Infrared spectra of individual semiconducting single-walled carbon nanotubes: Testing the scaling of transition energies for large diameter nanotubes

We have measured the low-energy excitonic transitions of chiral assigned individual large-diameter semiconducting single-walled nanotubes using a high-resolution Fourier transform photoconductivity technique. When photoconductivity is complemented by Rayleigh scattering spectroscopy, as many as five optical transitions can be identified on the same individual nanotube over an energy range of 0.3-2.7 eV. We find that well-established energy scaling relations developed for nanotubes of smaller diameter are not consistent with the measured low-energy transitions in large (1.8-2.3 nm) diameter nanotubes.