Resonance Raman spectroscopy in Si and C ion-implanted double-wall carbon nanotubes

Abstract

The effect of 170 keV Si and 100 keV C ion bombardment on the structure and properties of highly pure, double-wall carbon nanotubes has been investigated using resonance Raman spectroscopy. The implantations were performed at room temperature with ion doses ranging between 1×1013 ions/cm2 and 1×1015 ions/cm2. As expected, the Si irradiation created more disorder than the C irradiation for the same ion fluence. For both species, as the ion-implantation fluence increased, the D-band intensity increased, while the G-band intensity decreased, indicating increased lattice disorder, in analogous form to other forms of graphite and other nanotube types. The frequency of the G band decreased with increasing dose, reflecting a softening of the phonon mode due to lattice defects. With increasing ion fluence, the radial breathing modes (RBMs) of the outer tubes (either semiconducting or metallic) disappeared before the respective RBM bands from the inner tubes, suggesting that the outer nanotubes are more affected than the inner nanotubes by the ion irradiation. After Si ion bombardment to a dose of 1×1015 ions/cm2, the Raman spectrum resembled that of highly disordered graphite, indicating that the lattice structures of the inner and outer nanotubes were almost completely destroyed. However, laser annealing partially restored the crystalline structure of the nanotubes, as evidenced by the re-emergence of the G and RBM bands and the significant attenuation of the D band in the Raman spectrum.