SURFACE ELECTRONIC-STRUCTURE OF EPITAXIAL CE AND LA FILMS

We report on a detailed photoemission (PE) study of monocrystalline Ce and La metal films grown on W(110). Angle-resolved PE reveals that bo th systems have very similar valence-band structures, with the observe d dispersions being in good agreement with local-density approximation band-structure calculations. These calculations were performed for th ree different close-packed crystal structures of La and Ce metal, givi ng evidence for a double hcp structure of the films, i.e., a beta phas e in the case of Ce. The pronounced surface state, characteristic for the close-packed surfaces of trivalent lanthanide metals, is shown to exist also for beta-Ce(0001), extending over a wide range of the surfa ce Brillouin zone. The 4f electronic structure of the Ce film was stud ied by resonant PE at the 4d --> 4f threshold. A separation of bulk an d surface contributions with high resolution was achieved by quenching the surface signal with a Dy overlayer. In this way, a surface shift of (140 +/- 40) meV of the 4f(0) final state emission was found for be ta-Ce, which is discussed in connection with f - d hybridization.