Spectroscopic evidence on weak electron transfer from intercalated iodine molecules to single-walled carbon nanotubes

The chemical bonding character of iodine-intercalated single-walled carbon nanotube (I-SWNT) has been systematically investigated with combinative X-ray spectroscopies. According to I L-I-edge X-ray absorption near-edge structure (XANES) analysis, a white line peak corresponding to 2s -> 5p transition shows nearly identical but slightly stronger intensity for the I-SWNT than for neutral iodine, indicative of a weak electron transfer from intercalated iodine to SWNT. In contrast, there are remarkable spectral differences in the I L-I-edge XANES spectra of I-SWNT and iodine-intercalated Bi2Sr2CaCu2Oy. This allows us to rule out the possibility of negatively charged polyiodide ions in the present I-SWNT sample prepared by vapor-phase reaction. Also, we have found that a contact between iodine and SWNT during the synthesis has negligible influence on the chemical bonding nature of intercalated iodine species. The electron transfer from iodine to SWNT is further supported by C 1s X-ray photoelectron spectroscopy revealing the reduction of carbon in SWNT upon iodine intercalation.