Discrimination of Allotropic Forms of Carbon by Laser-Induced Breakdown Spectroscopy (LIBS)

In this study, we introduce a novel method for distinguishing among allotropic forms of carbon using laser-induced breakdown spectroscopy (LIBS) in air. We used the time evolution of CN and C2 molecular emission spectra to characterize various carbon allotropes, including graphite, fullerene, nanotubes, and amorphous carbon. To differentiate among these carbon samples, we employed principal component analysis (PCA). Our findings reveal significant differences in the plasma molecular emission of various carbon-based materials, offering new insights into their characterization. Notably, we observed strong emission signals from the (1–0), (0–0), and (0–1) C2 bands across all carbon allotropic forms during the early stages of plasma formation (less than 2 μs). In contrast, aromatic hydrocarbon samples exhibited more pronounced emissions at later moments in the plasma (around 4 to 12.8 μs). Overall, our time-resolved LIBS approach, combined with chemometric tools, provides a reliable and rapid way of identifying different allotropic forms of carbon.