Specific Raman signatures of a dimetallofullerene peapod.

We report on the Raman spectroscopy of a dimetallofullerene peapod, (La(2)@C(80))(m)@SWNT. Drastic changes are observed with respect to pristine nanotubes. A sharp intense line at 142 cm(-1) is interpreted as a signature of polymerization of the encapsulated metallofullerenes. Additional strong signatures appear at about 400, 520, and 640 cm(-1), respectively. Their intensity suggests the existence of an enhancement effect. The stiffening and the up-shift of the G-band modes appear to imply that a charge transfer process between the nanotube and the peas occurs.