Optical studies of finite length effects in short DNA-wrapped carbon nanotubes

In this study, a systematic resonance Raman study was carried out on samples of DNA-wrapped SWNTs with average lengths between 50 and 100nm using multiple laser excitation energies. The different Raman features have been studied in detail as a function of nanotube length and laser excitation energies. The ratio of the D-band to G-band intensities has been found to increase with decreasing average SWNT length and decreasing laser excitation energy. As the nanotubes becomes much shorter than 1/4 wavelength of light, distinct finite length effects are also observed in overtone and intermediate frequency modes between 400 and 1500cm$^{-1}$. The MIT authors acknowledge supports under the Dupont-MIT Alliance, and NSF Grant DMR 04-05538.