Valence- and core-electronic excitations in potassium-intercalated graphite

The valence- and core-electronic excitations of states 1 - 3 potassium-intercalated graphite have been measured with high-resolution (0.1 eV) electron-energy-loss spectroscopy. Contrary to previous measurements, strong dispersion was observed for intraband plasmons. In addition, the momentum dependence of the spectrum of single-particle intraband excitations was measured for the first time in these materials. Kramers-Kronig analysis of energy-loss spectra yielded the dielectric functions for KC₈ and KC₂₄. Interband transitions at the M point of pristine graphite which occur at 4.3 eV are essentially unchanged in KC₂₄ but are shifted to 4.0 eV in KC₈. The threshold for interband graphite excitations yields estimates of the Fermi-level shift relative to pristine graphite of 1.4 eV for KC₈ and 1.05 eV for KC₂₄. The spectra of potassium $3p$ excitations suggest that the valence charge density screening the potassium atoms decreases with increasing stage. The spectra of carbon $1s$ core-electron excitations show positive evidence of the hybridization of carbon and potassium wave functions near the Fermi level in KC₈.