Infrared-active phonons in carbon nanotubes

The aim of the present paper is to identify the main infrared vibrational features of carbon nanotubes. In this goal, infrared experiments have been performed on different well-characterized single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) as well as graphite and carbon aerogel. The comparison between the experimental spectra measured on these different samples allows us to identify the infrared-active modes of carbon nanotubes. In SWCNTs, the tangential modes are located around $1590{\mathrm{cm}}^{-1}$ and the radial mode around $860{\mathrm{cm}}^{-1}$. This latter mode vanishes in the infrared spectrum of DWCNTs. Finally, in the infrared spectra of all the carbon nanotubes investigated, a band around $1200{\mathrm{cm}}^{-1}$ is evidenced and assigned to the $D$-band (disorder-induced band).

Figure 1

The transmittance ir spectra of carbon aerogel (top), SWCNT sample (middle), and graphite (bottom). The spectra have been shifted for clarity.

Figure 2

Comparison between the transmittance ir spectra measured on several carbon materials. From top to bottom: graphite (curve 1), SWCNTs (curves 2–6), and carbon aerogel (curve 7). (a) The radial mode range, (b) the $900–1300{\mathrm{cm}}^{-1}$ range, and (c) the TM range. The spectra have been shifted for clarity.

Figure 3

Comparison between the transmittance ir spectra measured on a DWCNT sample (top) and a SWCNT sample (bottom). (a) The radial mode range, (b) the $900–1300{\mathrm{cm}}^{-1}$ range, and (c) the TM range. The spectra have been shifted for clarity.