Abstract
IR and EPR spectroscopic investigations of redox- p-doped semiconducting (6,5) single-wall carbon nanotubes (s-SWNTs) were used to study carrier localization and delocalization from low- up to degenerate doping levels. At low carrier concentrations, the analysis of IR-intraband transitions as well as the appearance of a doping-induced vibrational D-band anti-resonance, point to charge-localization on the few nm length-scale. Moreover, the rise of a spin 1/2 signal in EPR closely tracks the increase of the doping level, supporting the notion of charge-localization at low carrier concentrations. At doping levels exceeding 0.1 nm-1, EPR data as well as intra- and D-band absorption in the IR point to antiferromagnetic coupling between surplus charge carriers becoming dominant. These results are expected to be relevant for field- or redox-chemical doping of s-SWNTs in any polarizable, heterogeneous environment.