Raman spectroscopy of nondispersive intermediate frequency modes and their overtones in carbon nanotubes

Abstract

We performed resonance Raman spectroscopy on HiPCO-produced single-walled carbon nanotubes in the spectral region of 846 and , using laser excitation energies between and . We observe a characteristic peak around and its overtones around 1692. Especially the latter was controversially discussed in the past and has been assigned to a double-resonant Raman process involving two oTO phonons. We demonstrate that both peaks slightly depend on the excitation laser energy by means of their shape, intensity, and peak position. Following the model proposed by Dobardžić et al., we relate both peaks to oTO -point phonons. As we analyze both, the first-order band and its overtone simultaneously, we are able to provide a unified explanation of these low-intensity Raman bands in carbon nanotubes. Raman spectrum of an HiPCO-produced buckypaper carbon nanotube sample at 2.33 eV laser energy. Both insets show a magnification of the oTO-related first- and second-order Raman bands, which we discuss in this article.