Chemical states of electrochemically doped single wall carbon nanotubes as probed by Raman spectroelectrochemistry and ex situ X-ray photoelectron spectroscopy

X-ray photoclectron spectroscopy (XPS) was combined with Raman spectroelectrochemistry to study the electrochemically doped states of single wall carbon nanotube (SWCNT) bundles. The ex situ measurements indicated a significant drop of doping level as compared to in situ measurements. However, after this initial decrease of the doping level, the electronic structure of SWCNT bundles was found to be stable. The XPS elemental analysis indicated that electrolyte ions penetrate into the nanotube bundles. Furthermore, for the n-doped (electrochemically reduced) sample, an increase of the relative surface concentration of different C-O groups was observed, which was caused by electrochemical reduction Of ClO4- ions. Comparison of the ex situ Raman and XP spectra showed that an electrode potential shift of I V corresponds to the Fermi level shift of ca. 0.5 eV.