Structural change of single-walled carbon nanotube induced by soft X-ray irradiation

Single-walled carbon nanotubes (SWNTs) grown on Si(1 0 0) were irradiated with X-ray having the spectrum with a peak at 277 eV. We measured Raman scattering spectra of the samples before and after the irradiation at various fluences and found that the relative intensity of the defect-related band, D band, to the band of the tangential shear modes of the carbon atoms in a graphene sheet, G band, was enhanced by the irradiation. The fluence dependence of this intensity ratio, D/G  , took a peak around the fluence of 7×1013cm-2. Further X-ray irradiation reduced the D/G to around half of the maximum. Detail inspection of the low frequency Raman spectra revealed that the radial breathing modes of the SWNTs were modified by the irradiation. The result suggests that the X-ray irradiation gives rise to not only defect formation but also modification of the SWNT structure.