Charge transfer and Fermi level shift in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-doped single-walled carbon nanotubes

Abstract

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 $(\ensuremath{\Delta}{E}_{F})$ induced by doping. We find $\ensuremath{\Delta}{E}_{F}\ensuremath{\approx}0.35\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and $0.50\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ 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.