The double-resonance Raman spectra in single-chirality (n, m) carbon nanotubes

Abstract

Single-chirality (n, m) carbon nanotubes exhibit the same richness in physics of graphene including an additional phenomenon: the quantum confinement of electrons and phonons along the nanotubes circumference. Raman spectroscopy has been employed for almost 20 years to study carbon nanotubes, but the effect of the quantum confinement on the double-resonance (DR) Raman process in a single-chirality carbon nanotube was not yet understood. In this work, Raman spectra of the 2D band in enriched nanotube samples were measured using more than 70 laser excitation lines in the visible range (1.87–2.71 eV), and simulations of the D and 2D Raman spectra of single-chirality nanotubes were performed considering the quantum confinement along the nanotube circumference. We show that each single-chirality nanotube exhibits a series of non-dispersive D and 2D Raman peaks, which are not necessarily enhanced by resonances with optical transitions between van Hove singularities. Our results provide a complete explanation of the DR Raman spectrum, including the D and 2D bands, at the specificity level of a single-chirality nanotube, and will allow for the correct interpretation of the DR spectra of carbon nanotubes in samples containing a distribution of different (n, m) nanotube species.