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Amorphous alloys exhibit useful properties such as the excellent soft magnetic behaviour of Fe-based metallic glasses. The detailed structure of amorphous $$\text {Fe}_{(1-x)}\text {Zr}_x$$ Fe ( 1 - x ) Zr x with x = 0.07, 0.10, and 0.20 is in this work explored through a synergetic combination of atomistic simulations and experimental characterisation. Thin-film samples were investigated using X-ray diffraction and extended X-ray absorption fine structure (EXAFS), while the corresponding atomic structures were simulated using an efficient first-principles-based method called stochastic quenching (SQ). The simulated local atomic arrangements are investigated by constructing the radial- and angular-distribution functions, as well as by Voronoi tesselation. The radial distribution functions are then used to construct a model to fit simultaneously the experimental EXAFS data of multiple samples with different compositions, creating a simple yet accurate description of the atomic structures valid for any composition in the range x = 0.07 to 0.20, using a minimal number of free parameters. This approach significantly improves the accuracy of the fitted parameters and allows us to relate the compositional dependence of the amorphous structures with the magnetic properties. The proposed EXAFS fitting process can be generalised to other amorphous systems, contributing to the understanding of structure-property relationships and the development of amorphous alloys with tailored functional properties.

International audience; One of the most attractive characteristics of some Prussian blue derivatives is the sensitivity of their magnetic properties to the irradiation with light. In this work photoinduced effects in the (Fe0.2Cr0.8)1.5[Cr(CN)6]·15H2O PBA have been studied by means of X-ray-based spectroscopies and magnetometry. It is found that the photosensitivity of this compound is mostly centred on the Fe cations: the exposure to green light induces a transfer of electrons from them to the Cr that provokes a reversal of the previously existing linkage isomerization and increases the elastic strain caused by the misfit of the unit cells of the Fe–NC–Cr and Cr–NC–Cr sublattices. The green light also quenches the magnetism of the FeII high-spin (HS) ions present in the sample and reduces the magnetic moments of most of the Cr cations except for CrII HS. Our study highlights the important role played by the mismatch between the unit cells of the coexisting sub-lattices in ternary Prussian blue analogues.

We characterise the magnetism of self-assembled FenN nanocrystals, combining core level spectroscopy with first-principles theory. Not only ferromagnetic but also antiferromagnetic iron nitride nanocrystals are identified, exhibiting stable magnetic properties at room temperature. New stable magnetic phases are found, previously believed to order magnetically only well below room temperature. As determined by the growth conditions, several phases of magnetic FenN nanocrystals are identified in the near surface region of GaN based thin films, with typical dimensions from 50 to 100 nm, embedded in the (Ga,Fe)N lattice or residing on the GaN surface. We determine, at room temperature, Fe4N and Fe3N ferromagnetic nanocrystals, as well as Fe2N and FeN nanocrystals in an antiferromagnetic state, which is not stable at room temperature in their bulk phases.

The assembly of two diphenylethylenediamine enantiomers, separately deposited on Cu(100), is investigated from the first stages of two-dimensional crystallization to the nucleation and growth of the second layer. By means of scanning tunneling microscopy, we show that the chirality of enantiomers is expressed at different levels of molecular organization. Below the monolayer completion, a disordered phase coexists with domains of a square lattice aligned with the principal crystallographic directions of the substrate. The intrinsic chirality of the molecules is only manifested through specific features contained within the corresponding unit cell. For increasing coverage, this arrangement is accompanied by a second square structure, which appears to be clockwise or counterclockwise rotated with respect to the Cu(100) directions depending on the enantiomer. The nucleation of molecular chains on top of the aligned square structure gives rise to a second layer exhibiting a stripelike configuration with remarkable left- or right-handed helicity that mirrors that of the particular enantiomer. The nearly flat configuration of the first-layer molecules is confirmed by angular-dependent X-ray absorption experiments and supported by molecular dynamics simulations., This work has been supported by the Spanish Government under projects MAT2013-47869-C4, MAT2014-59315-R, MAT2015-72848-EXP/AEI, FIS2016-74893-P, and MAT2016-77852-C2-1-R (AEI/FEDER, UE) and the Generalitat de Catalunya 2017 SGR 668. We also appreciate the specific agreement between ICMAB-CSIC and the Synchrotron Light Facility ALBA and the Spanish MINECO through the project MAT2015-68994-REDC and the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2015-0496). The NEXAFS experiments were performed at BOREAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. IMDEA Nanociencia acknowledges support from the “Severo Ochoa” Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). R.P.-R. thanks the financial support through BES-2014-067942 (FPI fellowship). We acknowledge the CESGA Supercomputing Center for computational time at the Finisterrae Supercomputer and technical assistance.

The adsorption of purely organic chiral molecules on ferromagnetic Co thin films is studied under ultra high vacuum conditions by means of synchrotron radiation-based electron spectroscopies, namely X-ray absorption and ultraviolet photoemission. X-ray absorption reveals that enantiomers with opposite handedness (R,R)– and (S,S)– of two different molecules adsorb with different strength on the Co surfaces and their valence band photoemission spectra also display distinctive features. In view of the recent reports describing the chiral-induced spin selectivity (CISS) effect these results lead us to consider the possibility that some enantiosensitivity may appear when bonding chiral molecules to a substrate with an initial asymmetry in the population of the different spin orientations.

Spinel-type compounds of Fe–Ni–Sb–O system were synthesized as polycrystalline powders. The crystal and magnetic properties were investigated using X-ray and neutron powder diffraction, Mossbauer and X-ray absorption spectroscopy and magnetization measurements. The samples crystallize in the cubic system, space group Fd – 3 m. The distribution of cations between octahedral and tetrahedral sites was refined from the diffraction data sets using constraints imposed by the magnetic, Mossbauer and EDS results and the ionic radii. The cation distribution and the temperature dependence of the lattice parameter (a) and the oxygen positional parameter (u) were obtained. A chemical formula close to Fe0.8Ni1.8Sb0.4O4 was determined, with Sb5+ cations occupying octahedral sites, and Fe3+ and Ni2+ occupying both tetrahedral and octahedral sites. Fe3+ mainly (85/15 ratio) occupy tetrahedral sites, and conversely Ni2+ mainly reside on octahedral ones. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The results indicate that the compounds have a collinear ferrimagnetic structure with antiferromagnetic coupling between the tetrahedral (A) and octahedral (B) sites. Uniquely, the temperature dependence of the net magnetization of this rare earth free ferrimagnet exhibits a compensation point.

Aim: To determine the efficacy of optical coherence tomography angiography (OCT-A) in diagnosing optic nerve head flow impairment in patients with optic nerve drusen. Methods: Patients affected by optic-nerve head drusen (ONHD) attending the Eye Clinic of the Federico II University of Naples were enrolled in this prospective case series between October 2015 and October 2016. Each patient underwent evaluation of best corrected visual acuity (BCVA), Goldman applanation tonometry, slit-lamp biomicroscopy, fundus examination, standard visual-field testing (perimetry), spectral domain (SD)-OCT and OCT-A. Results: Thirteen patients (6 females and 7 males with a mean age of 22.05 ± 7.54 years) with ONHD (19 eyes) were enrolled. Mean BCVA was 0.16 ± 0.21 LogMar and mean intraocular pressure was 15.68 ± 1.66 mm Hg. The control group constituted 16 individuals (24 eyes). Both ganglion cell complex (GCC) and retinal nerve fiber layer (RNFL) parameters were lower in patients than in controls. Similarly, the flow index (U = 134, p = 0.021) and vessel density (U = 90, p = 0.001) were significantly lower in eyes affected by ONHD than in normal eyes. Visual-field parameters did not differ between the 2 groups. GCC parameters were significantly correlated with OCT-A parameters (p < 0.05). No correlation was found between RNFL and OCT-A parameters. Conclusions: Our data suggest that OCT-A could be an objective method, helpful in the analysis of flow changes in patients with ONHD.

The appearance of magnetic order in the (Fe0.2Cr0.8)1.5[Cr(CN)6]·15H2O Prussian blue analogue at low temperature has been investigated by means of synchrotron radiation-based X-ray absorption spectroscopy and X-ray magnetic circular dichroism. With the help of ligand field multiplet analysis we have been able to identify the oxidation states of the metallic cations present in the sample and their evolution with temperature. Our experiments reveal that the appearance of ferromagnetic order is triggered by the transformation of CrIII cations to CrII high-spin caused by a transfer of electrons from the Fe to the Cr resulting in an increase of the magnetic interactions within the (Cr, Cr) sublattice. The misfit strain between the (Fe, Cr) and the (Cr, Cr) moieties that coexist within this ternary material influences the balance of oxidation states and hence the magnetic properties of the metallic ions. Misfit relaxation also plays a role in determining the differences between the surface and the bulk of the material. The measurement of the magnetic moments in those two regions suggests that the surface may have a reduced Curie temperature compared to the bulk.

The effect of the presence of CeO2 in the source material on the properties of SiC crystals grown by Physical Vapor Transport (PVT) method is investigated. The doping efficiency and, indirectly, the presence of the cerium vapour in the growth atmosphere were examined by study of structural, electrical and optical properties of the crystals. X-ray photoelectron spectroscopy shows that Ce2O3 and CeO2 coexist on the SiC post-growth surfaces. A detectable Ce incorporation is observed only in the last grown part of the crystal.

The implantation of Mn ions into two Si substrates with different doping (P or B), resistivity and oxygen content was performed at low and high substrate temperatures. Different post-implantation p ...

A method for producing self-organised arrays of nanometric metallic dots is reported. It consists on developing first the nanodot pattern by ion erosion on a semiconductor cover film and transferri ...

The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.

We have made in situ investigations of epitaxial ultrathin Fe films on Ag(100). This system is known to exhibit a reorientation of the magnetization, dependent of Fe thickness and temperature. Our aim here is to correlate the local structure with the magnetic properties of this system. The X-ray absorption fine structure has been recorded in situ both in the near edge as well as in the extended X-ray absorption fine structure (EXAFS) range. Using X-ray magnetic circular dichroism we find that, below 300 K, films between 2 and 6 monolayers show an out-of-plane remanent magnetization whereas for thicker films the magnetization lies in-plane. By making use of the Fe L-edge EXAFS we obtain information on the local structure around the Fe atoms, such as the interatomic distances, the coordination number, and the mean square relative displacement of the first neighbor shells. (C) 2003 Elsevier Science B.V. All rights reserved. (Less)

The temperature-driven spin-reorientation transition (SRT) has been investigated in a layer of 2.1 nm Co in Au/Co/Au. We studied the evolution and stability of the in-plane magnetization components in the temperature range from 300 to 90 K by means of polarized neutron reflectometry (PNR) and Co L-edge X-ray magnetic circular dichroism (XMCD) measurements. The PNR measurement provides evidence for the occurrence of a SRT in this temperature range. XMCD can be used as a vector magnetometer that yields both the in- and out-of-plane magnetization components per Co atom. Combining the results of both techniques (PNR and XMCD) allows separating the orbital and spin magnetic moments using magneto-optical sum rules. We observed that already above the SRT the in-plane orbital moment component changes significantly stronger than the spin component.

Electrons photoemitted through layers of purely organic chiral molecules become strongly spin-polarized even at room temperature and for double-monolayer thicknesses. The substitution of one enantiomer for its mirror image does not revert the sign of the spin polarization, rather its direction in space. These findings might lead to the obtention of highly efficient spin filters for spintronic applications.

The interaction of a monolayer and submonolayer N2O with the Cu(1 0 0) and Ag(1 1 0) surfaces has been studied using near-edge X-ray absorption fine structure spectroscopy. From a detailed analysis of the angular dependent intensity of the molecular resonances we derive a substrate and coverage dependent bent of the N2O molecules upon adsorption. From the comparison of the π* resonance intensity from the terminal Nt, and central Nc nitrogen atoms we conclude that the N2O molecules couple with the Cu surface through the terminal Nt atom in contrast to the Ag surface where the Nc atom is involved.

Core level X-ray Absorption Spectroscopy measurements have been performed at the L 3,2 edges of thin film Fe samples deposited on the (100) surface of Cu. Soft X-rays from five different beamlines have been used to measure spectra from identical samples with very different degrees of transverse coherence in the synchrotron radiation. The degree of source coherence has been characterised by diffraction. The transverse coherence length has been extracted and found to be on the μm length scale at certain beamlines. An increase of the L edge resonance intensities, relative to the continuum states, is observed in spectra measured at these beamlines.

We report ab initio calculations of the X-ray absorption cross section for the near edge X-ray absorption fine structure of C 2 H 6 , C 2 H 4 and C 2 H 2 , at the carbon K-edge, based on a full multiple scattering formalism. We find that shape resonances dominate the photoabsorption carbon K-edge spectra close to the edge, leading to a spectacular enhancement in cross section of order 3–4 Mbarn. Our analysis highlights the strong influence of the molecular vibrations on the intensity, asymmetric profile and energy of this spectral feature. Calculations with and without hydrogen atoms, allow to estimate the amount of C–H character of this feature. A quantitative comparison between theory and experiment, using spectra of oriented molecules on surfaces is performed. Molecular orientation in the experiment is obtained by means of physisorption which has the advantage of obtaining molecules very close to their gas phase state.

We report temperature- and angular-dependent surface extended X-ray absorption fine structure spectroscopy (SEXAFS) measurements of the p4g(2 x 2)C/Ni(100) system. Both a Ni(100) single crystal and ...

High-resolution photoabsorption spectra at the N 1s→π∗ resonance of N2 physisorbed on the Cu(100) surface are reported. The vibrational fine structure of this resonance could be resolved, allowing the determination of the vibrational constants, the lifetime and intramolecular distances of the core-excited states of the physisorbed molecules. The obtained fundamental vibrational constants are compared with the corresponding vibrational parameters for the gas phase.

We report ab initio calculations of the x-ray absorption cross section for the near edge x-ray absorption fine structure of C2H6, and C2H4, and C2H2 at the C K-edge, based on a full multiple scattering formalism. The angular dependence of the electric dipole transition in the calculations as well as the angular dependent experiments for the oriented molecules give a good opportunity to compare both. The resonance can be assigned to a sigma(*) shape resonance. The multiple scattering formalism and the experiment agree well and thereby support the existence of such features in the spectra.

Circularly polarized x-ray radiation is attracting increasing interest as a tool for the characterization of the electronic, magnetic, and chiral properties of low-dimensional structures. Using circular light (with electric field vector parallel to the orbital plane), a dependence of the measured quantity by changing either the orientation of the light polarization or the magnetization is indicative of the existence of magnetic circular dichroism. It can be observed in x-ray absorption spectroscopy (XAS), in which the photon energy is scanned through an absorption threshold exciting a core electron into an unoccupied valence state using circularly polarized light. Synchrotron radiation sources have made this technique possible. It can also be observed in photo-emission spectroscopy from core and valence levels. Here we focus on magnetic circular x-ray dichroism (MCXD) in XAS as an element-specific tool to investigate magnetic properties of ultrathin films in situ. The application of magneto-optical sum rules enables the determination of the orbital and spin magnetic moments per atom from XAS spectra, as well as the easy magnetization direction.MCXD-based magnetometry in XAS is extensively used by measuring the L absorption edges of 3d-transition metals, where large intensity changes (up to 60%) of the L-edge white lines are observed upon reversal of either the sample magnetization or the light helicity. The high magnetic contrast obtained, combined with the elemental specificity of the technique, allows for the study of very dilute samples such as ultrathin films. We first concentrate on the selection rules governing MCXD in XAS.

Two new ordered monolayer phases of ${\mathrm{C}}_{60}$ on Al surfaces have been studied using electron spectroscopies and low-energy electron diffraction (LEED). On Al(111), in addition to the previously reported (6\ifmmode\times\else\texttimes\fi{}6) phase formed by evaporating with ${\mathrm{T}}_{\mathrm{sample}}$=620 K, a metastable $(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ phase can be produced with ${\mathrm{T}}_{\mathrm{sample}}$=300 K. This phase exhibits the first LEED pattern reported for an unannealed ${\mathrm{C}}_{60}$ overlayer. On Al(110), when evaporations are also made with ${\mathrm{T}}_{\mathrm{sample}}$=620 K, LEED shows the presence of a monolayer with a pseudo-$c(4\ifmmode\times\else\texttimes\fi{}4)$ structure. Al $2p$ photoemission for ${\mathrm{C}}_{60}$/Al(110) and for $(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ ${\mathrm{C}}_{60}$/Al(111) reveals no evidence of strong substrate reconstruction. The perturbation of the geometric and electronic structure of the ${\mathrm{C}}_{60}$ molecule due to the bonding interaction with the Al surface increases in the order ${\mathrm{C}}_{60}$/Al(110), $(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ ${\mathrm{C}}_{60}$/Al(111), (6\ifmmode\times\else\texttimes\fi{}6) ${\mathrm{C}}_{60}$/Al(111), as demonstrated using element-specific probing of the valence band with x-ray absorption and C $1s$ shakeup. The bond has covalent character in all three cases. Symmetry-induced splitting in the ${5h}_{u}$-derived level is observed using valence photoemission, and is particularly clear for ${\mathrm{C}}_{60}$/Al(110). The stability of the equilibrium structures can be qualitatively understood from considerations of the energetics of the overlayer compression and the chemical bond between adsorbate and substrate. Work-function measurements for these and other ${\mathrm{C}}_{60}$ overlayer systems cannot, in general, be understood within a simple description involving the addition of a dipole to the surface potential.

We report normal and magnetic extended x-ray absorption fine-structure (EXAFS) measurements made on 30 ML Fe films on Cu(001) substrates at the edges. The magnetic EXAFS at the L edges of 3d metals is particularly important as it can be used to probe the magnetism of the d states. Magnetic EXAFS oscillations were detected up to 500 eV above the edge, corresponding to in k-space. Over such a large range, we were able to see long-wavelength wiggles and separate them from Fe nearest-neighbour backscattering and the fast oscillations that had been previously seen. It is shown that without using any deconvolution procedure, a meaningful analysis can be performed despite the interference of the and edges. The experimental data were compared with the results of multiple-scattering calculations, and this enabled us to assign all of the features in both the normal and the magnetic EXAFS Fourier transforms to various single- and multiple-scattering paths. Also, there was found to be less temperature-dependent damping for magnetic EXAFS as than for the normal EXAFS between 75 K and 300 K.

We present photoelectron spectra for the highest occupied molecular orbital (HOMO) of C60 in the gas phase and a two-dimensional (2D) condensed layer. For low temperatures the similarity in the spectra is striking and places a strict upper limit of 0.07 eV on the HOMO electronic bandwidth for the 2D solid, which is a fraction of the theoretically predicted value. This is shown to be consistent with expectations of a polaronic model for the bands and suggests the need fora reassessment of the band dispersions in 3D C60.

We present evidence for atomic site-dependent excitonic effects in the x-ray absorption spectrum of an ordered chemisorbed monolayer of ${\mathrm{C}}_{60}$/Al(110). We observe that the broadening in the ${5t}_{1u}$-derived resonance and the corresponding core level resonant photoemission intensity varies with the x-ray incidence angle. This can be understood as due to changes in the strength of the interaction between the x-ray absorption final state and the substrate bands. This study provides the first direct measurement of the length scale for the localization of an excited state by the core hole.

The presence of oscillatory structures in the atomic x-ray absorption background is reported for the first time for surface-EXAFS of cN/Cu(100) and N/Cu(110). Systematic analysis of this feature (AXAFS) and comparison to theory yields new information on the electronic structure of the adsorbate - substrate surface bond. Also, angle and temperature dependent analysis of the AXAFS peak provides qualitative information about interstitial charge density distribution.

Using magnetic circular X-ray dichroism (MCXD), Co/Ni, Cu/Co and Cu/Ni bilayers and Co/Cu/Ni and Ni/Cu/Co trilayers grown on a Cu(001) substrate were investigated. The Co layers were about 2 monolayers (ML) and the Ni layers were between 1.5 and 4.5 ML thick. It was observed that, for Co/Ni bilayers, the entire system has only one Curie temperature, T c . After having been covered by 2-7 ML Cu, Ni and Co films exhibit a significantly lower Tc. For trilayers, different Curie temperatures were determined for Ni and Co when separated by a 2-6 ML Cu spacer. The coupling of Ni and Co layers was found to be both ferromagnetic and antiferromagnetic, depending on the spacer thickness and the order of the layers.

A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 degrees C show magnetic properties specific to II-V ...

We present a measurement of the C Is ionisation potential (IP) for solid C-60, as well as a reliable determination of the highest occupied molecular orbital (HOMO) IP. The difference between the gas phase and solid state measurements for the HOMO agrees w

We report near-edge x-ray-absorption fine-structure (NEXAFS) and magnetic circular x-ray dichroism (MCXD) measurements of 4-ML Ni films grown on Cu(100). The films were exposed to oxygen which then adsorbed in different adsorption states. The changes in the density of states as probed at the Ni ${\mathit{L}}_{2,3}$ edges, the oxygen K edge, as well as the magnetic response of the sample are investigated simultaneously for the various adsorption states that range from ${\mathrm{O}}_{2}$/Ni at 38 K to an ultrathin film of NiO. The NEXAFS spectra provide a characterization of the changes in the different nickel 3d, 4sp, and oxygen 2p density of states above the Fermi level. These states dominate the interaction of the oxygen and nickel atoms and can be studied separately using the element specificity of x-ray absorption. We find that 0.5 ML of atomic oxygen suppresses the magnetization corresponding to one layer of Ni, and for 1.5 ML no ferromagnetic response from a 4-ML film at 38 K could be detected. \textcopyright{} 1996 The American Physical Society.

A review is given of surface extended X-ray absorption fine structure (SEXAFS) data taken at the N and O K-edges of atomic and molecular adsorbates on Cu and Ni surfaces. The theory of the dynamic analysis of SEXAFS data is briefly presented. We conclude that a dynamic analysis is also necessary in many cases for a reliable structural determination. This result is particularly important in the case of reconstructed surfaces where the structural and dynamic contributions in the SEXAFS amplitude and phase can be of comparable strength. An analysis of the dynamic part of the disorder allows one to distinguish between reconstructed and unreconstructed systems. Furthermore, the use of model pair potentials allows for a discussion of surface reconstruction in terms of simple physical parameters. Finally a short discussion is given of the photon flux and stability required for a state of the art SEXAFS experiment, in view of the availability of the improved third generation soft X-ray sources.

We present photoemission and C 1s photoabsorption data for an annealed monolayer ${\mathrm{C}}_{60}$/Al(111), which show that a strong covalent bond is formed between the ${\mathrm{C}}_{60}$ molecules and the substrate. Low-energy electron-diffraction and scanning tunneling microscopy data reveal a highly symmetric overlayer structure commensurate with the substrate. Al 2p photoelectron spectra show that the chemical environment at the surface is greatly modified compared to clean Al(111), and indicate that a significant fraction of the surface atoms have moved, consistent with a picture of covalent bonding to the overlayer. The strength of the interaction is such that the fullerenes are distorted more than on other metal surfaces or in compounds with alkali metals.

We report magnetic circular X-ray dichroism (MCXD) measurements of ultrathin Ni films grown on Cu(100). The Curie temperature of the films is determined by means of a.c. MXCD susceptibility, a technique that allows T c to be probed precisely and unambiguously. Furthermore, the interaction of submonolayer oxygen with the films, adsorbed in physisorbed molecular and atomic states, is studied. The decrease in the magnetic response of the sample is investigated systematically for various adsorption states of increasing chemisorption strength. The oxygen induced changes in the MCXD difference and in the absorption features measured with linear polarized light provide a better characterization of the electronic states involved in the MCXD response. The magnetism of the Ni films is already influenced by O 2 molecules in a physisorbed state, a c(2 × 2) overlayer of atomic oxygen is found to neutralize the magnetism of two layers of an ultrathin Ni film.

We present soft x-ray absorption spectra from a series of Co doped ZnO films. We discuss systematic variations of the Co L-edge white line intensity and multiplet features for this series of samples. We document sizeable differences in the electronic state of the Co ionic cores, as well as in the local environment of the host lattice atoms, characterised by means of x-ray absorption spectra at the O K-edge and Zn L-edges. Model calculations allow to correlate the observed effects to small structural distortions of the ZnO lattice.

An overview for a dynamical SEXAFS analysis for several systems is presented in terms of effective pair potentials. Model potentials of Madelung type are found to describe well the adsorption of N, ...

Values for the magnetic moments of 3d transition metals have been calculated from magnetic circular X-ray dichroism measurements using sum rules. In this work we reveal that these calculations are sensitive to a damping effect resulting from a decrease in photon penetration at the L3.2 peaks. Known as saturation effects, we present a simple correction to compensate for this phenomenon. We also show that the magnetic moments, as determined using sum rules, are relatively insensitive to the step function fitted to the absorption spectra. The magnetic moments derived from our data differ from the known ground-state moments. The corresponding collective factors appear to be transferable between cobalt and nickel.

We report Magnetic Circular X-ray Dichroism (MCXD) measurements of ultrathin monolayers (ML) and bulk-like Co films grown on a Cu(100) surface. No increase is observed in the orbital magnetic moment of the Co atoms for the ultrathin films in contrast to expectations due to symmetry lowering on the surface. We developed a new ac field modulated MCXD-susceptibility technique permitting accurate measurements of the critical temperature T c . At about 1.8 ML, T c suddenly increases by more than 150 K when the film structure changes from hetero-to homoepitaxial growth.

We present soft X-ray magnetic circular X-ray dichroism (MCXD) measurements at the Ni L edges of thin Ni films on Cu(100) with a thickness between 1 and 7 monolayers. The data were measured around the L 3 edge covering the whole temperature range up to the critical temperature. Furthermore, measurements around both the L 3 and L 2 edges were performed at low temperatures. The temperature variation of the MCXD signal and the critical temperatures of the films as a function of their thickness are discussed and compared to results of other studies

The structural and dynamical properties of molecular oxygen in submonolayer coverage adsorbed on Cu(100) were investigated by means of oxygen K-edge photoabsorption. The adsorption geometry of the O 2 molecules, as well as the disorder and anharmonic contributions to the pair distribution function for the first-nearest-neighbor O-Cu shell were quantitatively determined for well-defined sequential molecular states of physisorption and chemisorption

The interaction of acetonitrile (CH 3 CN) with the clean and the alkali metal (Na, K) promoted Au(100)-(5 X 20) surface was studied by near edge X-ray absorption fine structure (NEXAFS). On clean Au(100), CH 3 CN is essentially physisorbed in an almost flat-lying configuration with an angle of 81° ± 10° between the CCN axis and the surface normal. The molecular interaction with coadsorbed alkali metal atoms reduces the CN bond length by 0.04 A (Na) and 0.07 A (K), respectively. This is the first report of a contraction of an intramolecular bond of an adsorbed molecule in the presence of coadsorbed alkali metal.

Utilizing vector magnetometry by means of X-ray circular dichroism, the temperature-driven spin reorientation from an in-plane to out-of-plane orientation in thin Co films is studied in an epitaxially grown Au/Co/Au trilayer with decreasing temperature. Probing the remanent state by changing the photon helicity provides evidence for a smooth transition and the formation of a metastable magnetic multi-domain state at temperatures below the transition temperature.

We have performed x-ray absorption spectroscopy at the Fe, Ni, and Co L 2,3 edges of in situ grown thin magnetic films. We compare electron yield measurements performed at SSRL and BESSY-I. Differences in the L 2,3 white line intensities are found for all three elements, comparing data from the two facilities. We propose a correlation between spectral intensities and the degree of spatial coherence of the exciting radiation. The electron yield saturation effects are stronger for light with a higher degree of spatial coherence. Therefore the observed, coherence related, intensity variations are due to an increase in the absorption coefficient, and not to secondary channel related effects.

We employ x-ray spectroscopy to characterize the distribution and magnetism of particular alloy constituents in (Ga,Fe)N films grown by metal organic vapor phase epitaxy. Furthermore, photoelectron microscopy gives direct evidence for the aggregation of Fe ions, leading to the formation of Fe-rich nanoregions adjacent to the samples surface. A sizable x-ray magnetic circular dichroism (XMCD) signal at the Fe L-edges in remanence and at moderate magnetic fields at 300 K links the high temperature ferromagnetism with the Fe(3d) states. The XMCD response at the N K-edge highlights that the N(2p) states carry considerable spin polarization. We conclude that FeN{\delta} nanocrystals, with \delta > 0.25, stabilize the ferromagnetic response of the films., Comment: 4 pages, 3 figures, 1 table

A refined NEXAFS analysis of ethylene physisorbed, chemisorbed and condensed on Cu(100) and Ag(100) will be given. Through deuteration we clearly identify CH and CC vibrations. Applying a simple linear coupling model the Franck-Condon factors for the core excitation process are derived. The only fit parameters are ħω and one single intensity factor S for each vibrational progression, and one linewidth γ for all lines. Form these, we determine the change in bond length for the molecules in the excited state and the decrease of the core hole lifetime upon increasing strength of chemisorption. From the change of the S factors upon chemisorption we determine the force constant that couples the molecule to the substrate. The approach of our analysis will be compared to the recent calculation by Gaeda et al.

We demonstrate geometry-dependent self-absorption effects in the fluorescence yield photoabsorption spectra of bulk NiO. We observe a decrease of the atomic like smooth part of the data above the oxygen K edge and a damping of the EXAFS wiggles. For a cubic substance (NiO single crystal) self-absorption is studied systematically in the energy range above the O K absorption edge by varying the angle between the incident photons and the sample surface over a wide range. If self-absorption is not considered in the data analysis, the amplitudes of the EXAFS modulation can be damped significantly and the errors for coordination numbers can reach 50%.

The Extended X-ray Absorption Fine Structure was measured as a function of temperature above the O K-edge in the O Kα fluorescence yield mode. From the EXAFS amplitude and phase the oxygen atom's local environment could be determined as a function of temperature. These results confirm the changes in frequency and density of A g symmetry vibrational modes observed by Raman spectroscopy. The data are analyzed in terms of a change in the vibrational amplitude of the O2 and O3 versus the Cu2 atoms around T c .

We report L-edge Magnetic Circular X-Ray Dichroism measurements at 30 K of Fe deposited at 100 K on Cu (1 0 0) in the form of ultrathin films and a wedge. The orbital and spin moments of the wedge differ from those obtained for uniform thickness films. For the FCT phase of Fe we stabilised both perpendicular and in-plane easy directions.