Abstract Submitted to the NANOTUBE'05 Conference:

Two recent advances in the application of laser-based techniques to characterize thee fundamental optical properties of single-walled carbon nanotubes (SWNTs) will be presented. The first concerns the determination of the strength of the excitonic interactions in SWNTs. Recent theoretical treatments of the excited states in SWNTs predict that strong electron-hole interactions yield excitons with large binding energies and that the optical resonances in absorption and emission correspond to excitonic transitions. A direct determination of the exciton binding energy has, however, been lacking. Here we show how the distinct selection rules for two-photon spectroscopy allow us to identify the excited states of the SWNT excitons and to deduce thereby exciton binding energies [1]. Values as large a 400 meV are obtained, corresponding to a significant appreciable fraction of the SWNT band-gap energy. The second topic involves a new and general approach to the optical spectroscopy of individual SWNTs. The method is that of elastic or Rayleigh light scattering [2]. The scattering cross-section as a function of photon energy exhibits resonances for any optical transition, whether in a metallic or semiconducting tubes. Applications to examine tube-tube interactions, polarization effects, and changes in SWNT structure along the tube axis will be presented.

[1] F. Wang, G. Dukovic, L. E. Brus, and T. F. Heinz, Science 308, 838 (2005).
[2] M. Y. Sfeir, F. Wang, L. M. Huang, C. C. Chuang, J. Hone, S. P. O'Brien, T. F. Heinz, and L. E. Brus, Science 306, 1540 (2004).

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