Lattice dynamics of CaC6 by Raman spectroscopy

Phonon modes in the first-stage intercalation compound CaC6 were studied by the backward micro-Raman scattering technique. Although the cleaved surface was rather unstable, spectra from virgin surfaces systematically show two bands in the frequency range where first-order Raman scattering is expected. By comparison with published first-principles calculations, these bands are assigned to Raman-active E-g modes corresponding to the in-plane bond-stretching mode (band near 1500 cm(-1)) and to the out-of-plane puckering mode (band near 450 cm(-1)) of the graphene layer. Considerable linewidth of the stretching mode (full width at half maximum about 100 cm(-1)) might be partly caused by the electron-phonon interaction.