Raman and SERS studies of carbon nanotube systems

In this paper, we report on Raman studies carried out on different carbon nanotube systems, namely single-walled and multi-walled carbon nanotubes and polymer/nanotube composites. We focus on different types of interactions which can take place in these materials. In single-walled nanotubes, the introduction of van der Waals interactions between tubes when arranged in bundles leads to an upshift of the radial breathing mode (RBM) ranging from 11 to 16 cm⁻¹ depending on the size of the bundle. In multi-walled carbon nanotubes, similar interactions between concentric tubes permit to interpret the low frequency Raman modes. In composites, PMMA/nanotubes, an upshift of the RBM is also observed, explained by the dynamical strain applied by the polymer on the bundles, in response to the breathing vibration. In addition, surface enhanced Raman scattering experiments have demonstrated the occurrence of interfacial reactions between the nanotubes and the metallic support. This is put in evidence by the degradation of tubes, especially metallic ones, and reconstruction of C₆₀-like molecules are in some cases observed.