover, we check the transferability of our method on a wide range of EELS spectra, acquired with different experimental resolutions on samples exhibiting various sp2 contents.