The two peaks G′ band in carbon nanotubes

In this work we discuss the nature of the extra peak that appears in the low frequency side the G′ band in the Raman spectra of single wall and double wall carbon nanotubes. This peak has been reported in many articles assigned as either the G′ band from small diameter nanotubes or the response for fulfilment of resonance conditions with incident and scattered light. Here we show that this peak is present in the Raman spectra independently on the diameter distribution of the sample and disappears after heat treatment. We believe the lower frequency component of the two-peaks G′ band in carbon nanotubes is related to the presence of defects in the carbon nanotube structure.