Vanishing of the Breit-Wigner-Fano Component in Individual Single-Wall Carbon Nanotubes

In order to decide definitely on the dependence of the intensity of the Breit-Wigner-Fano (BWF) component with the size of the bundle, we have measured the radial breathing modes and tangential modes (TMs) of well defined metallic individual single-wall carbon nanotubes (SWCNTs) and individual SWCNT bundles. In this aim, a complete procedure including the preparation of the substrates, the sample preparation, atomic-force-microscopy imaging and Raman spectroscopy has been developed. From this procedure, we show unambiguously that the BWF component vanishes in isolated metallic SWCNTs. In other words, the observation of a BWF component in the TM bunch is an intrinsic feature of the metallic SWCNT bundle.

Figure 1

Atomic-force-microscopy image of a $5\times 5\mu {\mathrm{m}}^2$ area of the sample. An isolated SWCNT is located between the two markers (triangle and point) in the region delimited by the white square. The inset shows an average height profile of this tube obtained from a $1\times 1\mu {\mathrm{m}}^2$ AFM image.

Figure 2

RBM (a),(b) and TM (a′),(b′) ranges of the Raman spectrum of the individual 7 nm bundle (a),(a′) and isolated 1.27 nm SWCNT (b),(b′) collected using $E_{\mathrm{Laser}}=1.92\mathrm{eV}$ ($\lambda =647.1\mathrm{nm}$). The single line in the RBM range is fitted by a Lorentzian profile. Each line of the TM bunch is fitted by a Lorentzian, except the broad and asymmetric low-frequency band in the spectrum of the bundle that is fitted by using a BWF line shape (see text).

Figure 3

RBM (a),(b),(c) and TM (a′),(b′),(c′) ranges of the Raman spectrum of the individual 4 nm bundle (a),(a′), isolated 1.33 nm SWCNT (b),(b′) collected using $E_{\mathrm{Laser}}=1.92\mathrm{eV}$ ($\lambda =647.1\mathrm{nm}$), and isolated 1.33 nm SWCNT (c),(c′) collected using $E_{\mathrm{Laser}}=2.41\mathrm{eV}$ ($\lambda =514.5\mathrm{nm}$). The line shapes used in the fitting procedure are the same as in Fig. 2.

Figure 4

RBM (a),(b) and TM (a′),(b′) ranges of the Raman spectrum of the individual 7 nm bundle (a),(a′) and 4 nm bundle (b),(b′) collected using $E_{\mathrm{Laser}}=2.41\mathrm{eV}$ ($\lambda =514.5\mathrm{nm}$).