Probing symmetry-breaking defects in polished graphitizable sp2 carbons using angle-resolved polarized Raman scattering

Raman scattering is commonly used to quantify defects in sp2 carbons, mostly based on the values of the double-resonant D-band intensity. It is well known that this peculiar band undergoes changes when the sp2 carbon is polished. However, the physical process behind this phenomenon is unclear so far. In this paper, we provide a deep understanding of the fundamental optical properties of the polishing-induced defects by combining angle-resolved polarized Raman scattering and theoretical calculations. We address the question regarding the types of these additional defects that participate in the intervalley double-resonance Raman process and contribute to the spatially inhomogeneous increase of the relative D-band intensity. The study was performed on anthracene-based coke pyrolyzed at 2000 degrees C and uses highly oriented pyrolytic graphite with known crystallographic orientations as a model material. The results shed light on the types of defects as well as the D-band peculiar behavior as a function of the spatial orientation of graphene layers dictated by polishing with respect to the fixed direction of the incident and scattered light. Moreover, the insignificant change in I2D/IG, the width and the position of the G band after polishing, and the insensitivity of less ordered carbons to this process are also discussed.