Electronic properties of ${\mathrm{FeCl}}_3$-intercalated single-wall carbon nanotubes

The electronic properties of ${\mathrm{FeCl}}_3$ intercalated single-wall carbon nanotubes were investigated using high-resolution electron energy-loss spectroscopy in transmission and optical spectroscopy. The lowering of the nanotube Fermi level is directly measured via electronic excitations from C $1s$ to empty carbon $2p$ states derived from the doping. The charge induced disappearance of the optically allowed transitions is demonstrated by the evolution of the optical absorption spectrum. In the loss function the appearance of a new feature can be assigned to plasmon excitations. The optical properties of ${\mathrm{FeCl}}_3$ intercalated nanotubes are comparable with those of fully potassium doped nanotubes. Upon annealing, the intercalant can be removed reversibly.

Figure 1

The electron diffraction pattern of SWCNT’s with ${\mathrm{FeCl}}_3$ doping (bottom), the stars label the features arising with ${\mathrm{FeCl}}_3$ intercalation. For comparison, the spectra of the pristine nanotube (middle) and the de-intercalated one (top) are also shown.

Figure 2

C $1s$ core-level excitations of pristine (dashed line) and ${\mathrm{FeCl}}_3$-doped SWCNT’s (solid line). The arrow indicates the additional empty states due to doping. The inset shows the difference between the spectral weight of doped and pristine nanotubes after normalizing the two spectra at the ${\pi }^{\star }$ states (Ref. 28).

Figure 3

The evolution of the optical absorption spectrum with increasing ${\mathrm{FeCl}}_3$ doping. From top to bottom the doping level increases. The arrow in the bottom spectrum indicates the doping-induced optical peak. Dashed arrow points out the plasmon energy.

Figure 4

Comparison of the loss function of fully ${\mathrm{FeCl}}_3$-doped SWCNT’s (bottom) with de-intercalated (middle) and pristine SWCNT’s (top) at a momentum transfer $q=0.15{\mathrm{\AA }}^{-1}$. The inset shows the fitting analysis (solid line) of the Drude plasmon in the loss function of the doped sample (open circle).