antibonding conduction bands of the swnt the average c u2014 c bond strength is weakened resulting in a downshift or softening of the vibrational frequency the reason for the upshift that occurs upon p doping is less obvious one would intuitively expect that removing electron density from the fully occupied bonding valence band of a swnt would weaken the c u2014 c bonding resulting in a downshift in the g band frequency this was not in fact what was observed one explanation for this behaviour is that the addition of some sp 3 character to the sp 2 hybridized orbitals which results from the curvature of the graphitic structure required to form a tube results in coulomb repulsion particularly in small diameter tubes removing electron density from these orbitals reduces the repulsion resulting in stronger net bonding and a higher g band frequency based on these considerations if the swnts were to lose charge to the polymer matrix one would expect an upshift in the g band and conversely a downshift is expected if charge is gained from the matrix fig2 a shows the measured raman spectra of the laser ablated tubes before and after dispersion in the u03b2 cn apb odpa matrix at a concentration of 0 5.