Densities of unoccupied states in HOPG, C6Li and C8K studied by photoyield and Bremsstrahlung isochromat spectroscopy

Abstract The two techniques employed for studying the empty conduction band states in stage-1 graphite intercalation compounds (here C 6 Li and C 8 K) provide complementary information. The photoyield experiments give the local (site decomposed) densities of unoccupied states and probe, in particular, the C π ∗ band and the Li(2p) and K(3d)/(4s) states. The high energy Bremsstrahlung isochromat spectroscopy (BIS) data appear to enhance transitions to the C σ ∗ bands. The photoyield experiments show clearly the presence of C π ∗ states at E F but indicate negligible contributions to the densities of states at E F from Li(2p) states and K(3d) states. The shift of E F into the conduction band is not completely rigid band-like, but the main features are observed ∼1 eV closer to E F in C 8 K and ∼2 eV closer in C 6 Li. The strong dependence of the intensity of observed peaks on the excitation polarization direction should contribute to the identification of their band origins if such effects are taken into account in band structure calculations.