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

Jean-Marie Vallerot (1) , Xavier Bourrat (1, 2) , Arnaud Mouchon (1) , Georges Chollon (1)

1 LCTS - Laboratoire des Composites Thermostructuraux
2 ISTO - Institut des Sciences de la Terre d'Orléans

In pyrocarbon materials, the width of the Raman D band (FWHMD) is very sensitive to low energy structural defects (e.g., disorientations of the graphene layers). The correlation between the two parameters, FWHMD and OA (as derived from selected area electron diffraction: SAED), has allowed to differentiate various pyrocarbons unambiguously. Furthermore, the optical properties of pyrocarbons, i.e., the extinction angle, the optical phase shift and the ordinary and extraordinary reflectance, have been accurately determined at 550 nm by means of the extinction curves method. These results are completed by in-plane and out-of-plane dielectric constant measurements by angular resolved EELS. Moreover, the hybridization degree of the carbon atoms has been assessed by the same technique. About 80% of the carbon atoms of the pyrocarbons have a sp2 hybridization. The lack of pure sp2 carbon atoms, as compared to graphite, might be explained by the presence of sp3-like line defects.

Mots clés: Pyrolytic carbons; Optical microscopy; Raman spectroscopy; Electron energy-loss spectroscopy

Domaines: Géophysique [physics.geo-ph]

Jean-Marie Vallerot, Xavier Bourrat, Arnaud Mouchon, Georges Chollon. Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques. Carbon, 2006, 44 (9), pp.1833-1844. ⟨10.1016/j.carbon.2005.12.029⟩. ⟨insu-00159174⟩