Tumbling atoms and evidence for charge transfer in La2@C80@SWNT

Using transmission electron microscopy, we demonstrate the insertion of the metallofullerene La2@C80 into 1.4 nm diameter single wall carbon nanotubes. Micrographs indicate that the spheroidal D2h isomer having an IhC80 cage ∼0.8 nm in diameter is preferred. For the first time, endohedral atoms inside a metallofullerene are directly imaged. The La atoms are seen to undergo a discontinuous tumbling motion inside their C80 cage. The measured La–La separation is slightly larger than is predicted by theory. These data suggest that interactions between the nanotube and La2@C80 have changed the molecules' behaviors. Our results prove that extrinsic molecular species can be introduced into carbon nanotubes.