Electrochemical switching of the Peierls-like transition in metallic single-walled carbon nanotubes

The high-energy vibrational modes of metallic carbon nanotubes are believed to be softened compared to the semiconducting ones by a Peierls-like transition. The Raman modes, when excited with a red laser to enhance the metallic tubes, were found to exhibit an exceptionally high sensitivity to electrochemical doping. Our data may be interpreted as controlling the Peierls-like instability in metallic tubes with the applied potential. We also discuss the limits of applicability of the double-layer charging model and show Raman evidence for a hysteretic transition to a chemical doping regime.

Figure 1

SEM image of the investigated SWNT bundles

Figure 2

(Color online) (a) Raman spectra at $1.95\mathrm{eV}$ excitation energy of the high-energy mode (HEM) at several potentials applied to the SWNT electrode in $1\mathrm{M}$ $\mathrm{N}{\mathrm{H}}_4\mathrm{Cl}$ aqueous solution. (b) The frequency of the main HEM peak P1 as a function of the applied potential (circles, blue). (c) Same as (b) for the peaks P3 (triangles, red) and P4 (diamonds, red).

Figure 3

(Color online) (a) Integrated Raman intensity of the peaks $\mathrm{P}3+\mathrm{P}4$ of metallic SWNTs (triangles, red) and $\mathrm{P}1+\mathrm{P}2$ (circles, blue) of the high-energy band as a function of the applied potential. See text and Fig. 1 for explanation on the peak notations. (b) Total Raman intensity of the high-energy band with $1.95\mathrm{eV}$ excitation as a function of the applied potential. (c) Same as (b) for $2.41\mathrm{eV}$ excitation.

Figure 4

(Color online) (a) Raman spectra at $1.95\mathrm{eV}$ excitation of the HEM upon electrochemical doping at several high potentials. (b) Measured frequencies of the peak P1 (diamonds, blue) and the newly appearing peak P0 (circles, black) at $1598{\mathrm{cm}}^{-1}$ as a function of the applied potential. Both arrows mark the sequence of increasing-releasing potential in the hysteresis of P1.