Absorption spectroscopy of single-wall carbon nanotubes: effects of chemical and electrochemical doping

Changes in electronic states of single-wall carbon nanotubes (SWNT) induced by chemical and electrochemical doping were investigated by optical absorption spectroscopy in the range from the visible to near infrared. When SWNT was doped with a bulky organic electron acceptor, decrease of the absorption peaks similar to that previously found for halogen doping was observed but with a relatively slower rate of decrease, reflecting different diffusion dynamics of the dopants as well as the morphology of the SWNT film. Electrochemical doping induced by the continuous shift of the electrode potential caused sequential decrease of three absorption peaks, which was explained by the sequential removal of electrons from three occupied bands in the semiconducting and metallic phase of SWNT. Implications of these results are discussed in relation to the elucidation of electronic properties of SWNT.