Longitudinal Optical Phonons in Metallic and Semiconducting Carbon Nanotubes

Abstract

We analyze the high-energy Raman modes, G+ and G-, in a pair of one metallic and one semiconducting nanotubes. By combining Rayleigh scattering with Raman resonance profiles of the radial breathing mode and the high-energy modes, we show that the observed G- and G+ peaks can originate from longitudinal optical phonons of different tubes. The G- peak is the longitudinal mode of the metallic tube; it is broadened and downshifted due to strong electron-phonon coupling in the metallic nanotube. The G+ peak is due to the longitudinal mode in the semiconducting tube. This result resolves an ongoing debate in the literature.

Carbon nanotubes for ultrafast fibre lasers

“…It is broadened and shifted to the low-frequency region, due to the presence of free electrons. In the case of s-SWNTs, the Gmode refers to tangential optical phonons, whereas G + refers to longitudinal optical phonons [189]. Splitting of the tangential mode can be used for diameter characterisation.…”

Influence of architecture on the Raman spectra of acid-treated carbon nanostructures

“…For the sample SW1.5 a change in the FWHM was only evident when using the harsher acid treatment (B); for all other CNSs (Figure 5a and b) their scattering bars (standard deviation) overlap. The decrease of the FWHM of the G band for SWCNTs can be explained by the upshift of the longitudinal optical mode (usually $1540 cm À1 from the metallic tubes) and disruption of the asymmetric line shape upon strong oxidation and heavy functionalisation [13,36]. The FWHM of the D band, Figure 6, was found between 46 and 101 cm À1 with the maximum value corresponding to CF500 and the minimum to CF500G.…”

Polarized surface-enhanced Raman spectroscopy of suspended carbon nanotubes by Pt-Re nanoantennas

“…The intensity of the Raman signal measured on a bare CNT depends on the difference between the incidenthω L (or the scattered hω L ±hω q ) photon energy and the energy separation E ii between VHSs. The width of such resonance windows is roughly of the order of 200 meV for the G mode and around 50 meV for the radial breathing mode (RBM) [27,31]. If the difference between incident (or scattered) photon and the transition energy E ii is larger than the above values, then the Raman signal is drastically suppressed.…”