The longitudinal optical phonon of metallic nanotubes shifts by 23 cm−1 to lower energies when the nanotubes are deposited from a solution onto a substrate. The linewidth increases by 13 cm−1. The changes are explained in terms of shifts in the Fermi energy that influence the Kohn anomaly in the longitudinal optical phonon branch in metallic nanotubes. Using in situ electrochemical Raman measurements we show that the Fermi energy is 0.16 eV below its intrinsic value in metallic nanotubes in solution. Our results impact the application of Raman spectroscopy to distinguish between metallic and semiconducting tubes by examining the high-energy mode line shape.
