The BWF signal appears only when the electronic density of states at the Fermi energy has a finite value Returning to , in their review we can find told that the Raman G band in the multiwall carbon nanotubes, MWNTs, change. "Because of the large diameter of the outer tubes for typical multi-wall carbon nanotubes (MWNTs) and because MWNTs contain an ensemble of carbon nanotubes with diameters ranging from small to very large, most of the characteristic differences that distinguish the Raman spectra in SWNTs from the spectra for graphite are not so evident in MWNTs. … the G + -G - splitting is large for small diameter SWNT tubes, the corresponding splitting of the G band in MWNTs is both small in intensity and smeared out due to the effect of the diameter distribution within the individual MWNTs, and because of the variation between different tubes in an ensemble of MWNTs in typical experimental samples. Therefore the G-band feature predominantly exhibits a weakly asymmetric characteristic lineshape, with a peak appearing close to the graphite frequency of 1582 cm -1 " . That is, in MWNT we observe an asymmetric G band.