Raman spectroscopic studies on well-defined carbonaceous materials of strong two-dimensional character

TLDR

Using 514 nm Raman spectroscopy with a quantitative protocol, the authors measured first- and second-order spectra of five graphite types, including single-crystal, HOPG, two faulted, and a turbostratic sample. The study shows that complete c‑axis disorder markedly enhances the E2g‑mode intensity, that the 2700 cm⁻¹ doublet remains resolved even with short AB sequences, and that the 1355 cm⁻¹ peak reflects finite in‑plane domain size rather than disorder, offering a more sensitive probe than X‑ray diffraction.

Abstract

Using 514 nm radiation and a careful experimental protocol allowing us to make quantitative intensity analyses, we have examined the first- and second-order Raman spectra of five varieties of graphite. These include single-crystal graphite and highly oriented pyrolytic graphite as references, then two with a significant content of c-axis translation faults introduced through grinding and exfoliation, and a last sample which is purely turbostratic. We show that full c-axis stacking disorder results in a strong increase of the scattered E2g-mode intensity. We have further shown that even in those strongly disordered stacking sequences, but in which the AB sequence persists over only a few layers, the doublet around 2700 cm−1 is resolved. We argue against assigning the peak around 1355 cm−1 to “disorder,” as is so often done, but to the finite in-plane domain size as proposed a number of years ago; moreover, we suggest that this peak is a more sensitive probe of such small domains than is x-ray diffraction.