Raman scattering from in-plane lattice modes in low-stage graphite-alkali-metal compounds

Low-temperature Raman scattering results for stage 1, 2, and 3 graphite-alkali-metal intercalation compounds are reported for in-plane modes using the Brewster-angle back-scattering geometry. Detailed full spectra are presented for stage 1, 2, and 3 compounds of graphite-Rb at 77 K. Particular attention is given to the structure which occurs at $\gtrsim 560$ ${\mathrm{cm}}^{-1\mathrm{}}$ in the stage-1 compounds ${\mathrm{C}}_8$K, ${\mathrm{C}}_8$Rb, ${\mathrm{C}}_8$Cs. This structure is shown to have two components of different symmetries and is related to the zone-edge $M_{1g}$ phonon mode of pristine graphite.