Origin of the Breit-Wigner-Fano lineshape of the tangentialG-band feature of metallic carbon nanotubes

Abstract

A detailed line-shape analysis of the tangential G-band feature attributable to metallic single-walled carbon nanotubes is presented. Only two components are needed to account for the entire G-band feature for metallic nanotubes. The higher-frequency component has a Lorentzian line shape, and the lower one has a Breit-Wigner-Fano ͑BWF͒ line shape. Through comparisons of the Raman tangential G-band spectra from three different diameter distributions of carbon nanotubes, we find that both the frequency and linewidth of the BWF component are diameter dependent and show functional forms consistent with theory. The nanotube curvature is responsible for both the frequency differences between the two components of the characteristic metallic G-band spectrum and the BWF coupling of the lower-frequency component. Surface-enhanced Raman spectroscopy studies provide supporting evidence that the phonon BWF coupling is to an electronic continuum.

Reversible, Band-Gap-Selective Protonation of Single-Walled Carbon Nanotubes in Solution

“…For all nanotubes, the Raman tangential modesa line near 1600 cm -1 shift arising from the C-C vibrations in sp 2 hybridized systemsssplits into high-and low-frequency phonons because the force constants for these bonds are larger in the direction parallel to the tube length than in the orthogonal direction. For metallic nanotubes, the latter is allowed to couple to the continuum of electronic states near the Fermi level, creating a broadened and low-frequency-shifted Breit-WignerFano (BWF) line shape: 12 where Γ, q, and ω o are broadening, line shape, and frequency renormalization parameters, respectively. Figure 2a shows this low-frequency BWF feature adjacent to a Lorentzian line shape that represents the remaining tangential modes.…”

Resonance Raman spectroscopy in one-dimensional carbon materials

“…This difference in line shape between M and S SWNTs is best observed in SWNT bundle samples since the coupling of the conduction electrons to phonons through a plasmon excitation is enhanced by intertube interactions (Kataura et al 1999, Brown et al 2001. By measuring the Raman spectra of nanotube bundles through varying E laser , as shown in Fig.…”

Low-energy electron irradiation of preheated and gas-exposed single-wall carbon nanotubes

“…[16], these correspond to the E2g TO , (A1g+ E1g) TO , (A1g+ E1g) LO , and E2g LO resonance modes of semiconducting SWCNTs, respectively. In addition, there is a small BWF peak at around 1521 cm − 1 and Lorentzian at around 1585 cm − 1 that are assigned to the LO and TO modes of metallic SWCNTs, respectively [24]. Figure 46 shows the effects of pre-heating laser ablation grown SWCNT samples in situ.…”

“…Peak assignments and symmetries are extrapolated from previous studies [20]. The BWF curve is attributed to phonon modes of A1g symmetry in metallic nanotubes and is asymmetric due to electron phonon coupling [24]. The most likely source of this curve in the samples comes from the metallic nanotubes with E11 M transition.…”