Photoemission study of K on graphite

The physical and electronic structure of the dispersed and (2×2) phases of K/graphite have been characterized by valence and core-level photoemission. Charge transfer from K to graphite is found to occur at all coverages, and includes transfer of charge to the second graphite layer. A rigid band description is reasonably successful in describing important aspects of the data, and our results are consistent with a shift of approximately 0.4 eV in the surface graphite layer for both phases. The C 1s line shape and binding-energy shift as a function of charge transfer can be understood qualitatively by taking into account rigid band effects and the effects of a core hole on the density of states. For the (2×2) phase the metallic overlayer contributes extrinsic satellites to the C 1s line shape. The K 3p spectrum is strongly affected by the overlayer phase, and in addition indicates very little variation in the substrate charge distribution as a function of coverage in the dispersed phase. The lack of an interface K 3p binding-energy shift for a K bilayer or multilayer is ascribed to a weak K-graphite bond for metallic overlayers. The results have implications for the interpretation of photoelectron spectra of alkali graphite intercalation compounds (GIC’s).