Structural determination of iodine localization in single-walled carbon nanotube bundles by diffraction methods

X-ray- and neutron-diffraction investigations of iodine intercalated single-walled carbon nanotubes are reported. Charge transfer between nanotubes and iodine leads to the formation of I-n(-) species (mainly I-3(-) and I-5(-)) as shown by Raman spectroscopy. By combining x-ray and neutron experiments, we show that the I-n(-) species are mainly localized inside the tubes. By comparing the experimental diagrams to our calculations, we show that some I-n(-) species are also present in the channels in between three tubes inside the bundles. The intercalation process also increases the disorder of the two-dimensional triangular lattice leading to a broad distribution of the iodine-carbon distances. Well ordered single-walled nanotube bundles are recovered after dedoping.