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Soft x-ray resonant photoemission spectroscopy has been used as a tool to investigate the cerium 4f electronic levels of a single-crystalline sample of CeCo2Ge2. Temperature-dependent angle-integrated and angle-resolved results are discussed. For the lowest investigated temperatures two distinct 4f spectral features are clearly observed close to the Fermi level: the Kondo resonance and its lower lying spin–orbit partner. As the temperature is increased, the intensity of such features evolves consistently with the theoretical predictions of the single-impurity Anderson model. However, the angle-resolved results show momentum-dependent effects that require a modification of the single-impurity theory.

In this paper we report a photoelectron spectroscopy (XPS and UPS) study of films of a benzylic amide [2]catenane on Au(1 1 1). We show that this molecule retains its molecular integrity during sublimation and that it chemisorbs on the metal surface. Potassium intercalation modifies the electronic structure of the films. We have observed a reduction of its amide functions and a modification of the charge density of the aromatic rings. The creation of polaron-like states in the gap of the neutral catenane and a decrease in the catenane work function of 0.8 eV have been demonstrated.

Thiol-functionalised catenane and rotaxane thin films were investigated in order to understand the self-assembly of such complex molecules on Au(111). Adsorption from the liquid phase at 300 K leads to the formation of overlayers without long-range order, as evidenced by high-resolution electron energy-loss spectroscopy (HREELS). As expected for thiol adsorption, the sulfur 2p binding energies determined by X-ray photoelectron spectroscopy (XPS) are consistent with the formation of thiolate surface intermediates. The properties of these films are explored as a function of annealing. Changes in vibrational spectra such as the emergence of a AuO band and variations in core-level binding energies and intensities reveal molecular rearrangement due to partial desorption. In addition, based on coherent domain sizes estimated by the angular width of the elastic beam intensity, annealing promotes long-range order within the adlayers.

A new series of palladium (II) fluorides has been prepared. The A 2 PdF 6 compounds crystallize in the orthorhombic space group Cmca . The structure of Ba 2 PdF 6 ( a =17.09(2) A, b =6.163(2) A, c =6.158(1) A, Z =4) has been refined from single crystal data to conventional R 1 =0.0325 (w R 2 =0.0948) for 661 independent reflections. A Rietveld analysis of BaSrPdF 6 and refinement of the lattice parameters of Pb 2 PdF 6 have confirmed the same cationic distribution. Pd II ions are fourfold-coordinated to fluorine. The isolated [PdF 4 ] 2− square-planes form layers, perpendicular to the a -axis, interleaved by bilayers of [ A F 8 ] 6− antiprisms.

We report on two independent measurements of the spin polarization at the Fe 3 O 4 / γ - Al 2 O 3 interface. Fe 3 O 4 / γ - Al 2 O 3 (1 1 1) bilayers have been epitaxially grown by oxygen-assisted molecular beam epitaxy onto α - Al 2 O 3 (0 0 0 1) substrates and some were covered ex situ by a cobalt electrode. Spin resolved photoemission yield to a negative spin polarization ( ≃ - 40 %) while transport measurements on Fe 3 O 4 / γ - Al 2 O 3 / Co magnetic tunnel junctions show a positive TMR, which suggest that the tunnel spin polarization at the Fe 3 O 4 / γ - Al 2 O 3 interface is positive.

A series of copper(II) and rare earth fluorides has been prepared. The crystal structure of NaGdCu 2 F 8 has been solved from single crystal data and refined to conventional R=0.028 (wR=0.048) for 585 independent reflections. The symmetry is tetragonal (space group I422) with a=5.407(1) and c=10.382(1) A (Z=2). A Rietveld analysis of NaYCu 2 F 8 and refinements of the powder X-ray diffraction data for the other compounds of the series confirmed the I422 space group. The structure consists of layers of CuF 4 square-planes perpendicular to the c-axis, interleaved alternatively by Na + or RE 3+ cations located in antiprisms.

We present recent results of time-resolved x-ray photoemission electron microscopy on permalloy microstructures. The stroboscopic experiments feature a time-resolution of Deltatauless than or equal to130 ps. We observe a strong influence of incoherent magnetization rotation processes, leading to a significant transient stray-field formation at the edges of the microstructure. (C) American Institute of Physics.

We present results of a direct imaging approach to visualize the dynamics of magnetic domains on the nanosecond scale. The experiments are carried out by means of an x-ray photoemission electron microscope (X-PEEM) in a stroboscopic mode and exploit the intrinsic time structure of the synchrotron radiation delivered by the storage ring facility ESRF (Grenoble). In this way we combine the high lateral resolution of a PEEM with a subnanosecond time resolution.

The discovery of giant magnetoresistance in Fe/ Cr multilayers 1 has been followed by a large research effort for almost two decades aiming at developing new materials suitable for spintronics. The interest of a given material is mainly expressed by its spin polarization P =N↑ �N↓ /N↑ +N↓, N↑ N↓ standing for majority spin minority spin electron density of states at the Fermi level. This property is particularly important for magnetic tunnel junctions stacks of two magnetic electrodes separated by a thin insulating layer. 2 Indeed, the tunnel magnetoresistance TMR, corresponding to the variation of resistance between parallel and antiparallel configurations of the electrode magnetizations, is given in a simple view by the Julliere formula: 3 TMR =2 P1P2 / 1� P1P2, P1 and P2 being the spin polarizations of the two electrodes. Magnetite Fe3O4 is thus expected to be an interesting electrode material, for band structure calculations predict a half metallic behavior P = �100%, the con

The pure Fano effect in angle-integrated valence-band photoemission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photoelectrons has been avoided by an appropriate choice of the experimental parameters. The theoretical description of the resulting spectra reveals a complete analogy to the Fano effect observed before for paramagnetic transition metals. While the theoretical photocurrent and spin-difference spectra are found in good quantitative agreement with experiment in the case of Fe and Co, only a qualitative agreement could be achieved in the case of Ni by calculations on the basis of plain local spin-density approximation. Agreement with experimental data could be improved in this case in a very substantial way by a treatment of correlation effects on the basis of dynamical mean field theory.

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in ${\mathrm{L}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}$ is strongly reduced from its ionic value, both below and above the N\'eel temperature. Using Ti ${L}_{2,3}$ x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the ${t}_{2g}$ subshell is about 0.12--0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.

The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa–Kohn–Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented.

Results of a combined experimental and theoretical investigation on the Fano-effect in the angle-integrated valence band photoemission of the noble metals are presented. In line with the fact that the Fano-effect is caused by the spin-orbit-coupling, the observed spin polarization of the photocurrent was found to be the more pronounced the higher the atomic number of the element investigated. The ratio of the normalized spin difference curves, however, agreed only for Cu and Ag with the ratio of the corresponding spin-orbit coupling strength parameters. The deviation from this expected behavior in the case of Au could be explained by the properties of individual $d\text{\ensuremath{-}}p$- and $d\text{\ensuremath{-}}f$-contributions to the total spin difference curves, that were found to be quite different for Au compared to Cu and Ag.

The work presented in this thesis aims at achieving an increased understanding of the electronic structure of materials whose properties are to a large extent governed by transition metals. All studies are based on data from angle-resolved photoelectron spectroscopy (ARPES) employed on the valence band of the studied systems. In some cases spectroscopic data have also been combined with numerical electronic structure studies performed using a density functional theory computer code. Five of the studies make extensive use of the benefits provided by performing angle-resolved photoelectron spectroscopy at high photon energies. When probed with soft x-ray photons, the near Fermi edge distribution of spectral weight in Nd2-xCexCuO4 and La2-x-yNdySrxCuO4 display significant differences as compared to similar studies performed in the 20-100 eV range of photon energies. This effect can be attributed to the approximate two-fold increase in probing depth as compared to the low photon energy case. However, high photon energies not only give increased probing depth, it also enables a straightforward interpretation of ARPES data from fully three-dimensional compounds in terms of valence band energy dispersion. This principle has been used to study the dispersions in the transition metal oxides CoO and Cu2O as well as in a proof-of-principle study, where copper was used as a test case. CoO exhibits a magnetic phase transition at the Neel temperature, from a paramagnetic state into an antiferromagnetically ordered state. The presented data show a significant shift of spectral weight between different band structure regions as the sample temperature is elevated across the Neel temperature. The Cu2O ARPES data have confirmed the existence of a hybridized Cu 3d - Cu 4s state. Through comparision with theoretically calculated results, a refined value of the Hubbard potential U has been determined. An extensive ARPES dataset from copper, covering the entire Brillouin zone, has in a proof-of-principle study been used to derive the binding-energy resolved valence band charge density. Two ARPES studies of the La2-x-yNdySrxCuO4 system have been performed in the cnventional low photon energy range. The high energy resolution has enabled a detailed study of dispersive features in the near Fermil level region of the valence band.

Orbital ordering (OO) in the layered perovskite La 0 . 5 Sr 1 . 5 MnO 4 has been investigated using the enhanced sensitivity of soft x-ray resonant diffraction at the Mn L edges. The energy dependence of an OO diffraction peak over the L 2 , 3 edges is compared to ligand-field calculations allowing a distinction between the influences of Jahn-Teller distortions and spin correlations. The energy dependence of the diffraction peak at the Mn L 1 edge is remarkably different from that observed at the Mn K edge.

Spin-resolved photoemission from ferromagnetic Ni has been measured using circularly polarized x rays, which allowed us to obtain the difference spectra, i.e., the magnetic circular dichroism, the spin spectrum, and the spin-orbit spectrum from the same data set. The results are compared with calculations for the final-state impurity model in which the core-ionized atom is described as an impurity within a many-body formalism. A good agreement between experiment and theory is obtained for all difference spectra, although the spin-orbit spectrum shows an increased spin-polarized background. We also quantified the relation between the 2p spin-orbit spectrum and the L 2 , 3 x-ray magnetic circular dichroism.

We have performed an angle resolved photoemission study on a single crystal of the optimally electron doped (n-type) cuprate superconductor Nd2-xCexCuO4 (x=0.15) at a photon energy of 400 eV. The Fermi surface is mapped out and is, in agreement with earlier measurements, of hole-type with the expected Luttinger volume. However, comparing with previous low energy measurements, we observe a different Fermi surface shape and a different distribution of spectral intensity around the Fermi surface contour. The observed Fermi surface shape indicates a stronger electron correlation in the bulk as compared to the surface.

Orbital ordering (OO) in the layered perovskite La0.5Sr1.5MnO4 has been investigated using the enhanced sensitivity of soft x-ray resonant diffraction at the Mn L edges. The energy dependence of an OO diffraction peak over the L(2,3) edges is compared to ligand-field calculations allowing a distinction between the influences of Jahn-Teller distortions and spin correlations. The energy dependence of the diffraction peak at the Mn L1 edge is remarkably different from that observed at the Mn K edge.

The electronic structures of nickel and copper have been studied for KMF3 and K2NaMF6 compounds by a-ray absorption spectroscopy at the Ni and Cu L-2.3 edges in order to characterize the M-F chemical bond. The spectral features have been interpreted based on the mixing of two ground-state configurations \3d(n)) +\3d(n+1)](L) under bar. Multiplet calculations were used to simulate each spectrum in order to quantify the charge transfer from fluorine to the transition metal yielding a 40% ground-state contribution of the 3d(8) configuration for K2NaCuF6 and 65% of the 3d(7) configuration for K2NaNiF6.

In this paper, spin-resolved photoemission through an oxide barrier, the polarization of NiMnSb/MgO(001) and Fe/MgO(001) interfaces are studied.

Single-crystalline (001) Fe thin films were prepared by molecular beam epitaxy and covered by epitaxial MgO barriers. The MgO growth was confirmed to be layer by layer as shown by reflection high-energy electron diffraction, which allowed us to prepare Fe films covered by only two atomic planes of MgO for spin polarization measurements. On the one hand, regular x-ray photoemission spectroscopy measurements evidenced a weak hybridization between Fe and O. Moreover, a large Fe magnetic moment at the interface with MgO was shown by x-ray magnetic circular dichroism measurements. These two observations are in agreement with theory. On the other hand, we show that the Fe density of states can be measured by photoemission through the oxide barrier, since the oxide valence band only starts at 4 eV below the Fermi level. Spin-resolved x-ray photoemission measurements performed at ESRF allowed us to demonstrate that the electrons emitted from the (001) Fe layer through the barrier are polarized. A polarization fully integrated in k space and corrected from remanence near 42% was measured.