J. Barth

Surface shifts on rare earth metals

Abstract Surface shifts on various rare earth metals are determined using high resolution synchrotron radiation induced photoelectron spectroscopy. The mean free path of the photoelectrons is evaluated. The surface of Sm metal is confirmed to be completely divalent.

4f-surface binding energy shift for Eu and Gd metals

Abstract Synchrotron radiation excited photoemission spectra of Eu and Gd are presented. For Eu a 4 f -surface component is resolved with 0.63 eV binding energy shift. For Gd the comparison with XPS data gives strong evidence for a surface shifted 4 f -component ( ΔE =0.48 eV). The mean free path of photoelectrons is determined.

Photoemission investigation of hexagonal BN: Band structure and atomic effects

Abstract Photoemission valence band spectra and the polarization dependent photoyield at the B K -edge are compared to calculated densities of states. Excitonic effects at the edge are discussed. For the decay of exciton and ionized core the influence of atomic effects is shown.

Surface photoemission in the 4d band from polycrystalline silver surfaces

Abstract Surface induced local d-band states in the upper 4d band between ∼ 4 and ∼ 5.2 eV below EFermi have been identified for polycrystalline silver films in photoemission experiments using synchroton radiation. A thin over-coat (10 a) by an Al film leads to a depression of these surface induced local states whereas a change from s- to p-polarized excitation leads to an enhancement. Deposition of additional silver (∼ 3 A) at 120 K induces additional emission 4.2 eV below EF with a FWHM of only ∼ 0.4 eV.

Determination of partial subshell cross-sections and electron mean free path in solids with the photoemission set-up at the FLIPPER monochromator

Abstract The methods of quantitative measurements of photoemission intensities on solids are outlined for experiments using monochromatized synchrotron radiation as a tunable light source. Results are explicitely calculated for the photoemission set-up at the FLIPPER monochromator which covers the energy range between 20 eV and 500 eV. A procedure is given to determine the transmission of an electron analyzer in the retarding mode.

Chemically shifted surface core-levels and surface segregation in EuAu and YbAu alloys

Abstract Chemically shifted surface core-level binding energies are observed for the rare-earth alloy component in Eu1−xAux and Yb1−xAux. Furthermore, these shifts are different from the chemical shifts of the bulk 4f levels. The surface core-levels are used to identify surface segregation of the lanthanide metal in the present alloys.

A study of Al/Si(111)-cleaved interface by photoemission, Auger electron yield, and Auger electron spectroscopies

Abstract Photoemission, Auger electron yield, and Auger electron spectra are observed for Al/Si(111)-cleaved interfaces. The Al 3 p derived state which becomes metallic at monolayer coverage is introduced near the top of the valence band. The Fermi level is stabilized in this metallic state. The present result favors the on-top geometry of Al atoms on a Si(111)-cleaved surface.

Two valence states in oxidized europium metal

Abstract Evaporated Eu films were exposed to oxygen up to 100 L. Using novel techniques of photoelectron spectroscopy in connection with synchrotron radiation as a tunable light source we detect the presence of both Eu 2+ and Eu 3+ ions in the sample with a close correspondence to mixed-valence Eu 3 O 4 . At elevated temperature (400°C) only Eu 2+ is found.

Observation of resonance recombination lines in electron excited auger spectra of Gd

Abstract Combined measurements of electron excited N 4,5 Auger spectra and photoelectron emission on clean and oxidized Gd lead to a distinction between Auger lines originating from 4 d → continuum and 4 d → 4ƒ resonance excitations. Several Auger structures are identified as due to the direct recombination of 4 d 9 4ƒ 8 states with the 4 f and valence electrons. The shape of the most prominent Auger line for oxidized Gd agrees perfectly with the Fano profile of the 4ƒ photoemission intensity.