Charge transfer and Fermi level shift inp-doped single-walled carbon nanotubes

The electronic properties of $p$-doped single-walled carbon nanotube (SWNT) bulk samples were studied by temperature-dependent resistivity and thermopower, optical reflectivity, and Raman spectroscopy. These all give consistent results for the Fermi level downshift $\left(\Delta E_F\right)$ induced by doping. We find $\Delta E_F\approx 0.35\mathrm{eV}$ and $0.50\mathrm{eV}$ for concentrated nitric and sulfuric acid doping respectively. With these values, the evolution of Raman spectra can be explained by variations in the resonance condition as $E_F$ moves down into the valence band. Furthermore, we find no evidence for diameter-selective doping, nor any distinction between doping responses of metallic and semiconducting tubes.