Infrared spectroscopic study of O2 interaction with carbon nanotubes.

Infrared reflection-absorption spectroscopic measurements have been performed on single-wall carbon nanotubes (SWNTs), cleaned by heating to approximately 500 degrees C in vacuo, during exposure to pure 16O2 or 18O2 at room temperature and at pressures of up to approximately 630 Torr. No vibrational signature of any form of adsorbed O is detected. However, structure is seen which is very similar to that observed for the adsorption of atomic H or D and which indicates changes in the SWNT vibrational spectrum. The close similarity between the spectra for atomic H and D, on one hand, and O2 on the other is an unexpected result. Changes are also noted in the broad background extending throughout the mid-IR which arises from the Drude contribution to the reflectance. All these effects increase with O2 exposure and are essentially irreversible upon evacuation of the gas. The results are consistent with other data indicating that O2 interacts only weakly with, and does not chemisorb on, pristine regions of the SWNT under these conditions. The small and irreversible effects seen upon O2 exposure are interpreted in terms of enhanced chemisorption, at or near defective regions of the SWNT wall, which saturates at a low O coverage.