Surface phonon dispersion of a graphite monolayer adsorbed on Ni(111) and its modification caused by intercalation of Yb, La and Cu layers

Abstract

The surface phonon dispersion of a monolayer of graphite (MG) on Ni(111) has been measured in the Γ̄K̄ direction of the Brillouin zone over the whole energy range using high resolution electron energy loss spectroscopy. The MG/Ni(111) system is characterized by graphite-like phonon modes softened due to the interaction of MG with the substrate. The splitting of the ZA and ZO modes at the K̄ point previously reported for the surface phonon dispersion of graphite is even more pronounced on MG/Ni(111). We have successfully intercalated Yb and Cu underneath the monolayer graphite by deposition of these metals at room temperature and subsequent heating to 400–500 and 400°C, respectively. The phonon dispersion relations obtained after intercalation of Yb are very similar to those of the MG/Ni(111) system, as expected from the strong interaction between MG and the underlying Yb atoms. In the case of MG/Cu/Ni(111), in contrast, the corresponding surface phonon dispersion curves are very similar to those of graphite. Measurements of C KVV Auger spectra for this system demonstrate that the observed stiffening is caused by the smaller charge transfer from the intercalated copper atoms into the π-states of graphite. Deposition of La onto MG/Ni(111) with subsequent annealing leads to the formation of graphite islands ontop of the thin surface carbide film.