C 1s NEXAFS study of rare-earth's (La, Eu)-graphite intercalation compounds

Electronic structure of unoccupied states of Eu- and thin surface layer of La-intercalation compounds was studied by light polarization dependent NEXA FS at the C Is threshold in a bulk sensitive (E-kin=1-2 eV) and a more surf ace sensitive (E-kin=265 eV) partial electron yield mode. It was shown that the C Is spectra in both cases are mainly characterized by the pi*- and si gma*-symmetry graphite-derived features. For both systems the pi*-derived p eak was found at similar energies of exciting photons as for pristine graph ite. A decrease of relative intensity of the pi*-originated structure in in tercalation compounds can be understood by partial occupation of the pi*-de rived states upon intercalation due to a charge transfer from rare-earth (R E) atoms. NEXAFS features found on both sides of the pi* response may be re lated to pd hybrids forming as a result of chemical interaction between RE atoms and graphite layers. (C) 1999 Elsevier Science B.V. All rights reserv ed.