Local measurement of charge density in carbon nanotubes by Raman spectroscopy

The energies of the Raman G-band transitions in both metallic and semiconducting CNTs are renormalized by the electron-phonon interaction, leading to energy shifts in Raman spectra of gated CNT devices. In addition in metallic CNTs, the linewidth decreases sharply upon electrostatic doping because the Γ-point phonon can no longer decay into electronhole pairs when the Fermi level is removed by more than 1/2 the phonon energy from the K-point. Raman spectroscopy can therefore be used to locally measure charge density and capacitance of individual CNTs in a nanotube field-effect transistor. Experiments under bias reveal breaks in nanotubes and depleted nanotube segments close to the contacts. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.