Soft X-ray absorption spectroscopy study of chemical states, orientation, and oxygen content of ion-irradiated vertically aligned multiwalled carbon nanotubes

Low-energy Ar ions (0.5-2 keV) were irradiated onto vertically aligned multiwalled carbon nanotube (VA-MWCNT) films, and the chemical states, orientation, and oxygen content of the irradiated VA-MWCNT films were investigated by soft X-ray absorption spectroscopy (XAS). After irradiation, two additional peaks appeared in the XAS spectra in the C K region, indicating a significant change in the electronic structure. Furthermore, it was found that the VA-MWCNT films were oxidized after irradiation. The results of chemical-state analyses of the XAS spectra in both the C K and O K regions indicated the formation of carboxyl groups (COOH) on the surface of the VA-MWCNT films upon irradiation. The oxygen content of the VA-MWCNT films increased with increasing ion energy and fluence.