Raman $G$ band in double-wall carbon nanotubes combining $p$ doping and high pressure

We use sulfuric acid as pressure medium to extrapolate the $G$-band position of the inner and outer tubes of double-wall carbon nanotubes. Keeping the $G$-band position of the inner and outer tubes constant, we can determine the fraction of double-wall and single-wall tubes in samples containing a mixture of the two. $A$-band-related electronic interwall interaction at $1560{\text{cm}}^{-1}$ is observed, which is associated with the outer tube walls. This band is observed to shift with pressure at the same rate as the $G$ band of outer tubes and is not suppressed with chemical doping. Differences in the interwall interaction is discussed for double-wall carbon nanotubes grown by the catalytic chemical-vapor method and double-wall carbon nanotubes obtained through transformation of peapods.

Figure 1

(Color online) Transmission electron microscopy images of DWs.

Figure 2

Effect of doping with ${\text{H}}_2{\text{SO}}_4$ on Raman spectra of SW and DWs excited at 633 nm.

Figure 3

$G$ band of DW sample for pressures up to 9.5 GPa using ${\text{H}}_2{\text{SO}}_4$ as pressure transmitting medium.

Figure 4

$G$-band position of inner and outer tubes in function of pressure (left) and intensity ratio (right).

Figure 5

Doped and undoped Raman spectra of $G$ band of DW sample on three different locations (A, B, and C): Stokes (S) and anti-Stokes (AS) spectra after including the Bose-Einstein $\left(T=775\text{K}\right)$ and ${\omega }^4$ factors.

Figure 6

DW spectra excited with red wavelengths and fitted with the parameters reported in Table . Arrows indicate that a band at 1550 or $1610{\text{cm}}^{-1}$ was used. Laser power and objective power ($\times 40$ or $\times 20$) are also indicated.