Raman scattering of single-walled carbon nanotubes implanted with ultra-low-energy oxygen ions

Single-walled carbon nanotubes (SWNTs) implanted with ultra-low-energy oxygen (O(+)) ions have been studied by means of Raman scattering experiments. The relative intensities of the D-band related to some defects increase with the O(+) dose in the Raman spectra of the implanted samples. Although no recognizable shift of phonon energies due to the ion implantation has been observed, the intensities of the Stokes and anti-Stokes lines originated from radial breathing modes of SWNTs which exhibit various behaviors due to degree of the implantation, indicating that the resonant energies are changed. To explain these findings, the structure and the electronic states of SWNTs with substitutional O impurities have been studied by applying theoretical calculations based on the first principle method and a tight-binding method. As a result, it has been suggested that the incorporation of oxygen atoms at carbon sites is plausible, and the experimental observation can thus be consistently explained on the basis of the O impurities in SWNTs.