Phonon softening in individual metallic carbon nanotubes due to the Kohn Anomaly.
We have studied the line shape and frequency of the G band Raman modes in individual metallic single walled carbon nanotubes (M-SWNTs) as a function of Fermi level (epsilonF) position, by tuning a polymer electrolyte gate. Our study focuses on the data from M-SWNTs where explicit assignment of the G- and G+ peaks can be made. The frequency and line shape of the G- peak in the Raman spectrum of M-SWNTs is very sensitive to the position of the Fermi level. Within +/- variant Planck's over 2piomega/2 (where variant Planck's over 2piomega is the phonon energy) around the band crossing point, the G- mode is softened and broadened. In contrast, as the Fermi level is tuned away from the band crossing point, a semiconductinglike G band line shape is recovered both in terms of frequency and linewidth. Our results confirm the predicted softening of the A-symmetry LO phonon mode frequency due to a Kohn anomaly in M-SWNTs.
Farhat
H
H
Department of Materials Science and Engineering, MIT, Cambridge, MA 02139, USA.
Son
H
H
Samsonidze
Ge G
GG
Reich
S
S
Dresselhaus
M S
MS
Kong
J
J
D018625:Microscopy, Atomic Force; D036103:Nanotechnology; D037742:Nanotubes, Carbon / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
D037742:Nanotubes, Carbon