Surface Phonon Dispersion in Graphite and its Modification Under Interaction with Lanthanum

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Abstract
Using high resolution electron energy loss spectroscopy (HREELS) the surface phonon dispersion of graphite has been determined in the Γ K direction over the whole energy range and the whole Brillouin zone. By depositing lanthanum and annealing we prepared a GIC-like phase which grows on top of an intermediate carbide. The phonon dispersion of this phase shows the same modes as graphite, but the optical ones are softened and the acoustical ones are stiffened. This is described within a Born-von Karman model. The evolution of the phonon dispersion gives a first hint that the GIC-like phase may develop in two stages: first a monolayer graphite on top of the carbide and then the very thin GIC layer.