Polarization effects in Raman spectroscopy of light-absorbing carbon

Abstract

Raman spectroscopy is widely used for characterization of carbon-based materials including light-absorbing carbonaceous (LAC) matter. However, information on polarization properties of these materials are generally lacking, and often the polarization characteristics of experiments are not presented in the literature thereby giving uncertainty to presented data. In this work, the polarization properties of various LACs are studied using Raman spectroscopy. The Raman spectra have been compared while varying the relative polarization, particularly the relative direction of the electric field between the incident light and the detected scattered light. Specifically, the intensity ratio between the D1 and G peaks (ID1/IG) was analyzed in parallel and perpendicular polarization configurations for samples taken from a sooting flame, in the exhaust of a soot generator and carbon blacks. In this work, the parallel and perpendicular polarization configurations mean that the polarization of the detected scattered light is parallel and orthogonal, respectively, to the linearly polarized incident light. It was found that the (ID1/IG) ratio decreased in the more ordered carbonaceous structures when changing the polarization configuration from parallel to perpendicular. Additionally, based on the depolarization ratios (Dp < 0.75), the prominent Raman peaks of LAC were found to originate from totally symmetric vibrations. For the G peak, the depolarization ratio was measured to be in the range 0.46–0.56 for all LAC materials.