Multi-wavelength Raman scattering spectroscopic study of X-ray-irradiated single-walled carbon nanotube: Possibility of irradiation-induced electronic structure change

The resonant Raman scattering spectra of X-ray-irradiated single-walled carbon nanotubes (SWNTs) have been measured at 532, 561, 568, 647, and 660 nm. We found that X-ray irradiation induced a marked change in the radial breathing mode (RBM). In order to analyze the X-ray-induced change in the RBM spectra, we drew a map of the RBM peaks showing the relation between the peak position and the probe beam energy by interpolating the spectra measured at the probe wavelengths. We found that shifting the transition energy by 0.05 eV reproduced the RBM spectra of the irradiated SWNTs. This model well explains the results of our optical absorption measurements and previous reports on theoretical and scanning tunneling microscopy studies by other groups. On the basis of these results, we suggest that X-ray irradiation is one of the practical methods of controlling the electronic properties of SWNTs.