Electronic structure of surface compounds formed under thermal annealing of the La graphite interface

Surface compounds grown by step-by-step thermal annealing of the La/graphit e interface in a temperature range from 600 K to 1400 K were studied by ang le-resolved valence-band photoemission (PE), resonant and C 1s core-level P E as well as by C(KW) Auger electron spectroscopy and low-energy electron d iffraction. It was found that annealing of the system at temperatures betwe en 600 K and 1000 K leads to formation of an ordered La carbide phase with non-dispersive valence-band electronic structure. High-temperature annealin g up to 1100-1400 K results in formation of a thin layer of intercalation-l ike compound on top of the carbide phase. Valence-band energy distribution curves taken for this system reveal (i) graphite-like dispersion of electro nic states shifted toward higher binding energies compared with their posit ion in pristine graphite and (ii) a series of carbide-derived features seen through the thin film of intercalation-like compound. C 1s PE spectra meas ured for the high-temperature phase have two-component lineshape in accorda nce with the layered structure of the system. (C) 1999 Elsevier Science B.V . All rights reserved.