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Abstract: K-edge X-ray absorption and 2p-XPS spectra of 3d-element oxides present spectral features which cannot be explained within a simple one-electron model. These features reveal the fine electronic structure of transition metal (TM) oxides valence states resulting from hybridized TM-3d and O-2p states, and the correlations between these valence electrons. In this paper, we show how resonant electronic spectroscopy (resonant Auger or resonant photoelectron spectroscopy) around the TM K-edge can be used to interpret the structures of the threshold and, with the help of theoretical calculation, to determine the electronic configuration of the excited ion. Quadrupolar transitions towards localized 3d orbitals are hence detected and quantitatively characterized in the titanium K-edge prepeaks in TiO2 and in the Ni K-edge prepeaks in NiO by angular-dependent resonant KLL Auger measurements. Valuable information also seems to be available in the resonant behavior of 2p-XPS spectra of NiO and Fe2O3. [Copyright &y& Elsevier]

In this paper we review a variety of spectra for Ce compounds, i.e. valence photoemission and inverse valence photoemission, core-level and resonant photoemission as well as X-ray absorption, X-ray emission and X-ray magnetic circular dichroism (MCD). Those spectra are theoretically analysed by using the single-site Anderson model with various final state interactions. In the first part of the present article we are considering intermetallic Ce compounds, especially several Ce–Pd ordered phases, as well as CeRh3, CeSn3 and CeFe2. In the second part we focus on insulating Ce compounds like CeF3 as well as related systems like Ce oxides. Also we compare Ce hydroxides to other rare-earth hydroxides. Discussions are given on the physical information derived from the analysis, especially through a few key parameters of an extended version of the previously considered Anderson model. Those parameters (i.e. the Coulomb interaction Ufd between 5d and 4f electrons as well as the core hole potential -Udc acting on the 5d electron) have necessarily to be taken into account in order to interpret the experimental L3 X-ray absorption spectra. Another important point stressed in the present paper is the surface/bulk sensitivities of the various spectra to be investigated and theoretically analysed. Also similarities and differences in spectral features between metallic and insulating systems are pointed out. [ABSTRACT FROM AUTHOR]

Near-edge structures in K-edge x-ray absorption spectra (XAS) are widely investigated to understand the electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single-particle approach, for example, has generally limited itself to the dominant dipolar cross section. It has long been known, however, that effects beyond this approach should be taken into account, due to both the inadequacy of such calculations when compared to experiment and the presence of shakeup many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra, and the question is first how to account for it theoretically and second how to verify it experimentally. By using state-of-the-art first-principles electronic structure calculations and li photoemission measurements, we demonstrate that shakeup many-body effects are present in if-edge XAS dipolar spectra of NiO, CoO, and CuO at all energy scales. We show that shakeup effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shakeup effects in if-edge XANES of most correlated transition-metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure. [ABSTRACT FROM AUTHOR]

Abstract: We report photoelectron diffraction (PED) experiments of weakly sub-stoichiometric TiO2(100) rutile surfaces. Apart from standard core-level PED from the Ti-2p3/2 line, we have studied valence band PED from the defect induced Ti-3d states in the insulating band gap. For maximum yield, the latter were resonantly excited at the Ti-2p absorption edge. The PED patterns have been analyzed within the forward scattering approximation as well as by comparison with simulated PED patterns obtained in multiple scattering calculations. The analysis shows that the defect induced Ti-3d charge is mainly located on the second layer Ti atoms. [Copyright &y& Elsevier]

Abstract: Analyses of hard X-ray resonant photoelectron emission spectroscopy (HAX-RPES) and related spectroscopies such as X-ray absorption spectroscopy (XAS) and resonant X-ray emission spectroscopy (RXES) are made for mixed valence Ce compounds with single impurity Anderson model. First, the spectra of Ce XAS ( XAS) and the conventional Ce 3d X-ray photoelectron emission spectroscopy (XPS) are analyzed for , taking into account the bulk/surface sensitivity in XPS. Then it is shown that the bulk properties are more directly obtained from the Ce 3d HAX-RPES spectra, in which the Ce 2p–5d excitation is followed by the Ce 2p3d5d Auger decay. Furthermore, the Ce 3d HAX-RPES can reveal some hidden structures in the Ce XAS. From the analysis of the Ce HAX-RPES for , we reveal the existence of the Ce contribution in the XAS, and confirm an important role of the Coulomb interaction between Ce 4f and 5d elctrons in the XAS structure. For ferromagnetic mixed valence Ce compound , the spectra of the XAS and its magnetic circular dichroism (MCD-XAS) are analyzed, and the effect of is also important in explaining the relative peak positions of the XAS and MCD-XAS. Finally, the MCD in RXES (MCD-RXES) is calculated for , and it is predicted theoretically that the excitation spectrum of MCD-RXES can also reveal the hidden structure of the configuration in the Ce XAS (and MCD-XAS) spectrum. [Copyright &y& Elsevier]

We present a detailed study of the crystallographic structure and morphology of Co/Cu(1 1 11) films by surface extended X-ray absorption fine structure (SEXAFS) and scanning tunneling microscopy (STM). At the very beginning of the growth, the step array is profoundly altered, and large terraces about two times larger than on the clean substrate are formed. For higher thicknesses, islands are observed on the surface. They are first isotropic, and then begin to elongate along the initial step edge direction around 1 ML, and relative straight steps are retrieved around 5 ML. The SEXAFS measurements show that the lattice parameter of cobalt is expanded parallel to the surface but Co is not in a pseudomorphic epitaxy at the beginning of growth because of the relaxation processes at islands free edges. An in-plane structural anisotropy is found only for a Co coverage around 0.7 ML. Upon increasing the thickness, Co adopts a face centred tetragonal structure like on a flat Cu(0 0 1). These results show that the step-induced magnetic anisotropy does not originate from an in-plane crystallographic anisotropy but it is more likely due to the shape anisotropy (i.e. morphology of the films). [Copyright &y& Elsevier]

The magnetism of atomic chains and layers is sensitive to tiny changes in the crystallographic structure and in the lattice parameters of few hundredth of Å. EXAFS is known to be sensitive to such small changes. Here we present an EXAFS study of Co chains and layers grown on a stepped Pt(9 9 7) surface. As a result, we see that the misfit between Co and Pt is too high to permit a perfect pseudomorphic epitaxial growth of cobalt, even for 0.25 ML (a coverage where Co forms wires of 2 monoatomic width). The in-plane interatomic distance between Co atoms varies from 2.66 Å for 0.25 ML to 2.56 Å for 2 ML. We find no in-plane crystallographic anisotropy and the width of the radial distribution around Co atoms function is very large. [Copyright &y& Elsevier]

Resonant spectroscopies offer a new opportunity to get more insight into excited electronic states by studying line shapes and intensities of decay processes. For photon excitations in the pre-K-edge region, the Ti KL[sub 2,3]L[sub 2,3] Auger spectra in TiO[sub 2] show additional peaks when an electron is promoted in localized d-like states via a quadrupolar transition. This resonant process is used to unravel the respective contributions of quadrupolar and dipolar transitions to the absorption edge prepeaks. [ABSTRACT FROM AUTHOR]

Thin magnetic films deposited on single-crystal substrates are well known to present magnetic properties that cannot be found in bulk solids. Thin Co films grown on stepped Cu(1 1 n) surface show a step-induced uniaxial magnetic anisotropy which has been discussed as a magnetoelastic effect or within the Ne´el model considering missing bonds at the step edge. We present a detailed study of the crystallographic structure and morphology of Co/Cu(1 1 11) films by scanning tunneling microscopy (STM) and surface extended X-rays absorption fine structure (SEXAFS). We show that from 3 to 8 monolayers (ML), Co adopts a face centred tetragonal structure like on a flat Cu(0 0 1) substrate. For 1 ML, the first nearest neighbour shell is the same as in Cu in all directions, showing a step-induced stress in the [0 0 1] direction. This structure is related to large islands on the surface. Moreover, at low coverage, STM images show a restructuring of the substrate in order to reduce the surface energy. For 8 ML, we retrieve straight steps but the terraces are about two times larger than on the clean copper. This morphology may be stabilised by the tetragonal structure. These results show that the step-induced anisotropy does not originate from an in-plane structural anisotropy but is more likely due to the shape anisotropy (i.e. morphology of the Co films). [Copyright &y& Elsevier]

The bidimensionnal character of thin magnetic films deposited on single-crystal substrates, together with the occurrence of singular crystallographic structures, often confer on these systems electronic properties that cannot be found in bulk solids. For example, thin Ni layers deposited on Cu(001) present a perpendicular magnetic anisotropy in a very wide thickness range. We will show that this can be explained by a distorted structure of Ni, originating from the strain induced by the epitaxy on the Cu substrate. In this field of 2D magnetism, nanostructures are now investigated. Thin Fe layers on MgO(001) were cut into stripes by the "atomic saw" method: a compression of the substrate induces a dislocation slipping which saws both the substrate and the Fe film in regular and separated ribbons. The observed perpendicular to the stripes magnetization easy axis will be explained by a structural relaxation occurring during the structuration process. In these two studies, a precise structural characterization and simple magnetoelastic models allow one to describe the magnetic behaviors of these systems. [ABSTRACT FROM AUTHOR]