Electronic properties of barium-intercalated single-wall carbon nanotubes

The structural and electronic properties of barium-intercalated single-wall carbon nanotubes were investigated using high-resolution electron energy-loss spectroscopy in transmission. The intercalation is fully reversible and causes an expansion of the intertube distance in the nanotube bundles similar to that in a Cs-doped nanotube. The analysis of the core-level excitations shows that, in contrast to the alkali-metal intercalated nanotubes, there is hybridization between nanotube and barium states and the barium intercalation gives rise to a perturbation of the nanotube electronic states above the Fermi level. As a consequence of hybridization and charge transfer the formation of a free charge carrier plasmon is observed. In the case of the highest doping, the unscreened plasmon energy is about two times higher than that of the fully alkali-metal-doped nanotubes.

Figure 1

The evolution of the electron diffraction pattern of SWCNT’s with increasing Ba concentration from top (pristine one) to bottom (full doping).

Figure 2

The dependence of the nearest intertube distance on the relative Ba concentration (●) given by the % value of the maximum doping as explained in detail in the text, as compared with Cs-doped SWCNT’s (엯).

Figure 3

The evolution of the C $1s$ spectra (left panel) and Ba $3d$ (right panel) spectra with increasing Ba contents from the bottom (pristine SWCNT’s) to the top (fully doped SWCNT’s), as indicated by the % values of maximum doping.

Figure 4

C $1s$ core-level spectra of the pristine SWCNT’s (curve $E$), the fully Ba-doped (curve $C$), and fully Ba deintercalated (curve $D$) SWCNT’s. For comparison, the spectra of GIC $\mathrm{K}{\mathrm{C}}_8$ (curve $B$) and fully K-doped SWCNT’s (curve $A$) are also shown. The spilt ${\pi }^{\star }$ peak of the Ba-doped SWCNT’s is indicated by arrows.

Figure 5

The evolution of the loss function with increasing Ba concentrations (as indicated by the numbers) from the top (pristine) to the bottom (fully doped SWCNT’s) at $q=0.15{\mathrm{\AA }}^{-1}$. The dashed arrow and line indicate the shift of $\pi +\sigma$ plasmon with doping.

Figure 6

Comparison between the measured loss function (open circles) and the fitting results (solid lines) for the doped SWCNT’s with different Ba concents.