The Raman D/G Intensity Ratio in Graphitization Studies of Carbon Materials: A Three-Tier Structural Framework.

Raman spectroscopy is widely used to assess structural order in carbon materials, yet the Raman I(D)/I(G) intensity ratio is frequently interpreted as a measure of graphitization. This Perspective introduces a three-tier structural framework that relates Raman observables to the specific structural dimensions they probe. The I(D)/I(G) ratio reflects in-plane sp2 defect density and crystallite size, whereas graphitization requires the development of three-dimensional stacking coherence. These structural attributes are distinct. Examination of representative peer-reviewed studies published over the past decade shows that graphitization is often inferred from I(D)/I(G) despite accompanying X-ray diffraction (XRD) evidence indicating predominantly amorphous or turbostratic carbon. By contrast, the Raman 2D band, which is directly sensitive to interlayer coupling, is seldom reported. This Perspective clarifies the physical interpretation of Raman observables and presents a three-tier structural framework that aligns Raman- and XRD-based assessments of graphitization.