In Nd, Sm, Eu and Gd the decay of the 3d-4f resonance excitation into different photoionization channels (4f, 4d) was measured. Spin-orbit splitting of the 3d hole dominates the spectra. Depop- ulation of the 3d32 due to the M4M5N57 Auger effect leads to a much larger 3d52:3d32 int than in absorption. The use of synchrotron radiation from an undulator was decisive.

After almost ten years of successful operation at a bending magnet beamline of HASYLAB, the Flipper monochromator was transferred to a 32-pole wiggler/undulator. With new grazing incidence optics the original energy range of 15–450 eV could be extended to more than 1500 eV. The gain in intensity is approximately two orders of magnitude. Undulator effects are observed between 36 and 900 eV and contribute considerably to this intensity gain. Monochromators of the Flipper type are ideally matching the emission characteristics of undulators. The main problem with wigglers at high energy storage rings is the heat load on the optical elements.

Recently we have investigated the 4d → 4f giant resonances in electron and H+-ion yield spectra of oxidized Sm, Eu,and Yb [1]. Here we report on a continuation of this experiment, i.e., PSD from a metal overlayer system which consists of oxidized Yb on bulk Sm metal. Experiments were carried out at the Hamburger Synchrotronstrahlungslabor HASYLAB at the storage ring DORIS with the FLIPPER-monochromator. Photoelectron spectra were recorded with a commercial double-pass cylindrical mirror analyzer (CMA). A time-of-flight (TOF) mass analyzer utilizing the time structure of the storage ring was used for the detection of the photon-stimulated desorbed ions.

The resonant enhancement in photoelectron spectra at the 4d edges of rare earth atoms and metals is also found in yield spectra of desorbed ions from the surfaces of the oxides of Sm, Eu and Yb following the photon excitation. The analysis of the 4d → 4f resonance leads to a picture of an indirect mechanism of ion desorption which is mainly caused by the flux of energetic 4f photoelectrons from the bulk. In this case the dominant desorption through secondary processes limits the use of the photon-stimulated desorption (PSD) to determine to which type of atom the desorbing species was attached.

The surface core level shift of the 4f72 level in a Pt2%Au and a Pt15%Au alloy has been investigated using high resolution synchrotron radiation excited photoelectron spectroscopy. The bulk and surface components in the recorded spectra have been extracted using a curve fitting procedure. The chemical shifts and the bulk-to-surface intensity ratios are consistent with a strong enrichments of Au to the alloy surfaces. The chemical shifts on nonsegregated surfaces have been measured on these alloys and on a Pt90%Au alloy using conventional XPS.

The development of the ytterbium valence band region was followed with Synchrotron radiation induced Photoemission Spectroscopy (SPS) by interdiffusion of Yb into a Ni (110) single crystal in order to identify the valence conditions of Yb in the bulk and on the surface. During this process, also the width of the Ni L3VV Auger transition was investigated with X-ray induced Photoemission Spectroscopy (XPS), reflecting the electron donation of Yb to the Ni valence band. By comparison between theory and experiment, strong multiplet splittings were found to take place in the 4d and 5p core level spectra of Yb due to the promotion of one 4f electron to the valence band by reaction with Ni. The 5p level is demonstrated to resonate strongly at hν=181 as a consequence of the 4d–4f giant resonance.

Photoelectron spectra of the 4f core level in polycrystalline hafnium were recorded using synchrotron radiation. The emission from both surface atoms and bulk atoms was identified in the spectra. The surface core levels were found to be shifted 0.42+or-0.04 eV towards higher binding energies, in agreement with current theoretical calculations.

The oxidation-induced valence change of Yb leads to a single $4f$ hole in the ground state. The creation of the $4{f}^{13}$ configuration which does not exist for any pure rare-earth metal makes it possible to analyze the $4d\ensuremath{\rightarrow}4f$ Fano resonance for a simple system experimentally as well as theoretically. Calculated Fano profiles for the $4{f}^{12}$ final-state multiplets are in good agreement with photoemission measurements taken with the FLIPPER monochromator at Hamburger Synchrotron-strahlungslabor, Deutsches Elektronen-Synchrotron, using synchrotron radiation from the storage ring DORIS.

The electronic structure of the valence bands of polycrystalline films of pyridine (C5H5N), including all valence levels extending from initial energies of 4 down to 30 eV (EVAC = 0), has been determined from photoelectron energy distribution measurements for photon energies 20eV ⩽ hν ⩽ 170 eV, using synchrotron radiation. The valence bands showing a one-to-one correspondence to the gas phase, a rigid relaxation shift of δer = 0.3 eV for the vertical binding energies, and a considerable solid state broadening (≳ 0.5 eV) are assigned in comparison to recent MO calculations. By tuning the photon energy and thereby achieving high surface sensitivity for hν around 45 eV, we have also studied pyridine adsorbed at 120 K (6 Langmuir) on in situ prepared polycrystalline Ag-substrates. Thus, we were able to study in detail the surface electronic structure in the range of the Ag 4d bands. Due to a strong mixing of substrate 4d and pyridine 2b1 (π), 1a2 (π) and 7a1 (n) energy levels, the surface electronic structure is strongly modified in the upper part of the 4d bands, and a strong and sharp (0.4 eV FWHM) surface resonance at an energy of 3.7 e V below EAGF is observed, which we attribute to a 4d-7a1 (n) bonding of the nitrogen lone-pair orbital.

Photoemission experiments on mixed valent Yb-Al compounds prepared by diffusing Yb into an Al(110) single crystal are reported. At high Yb concentrations surface core level peaks reveal a purely divalent surface in agreement with recent results for single crystal YbAl2. In the dilute limit, when the intensity from bulk Yb is reduced below the limit of detection, a surface layer of divalent Yb still persists and a surface segregation of Yb in Al is made evident. When the bulk concentration of Yb is reduced the bulk mean valence increases. For diluted samples, when the formation of YbAl3 in a surrounding of elemental Al is expected, Yb is still in a mixed valent state. The highly resolved structures from trivalent Yb are compared with a recent calculation of the 4f13 → 4f12 multiplet pattern.

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 Eu2+ and Eu3+ ions in the sample with a close correspondence to mixed-valence Eu3O4. At elevated temperature (400°C) only Eu2+ is found.

Partial photoyield measurements have been performed on the graphite intercalation compounds C6Li and C8K and on pure highly oriented pyrolytic graphite. These experiments probe the local unoccupied electron states on each type of site. It is found that C π∗ states contribute to the density of states at EF in the intercalation compounds as expected, and that the empty Li2p and K3d states lie close to the respective vacuum levels but do not contribute to the density of states at EF.

The complex multiplet structure of the partially filled 5f shell in the actinides is calculated in intermediate coupling. The eigenfunctions obtained are used for a calculation of photoemission intensities in the fractional parentage scheme including all final states. The calculated spectra are significantly different from the equivalent results for the 4f states in the rare-earth metals presented recently.

FLIPPER is a monochromator with fixed entrance and exit beams covering the energy range from 20 to 500 eV used for photoemission measurements with synchrotron radiation.

The two techniques employed for studying the empty conduction band states in stage-1 graphite intercalation compounds (here C 6 Li and C 8 K) provide complementary information. The photoyield experiments give the local (site decomposed) densities of unoccupied states and probe, in particular, the C π ∗ band and the Li(2p) and K(3d)/(4s) states. The high energy Bremsstrahlung isochromat spectroscopy (BIS) data appear to enhance transitions to the C σ ∗ bands. The photoyield experiments show clearly the presence of C π ∗ states at E F but indicate negligible contributions to the densities of states at E F from Li(2p) states and K(3d) states. The shift of E F into the conduction band is not completely rigid band-like, but the main features are observed ∼1 eV closer to E F in C 8 K and ∼2 eV closer in C 6 Li. The strong dependence of the intensity of observed peaks on the excitation polarization direction should contribute to the identification of their band origins if such effects are taken into account in band structure calculations.