Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

摘要

In pyrocarbon materials, the width of the Raman D band (FWHMD) is verysensitive to low energy structural defects (e.g., disorientations of thegraphene layers). The correlation between the two parameters, FWHMD and OA (asderived from selected area electron diffraction: SAED), has allowed todifferentiate various pyrocarbons unambiguously. Furthermore, the opticalproperties of pyrocarbons, i.e., the extinction angle, the optical phase shiftand the ordinary and extraordinary reflectance, have been accurately determinedat 550 nm by means of the extinction curves method. These results are completedby in-plane and out-of-plane dielectric constant measurements by angularresolved EELS. Moreover, the hybridization degree of the carbon atoms has beenassessed by the same technique. About 80% of the carbon atoms of thepyrocarbons have a sp2 hybridization. The lack of pure sp2 carbon atoms, ascompared to graphite, might be explained by the presence of sp3-like linedefects.