Diffusion and implantation of dopants in single-wall carbon nanotubes:a spectroscopic investigation of chemical and electronic properties

Raman measurements, performed on MWCNTs grown by arc discharge method in He atmosphere, have pointed out the occurrence of a band at 1780- 1860 cm–1, regardless of the use of a catalytic Ni-Cr alloy in the synthesis process [127]. This band has been attributed to the presence of carbon linear chains inside the innermost tube. The maximum Raman signal from the chain-related L bands is found inside a circular region, in correspondence with enhanced secondary electron emission, as evidenced by a strong white color in the SEM images. Furthermore, a temperature-dependent Raman study, up to about 1000K, has revealed for the first time a phase transition trend [128], which seems to be related to a strong, reversible reduction of the Peierls distortion at high temperatures.