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

TL;DR

This study combines Raman spectroscopy, electron diffraction, and other techniques to quantitatively analyze the structural and optical properties of laminar pyrocarbons, revealing correlations between defects and optical behavior.

Contribution

It introduces a comprehensive multi-technique approach to differentiate pyrocarbon structures and assess their hybridization and optical properties.

Findings

FWHMD correlates with OA, differentiating pyrocarbons.

Approximately 80% of carbon atoms are sp2 hybridized.

Optical properties measured at 550 nm provide detailed insights.

Abstract

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.