Length characterization of DNA-wrapped carbon nanotubes using Raman Spectroscopy*

The systematic resonance Raman study has been carried out on DNA-wrapped SWNTs of different lengths using several different values of laser excitation energy. The correlation observed between the intensity ratio of the D -band and G-band features (I$_{D}$/I$_{G})$ and the average nanotube energy lengths indicates that nanotube length can be used as the dominant structural parameter in Raman characterization, and that the I$_{D}$/I$_{G}$ ratio can be used as a qualitative gauge for estimating the average nanotube length. By systematically varying the laser excitation energy, we have also found that the I$_{D}$/I$_{G}$ ratio strongly depends on whether the tubes are metallic or semiconducting, as well as on the laser excitation energy. Further directions for this research will be presented. The authors gratefully acknowledge support for this research from the National Science Foundation grant DMR-04-05538.