Assignment of (n, m) Raman and optical features of metallic single-walled carbon nanotubes

Raman spectroscopy performed between 565 and 627 nm and also between 458- and 514.5-nm laser excitation was used to map the lowest-energy van Hove singularities of metallic single-walled carbon nanotubes suspended in aqueous solution using sodium dodecyl sulfate. The interband transitions of distinct metallic nanotubes were observed directly and assigned using a correlation of the diameter and radial breathing mode (RBM) in the Raman spectrum. The results were extrapolated to all metallic nanotubes using a generalized scaling derived from the tight-binding formalism and were shown to be valid for describing the electronic structure of semiconducting nanotubes as well. The model results are compared using excitation profiles outside of the above-reported scan ranges with excellent agreement between observed and predicted profile widths and transition energies.