| AVS 59th Annual International Symposium and Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+TF+SS+MI-MoA |
| Session: | Actinides and Rare Earths: Thin Films and Surface Science |
| Presenter: | F. Offi, CNISM and Univ. Roma Tre, Italy |
| Authors: | F. Offi, CNISM and Univ. Roma Tre, Italy P. Vilmercati, ELETTRA Sincrotrone Trieste, Italy L. Petaccia, ELETTRA Sincrotrone Trieste, Italy S. Gorovikov, ELETTRA Sincrotrone Trieste, Italy A. Ruocco, CNISM and Univ. Roma Tre, Italy M.I. Trioni, CNR-ISTM, Milano, Italy A. Rizzo, CNISM and Univ. Roma Tre, Italy A. Goldoni, ELETTRA Sincrotrone Trieste, Italy G. Stefani, CNISM and Univ. Roma Tre, Italy G. Panaccione, CNR-IOM, Basovizza-Trieste, Italy S. Iacobucci, CNI-IFN, Rome, Italy |
| Correspondent: | Click to Email |
The peculiar electronic structure of rare-earth elements and compounds is mostly defined by the partially filled 4f band. Of particular interest is the investigation of the valence states, which is linked to the degree of hybridization of f electrons with delocalized s-d bands. In the simple case of Yb, the 4f states are fully occupied with a Fermi level of 6s character and a 2+ valency. However, the occupation of the Yb valence band has been the subject of several investigations over the years, intended in particular to separate the contribution of 5d states. Early experimental photoelectron emission (PES) spectra at very low excitation energy (hν < 10 eV) have reported a spectral modulation in the region close to the Fermi level that was attributed to the emission from a 5d band. The poor energy resolution did not allow however a detailed investigation of such spectral features. In recent years this low energy photoemission spectroscopy (LEPES) encountered a renewed interest, under the stimulus of the extremely high energy resolution obtainable with laser excited LEPES and given the expectation of a large increase of the bulk sensitivity at these low energies. W e monitored the 4f spectral intensity in polycrystalline Yb films in the LEPES regime ( between 5.5 and 21 eV photon energy, with experiments at the BaDELPH beamline of the ELETTRA synchrotron radiation facility), observing a moderate increase of the electron attenuation length and, thus, a moderate increase of the information depth when we reach the lowest energies. By lowering the photon energy below about 11 eV a prominent peak at the Fermi level is observed. The analysis of its intensity variation versus photon energy and the comparison of the experimental spectra with ab initio density of states ( DOS) calculations allow to attribute this structure to a p band crossing the Fermi level, enhanced at selected photon energies due to the influence of the empty DOS, probably amplified by a photoionization cross section effect and by the general increase of the photoelectron yield at low photon energy. In this respect LEPES may thus be considered as a probe of the joint DOS.