sp² hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials. Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects and has been widely used since the 1980s. Depending on the material studied, some specific spectroscopic parameters (e.g., band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects. This paper is addressed first to (but not limited to) the newcomer in the field, who needs to be guided due to the vast literature on the subject, in order to understand the physics at play when dealing with Raman spectroscopy of graphene-based solids. We also give historical aspects on the development of the Raman spectroscopy technique and on its application to sp² hybridized carbons, which are generally not presented in the literature. We review the way Raman spectroscopy is used for sp² based carbon samples containing defects. As graphene is the building block for all these materials, we try to bridge these two worlds by also reviewing the use of Raman spectroscopy in the characterization of graphene and nanographenes (e.g., nanotubes, nanoribbons, nanocones, bombarded graphene). Counterintuitively, because of the Dirac cones in the electronic structure of graphene, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism. This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials. We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of Raman spectra, and discuss samples to be studied in the future with some complementary technique (e.g., high resolution transmission electron microscopy) in order to disentangle the influence of structure and defects.

In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon ($a$ -C:H) films. $a$ -C:H films with a hydrogen content varying from 29 to $47\text{at}\text{.}\%$ have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures $\left(<120°\text{C}\right)$ applying a wide range of bias voltage, $V_b$ , $\left(-300\text{V}<V_b<+100\text{V}\right)$ . With the application of high negative $V_b$ , the $a$ -C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer- to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C–H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressions are inferred for the amount of bonded hydrogen as a function of the experimental spectroscopic parameters, i.e., the integrated area of the IR C–H stretching band at about $2900{\text{cm}}^{-1}$ , the PL background in visible Raman spectra, and the XANES intensity of the ${\sigma }^{\ast }\text{-CH}$ peak.