Transition from one-dimensional to three-dimensional behavior induced by lithium doping in single wall carbon nanotubes

The electronic properties of Li doped single-wall carbon nanotubes were studied by high-resolution photoemission spectroscopy. Upon Li intercalation, the limited displacement of the Fermi level agrees with a partial charge transfer of the Li2s electron to the $\mathrm{C}2p\text{−}{\pi }^{*}$ states. The increase of the density of states near the Fermi level with Li concentration suggests a transition from the one-dimensional Tomonaga-Luttinger liquid behavior, observed in the pristine nanotubes, to three-dimensional transport properties in the doped sample. The increased spectral weight near the Fermi level can be also partly ascribed to the formation of new states in the conduction band due to the hybridization between Li and C.

Figure 1

Lils spectra measured on the Li doped SWNTs. The peak intensities were rescaled in order to optimize the comparison of the spectral profiles. For the highest Li dose, a Li multilayer condenses on the sample. In this case the $\mathrm{Li}∕\mathrm{C}$ ratio reported on the right was calculated considering only the concentration of the ionized lithium.

Figure 2

a) C1s experimental spectra (dots) and best fit curves (lines) taken on the pristine and lithiated SWNTs at increasing Li doping level. The peak intensities were normalized to the same height. The inset shows the BE shift measured for the C1s peak and the $2p\text{−}\pi$ band vs the $\mathrm{Li}∕\mathrm{C}$ ratio.

Figure 3

Photoemission spectra measured on pristine and Li doped SWNTs. The dashed lines are guidelines for the evolution of the VHS peaks. The left inset shows the evolution of the near-Fermi-level region with increasing Li doping. The increase of the spectra integral between $-0.2$ and $0.2\mathrm{eV}$ with respect to the pristine SWNTs is shown as a function of the $\mathrm{Li}∕\mathrm{C}$ ratio in the inset on the right side.

Figure 4

Log-log representation of the photoemission spectra measured near the Fermi energy on pristine and Li doped SWNTs. The fits up to $0.2\mathrm{eV}$ provide the $\alpha$ values plotted vs the $\mathrm{Li}∕\mathrm{C}$ ratio in the bottom inset. The bottom inset also displays the best fit curve (solid) for the $\alpha$ values, obtained with a power-law decay function (dots) plus a Gaussian distribution (dashes). In the top inset the valence band shapes measured on pristine (rescaled) and doped $(\mathrm{Li}∕\mathrm{C}=0.05)$ SWNTs are compared.