RAMAN STUDIES OF ELECTROSTATIC DOPING OF A THIN SINGLE-WALLED CARBON NANOTUBE BUNDLE

Abstract

In situ Raman measurements have been carried out on a thin bundle of single-walled carbon nanotubes (SWNTs) in field effect transistor configuration at various gate voltages. Two excitation lasers with the photon energy of 1.96 eV and 2.41 eV, respectively, are selected to excite the Raman scattering modes of metallic and semiconducting SWNTs in the bundle, respectively. For the metallic SWNTs, the G- Raman mode is found to shift to higher frequencies and narrow down its line shape at negative gate voltages, but be insensitive to positive gate voltages. These findings confirm that the Kohn anomaly exists in a thin SWNT bundle and that the LO phonon mode changes along with the position of the Fermi level in the metallic SWNTs. In contrast, semiconducting SWNTs do not show any observable changes in the Raman spectra.