Synthesis of heterostructured SiC and C-SiC nanotubes by ion irradiation-induced changes in crystallinity

Amorphous SiC nanotubes are successfully synthesized for the first time by the irradiation of polycrystalline SiC nanotubes with 340 keV Si+ ions. A polycrystalline/amorphous heterostructured SiC nanotube, in which polycrystalline SiC and amorphous SiC coexist in the same nanotube, is also synthesized by ion irradiation with a mask in front of the polycrystalline SiC nanotube. According to evaluation by electron energy loss spectroscopy, the plasmon energies of the SiC nanotube change rapidly at the interface between the polycrystalline and amorphous regions. The volume swelling induced by amorphization, as evaluated from the differences in plasmon energies, is approximately 5.0%. This result reveals that more relaxed amorphous SiC nanotubes with higher densities can be produced. The graphitic shells in the carbon layer of C-SiC nanotubes are found to gradually bend to align with the radial directions of the nanotubes by ion irradiation. Since graphite (002) spots in the selected-area electron diffraction pattern are clearly observed even after ion irradiation, the carbon layer in the C-SiC nanotube maintains crystallinity. Moreover, a new multi-walled carbon nanotube with graphitic shells completely parallel to the radial direction of the nanotube is also produced inside the amorphous SiC tubular layer, in the case of large-caliber C-SiC nanotubes.