Raman scattering inC60and alkali-metal-dopedC60films

Abstract

The Raman-active modes of solid films of ${\mathrm{C}}_{60}$ and ${\mathit{M}}_{\mathit{X}}$ ${\mathrm{C}}_{60}$ (x∼6; M=K, Rb, Cs) have been studied experimentally. The mode activity is dominated by intraball interactions, and the effect of the ${\mathit{M}}^{+}$ ions on the ${\mathrm{C}}_{60}$ spectrum is observed to be almost insensitive to the radius or mass of the alkali metal. Tangential modes of solid ${\mathrm{C}}_{60}$ are observed to soften in ${\mathit{M}}_6$ ${\mathrm{C}}_{60}$ by ∼60 ${\mathrm{cm}}^{\mathrm{-}1}$, which can be attributed to a charge-transfer-induced elongation of the intraball bond lengths, similar to that observed in graphite intercalation compounds. Conversely, the radial modes are found to upshift slightly, indicating that a competing mechanism counteracts the effect of the bond elongation.