Photoemission study of K on graphite

The physical and electronic structure of the dispersed and $(2\mathrm{}\times 2)$ 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 $0.4\hspace{0.5em}\mathrm{eV}$ 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 $(2\mathrm{}\times 2)$ 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).