Photophysics of carbon nanotubes

Abstract

This thesis reviews the recent advances made in optical studies of single-wall carbon nanotubes. Studying the electronic and vibrational properties of carbon nanotubes, we find that carbon nanotubes less than 1 nm in diameter exhibit dramatic changes in their electron and phonon dispersion relations due to the curvature of the nanotube sidewall and the enhanced electron correlation effects associated with one dimensionality. The optical transition energies in small-diameter carbon nanotubes show a strong dependence on their geometrical structure, as was first observed in the photoluminescence experiments. The frequencies of the Raman-active phonon modes also become very sensitive to the geometrical structure of small-diameter carbon nanotubes. In particular, certain phonon modes exhibit anomalous behavior that significantly affects resonance Raman spectra of small-diameter carbon nanotubes. We have developed the extended tight-binding and advanced force-constant models that properly take into account the curvature effects in the small-diameter limit. The many-body corrections are fitted to the photoluminescence and resonance Raman spectroscopy data.

(cont.) The resulting extended tight-binding model with semiempirical many-body corrections shows a good agreement with the experimental results. The electron-photon and electron-phonon transition matrix elements are calculated within the framework of the extended tight-binding model. Finally, the photoluminescence and Raman intensities in the graphene sheet and carbon nanotubes are calculated. The calculated intensities show a reasonable agreement with the experimental results and allow structural characterization of carbon nanotubes by their spectroscopic signatures.