Table of contents

Dear participants and other readers of the 12th X-ray Absorption Fine Structure International Conference (XAFS12) proceedings volume. What you are holding in your hands, or reading off your computer screen if you are accessing the electronic version of the proceedings, is the result of a long process. It was initiated in Ako, Japan, already in the summer of 2000 at XAFS11. At that time, Sweden and the Swedish national synchrotron facility, MAX-lab, were chosen to organize the next event in the series of International conferences on x-ray Absorption Fine Structure. After a process of preparations we opened the conference site on the web for electronic submission of abstracts about 6 months before the realization of the event in June 2003. On the way the world had experienced September 11 and a dramatic slowdown in world economics. Given the circumstances at that point we felt uncertain about the possibilities to have a meeting that would reach the size of previous XAFS events. Instead we expected to break the trend of increasing number of participants as documented at previous conferences. Fortunately, we were proven to be wrong.

XAFS-12 was held in late June, 2003 in Malmö, Sweden. More than 450 participants from 30 countries attended the event. The conference accommodated seven plenary lectures, three parallel oral sessions and three poster sessions resulting in some 650 invited and contributed presentations. A breakdown by nation of the submitted contributions is given in Fig. 1 (see pdf file).

Among the plenary events the "Lars Hedin Memorial Session" including the lecture of J. J. Rehr (Seattle, USA) highlighted the importance of the longstanding efforts and successes of the late Lars Hedin and his coworkers at the Department of Theoretical Physics, Lund University, for the theoretical description of excited states. Professor Lars Hedin was a member of the XAFS12 organizing committee before he prematurely passed away.

A wide range of topics and areas were covered at the conference, including XAFS applications to materials science, catalysis and nano-science, biology, chemistry, environmental science, and magnetism. The latest developments in theoretical advances related to XAFS, instrumentation, and novel applications of XAFS were presented. Special sessions were also devoted to related phenomena and emerging techniques. More than 350 papers were eventually submitted to the XAFS-12 proceedings. The number of contributed papers was far greater than expected. A summary of how the contributed papers were divided into categories is given in Fig. 2 (see pdf file). As one might expect, the largest body is found in the rather generic materials category.

It is our view that the XAFS proceedings have a high value for the community and serves as a good indicator of the present trends and developments. It is our opinion that the volume you are accessing is still another convincing example of the power of XAFS based tools using modern light sources. Amongst the contribution you will find many fascinating examples for future trends for the XAFS technique.

Finally, the organizers of XAFS-12 want to gratefully acknowledge the support from the main conference sponsors: the Royal Swedish Academy of Sciences through its Nobel Institute for Physics, the Swedish Foundation for Strategic Research, the Crafoord Foundation, the University of Lund, the Swedish Research Council, the City of Malmö and the Region of Skåne.

We thank all of you for your commitment to this conference and we look forward to another successful gathering of the XAFS-community during the 13th conference in Stanford, California in 2006.

The theory of excited electronic states is central to a quantitative understanding of the interaction between light and matter and hence to calculations of various x-ray and optical spectra. Although ground state properties are well described by density functional theory (DFT), that theory is inappropriate for excited states, for which a fully quantitative theory has yet to be developed. No one has contributed more to than Lars Hedin to the quest for such a theory. Here we briefly review a number of his key contributions. One of the most influential is the "GW" approximation for the self-energy of an excited electron. Another is the "blue-electron" approximation for photon and electron spectroscopies. A third, which is relevant to the topics of this conference, is a many-body theory of x-ray spectra based on the "quasi-boson" approximation. This approach is a generalization of the GW approximation which takes into account both extrinsic and intrinsic losses as well as the interference between them, and simplifies the treatment of losses and the core-hole interaction. What makes Hedin's theories stand out is their mathematical elegance and physical robustness, based on ideas conceived before their full implementation was practical. With today's advances in computational power, however, the impact of Lars' work is becoming ever more widely appreciated.

The theory of x-ray absorption near edge structure (XANES) is complicated due to the difficulty of treating chemical, many-body, and core-hole effects. To address these problems we introduce a full potential, real space Green's function approach for calculations of both local electronic structure and x-ray spectra. Our approach includes inelastic losses as well as screened core-hole and local field effects. The latter are due to the screening of the x-ray electric field. The approach is illustrated in calculations for periodic solids and for small molecules. Calculations for the K-edge absorption of Si crystals show significant improvements in the XANES compared with that calculated with spherical, muffin-tin potentials. However, for systems of high symmetry like the S K-edge in the SF₆ molecule, we find that the nonspherical corrections are small. Instead, local atomic displacements are responsible for additional XANES peaks. Local field effects are shown to be important at the diamond K-edge, which effectively counteract the core-hole interaction.

XRay Absorption Near Edge Structure (XANES) spectroscopy is a powerful method to study the local structure around an absorbing site of various types of matter. Analysis of the spectrum can give both electronic and structural information on the site around the absorbing atom. In this paper we present some recent theoretical advances that allow a complete quantitative analysis of the XANES energy region in term of structural parameters. Some examples will be presented in details with a complete discussion of the strengths and limitations of the method when applied to real systems.

We consider screening of the core-hole potential experienced by the ejected electron in core-excitation processes. This potential affects near-edge structure strongly, but it appears difficult to consistently obtain reliable screened core-hole potentials without substantial computation. Screening effects have both atomic and solid-state (or molecular/cluster) contributions. We emphasize aspects that must be true of "correct" screening models, in an attempt to circumvent the need to carry out full-scale randomphase approximation (RPA) or self-consistent-field calculations of the screening. We present and discuss three spectra computed with RPA and model screened potentials, suggesting ideas to be considered in future work developing screening models.

A many-body relativistic XAFS theory has been developed on the basis of quantum electrodynamic Keldysh Green's function approach. To obtain photon absorption rate we calculate the time derivative of the projected photon Green's function whose self-energy includes relativistic electron Green's functions. For retarded and advanced electron Green's functions we can apply a useful expansion in terms of correlated quasi-nonrelativistic Green's functions.

The combination of x-ray absorption spectroscopy (XAS) with UV-Vis and Raman spectroscopies or with Differential Scanning Calorimetry (DSC) has been recently carried out on the D44 beamline of DCI-LURE. The different set-ups used to perform such combinations are described and examples of combined investigations belonging to different field of materials science (coordination chemistry, sol-gel and catalysis) are presented.

Extended x-ray absorption fine structure (EXAFS) data were measured at three temperatures (20 K, 80 K and 300 K) above the L₃-edge of polycrystalline α-tantalum. The data analysis is based on a recently developed Bayesian approach and uses the FEFF8 code results. Besides the temperature dependence of the lattice constant we obtain a separation of the Debye–Waller parameters into structural and thermal contributions. The latter are well described by a force-field model with two force parameters. A posteriori errors and cross correlations between the model parameters are calculated, taking the errors of the input EXAFS function as well as systematic uncertainties of the model into account. Lattice-dynamical observables determined independently are compared with the results of our force-field model using the parameters from the fit of our EXAFS data.

X-ray Magnetic Circular Dichroism became mature and is used in a large variety of applications. Taking advantage of the element-specificity of XAS, a variety of important problems was addressed: e.g. magnetism and magnetic profiles at interfaces of nanostructures, induced magnetism at chemisorbed molecules, enhanced 2D spin-fluctuations in coupled ultrathin ferromagnet films, the revival of orbital magnetic moments and its relative alignment to the spin moment, limitations for the applicability of the integral XMCD sum rules, separation of dipolar (E1) and quadrupolar (E2) contributions in the XMCD. An equally important progress in the fundamental understanding is the symbiosis of theory and advanced experiments. In all examples given the combination of both was very successful. Theory can "switch on and off" various effects, i.e. L₃-L₂ edges, dipol-quadrupolar effects, layer selective magnetic moments, multiple vs. single scattering. This serves for a better understanding of magnetism on an atomic scale.

Xray Optical Activity (XOA) is caused mainly by E1E2 interference terms in systems with odd space Parity (P). Extra emphasis is put below on nonreciprocal XOA effects in Magneto-Electric (ME) solids in which both Parity and Time-reversal (Θ) symmetries are broken whereas the magnetic structure remains invariant in the product PΘ. Two types of dichroism related to non-reciprocal XOA have been observed experimentally: (i) The x-ray Magnetochiral dichroism (XMχD) detected in the antiferromagnetic (AFM) phase of Cr₂O₃ is associated with the (unpolarized) Stokes component S₀; (ii) A non-reciprocal x-ray Magnetic Linear Dichroism (XMLD) was also observed in the low temperature AFM phase a (V_1−xCr_x)₂O₃ single crystal and is associated with the Stokes components S₁ or S₂. Edge selective XOA sum rules were derived recently which give a unique access to a whole family of spherical ME operators mixing orbitals of different parities in what is assumed to be the ground state. It is proved that the orbital anapole moment Ω₀⁽¹⁾ is primarily responsible for the XMχD signal measured both with a single crystal or a powdered sample of Cr₂O₃. It is suggested that the nonreciprocal XOA in both Cr₂O₃ and (V_1−xCr_x)₂O₃ is due to partially unquenched angular moments that had a different quantization axis from the spins.

This paper reviews our recent study on the improvement of time-resolved energy-dispersive x-ray absorption fine structure (DXAFS) and its application to in situ dynamic characterization for structural changes in nano-structures and catalysts, also presenting new data. The issue addressed in this paper is relevant to deeper understanding of catalytic intermediate structures, elementary steps, and reaction mechanisms.

Time-resolved x-ray absorption spectroscopy (TR-XAS) possesses excellent capabilities to reveal quantitative phase composition and average valence together with the evolution of the local structure of a system under dynamic reaction conditions. The work discussed here focused on time-resolved in situ XAS investigations aiming, first, at understanding structural evolution under dynamic conditions and, second, at revealing properties of the system studied not available from investigations under stationary conditions. In order to demonstrate the potential of TR-XAS in heterogeneous catalysis, TR-XAS investigations combined with mass spectrometry of the structural evolution of Keggin type heteropolyoxomolybdates (HPOM) during thermal treatment in propene and in propene and oxygen in the temperature range from 300 K to 773 K are presented. It is concluded, that the undistorted Keggin ion in the as-prepared HPOM has to be regarded as a precursor of the active catalyst, while the formation of lacunary Keggin ions is a prerequisite for catalytic activity.

Energy dispersive EXAFS (EDE), using a Laue monochromator on ID24 of the ESRF, and multiple ion monitoring mass spectrometry have been used to monitor the structure and function of alumina-supported rhodium and palladium catalysts within a microreactor. Metallic 5%-Rh/Al₂O₃ was preformed in situ by hydrogen reduction, and shown to react rapidly with NO at room temperature yielding an oxidised phase. In order for this material to catalyse the reduction of NO by H₂ (to N₂), it was shown that the metallic phase must be reformed. The "light-off" temperature at which the metallic phase was formed and catalysis commenced varied with NO : H₂ stoichiometry, this temperature lowering in more reducing conditions. N₂O formation was concomitant with the conversion from the oxidised to the metallic phase.

The EDE configuration allowed the simultaneous monitoring of structure at both the rhodium and palladium K-edges. Incorporation of a 20% palladium mole fraction into 5%-Rh-Pd/Al₂O₃ protected rhodium from oxidation and also reduced the light-off temperature, and this is reflected in low coordination number values for the composite Pd to Rh/Pd shell. This favours palladium being preferentially on the surface of the nanoparticles. At higher temperatures there are changes in coordination numbers than imply a redistribution of metal sites under catalytic conditions. Future plans to include infrared spectroscopy as a third simultaneous technique will be outlined.

Zeolites are used for a wide variety of reactions, such as cracking and isomerization of alkanes, and for the production of fine-chemicals. Although these catalytic systems are extensively studied, very often structure–activity relations are lacking. Relevant techniques that determine the catalyst structure under catalytic conditions are limited. In many reactions, the aluminum atom is associated with catalytic activity, making an experimental tool that detects the aluminum coordination in a controlled atmosphere extremely valuable. Conventional methods often fail in providing such data.

Developments in instrumentation and data-interpretation enable measurements in controlled gas-atmosphere at elevated temperature at the Al K edge. A thorough theoretical interpretation of the XANES spectra using FEFF8 enables assignment of different aluminum coordinations in the samples. The measurements on zeolitic samples have shown that the aluminum coordination is a subtle function of the precise measurement conditions, which has consequences for interpretation of catalytic data. Moreover, measurements at extreme high temperature show the appearance of unique spectral features that can be attributed to a unique aluminum coordination previously not observed using ex-situ techniques.

During the past decade, applications of synchrotron radiation (SR) methods to environmental science have grown significantly, resulting in a new interdisciplinary field known as molecular environmental science, which focuses on the molecular-level speciation of environmental pollutants and the fundamental chemical and biological processes determining their behavior in complex systems. Here we review some recent applications of XAFS spectroscopy and related SR methods, including micro-XANES and X-ray Standing Wave (XSW) spectroscopy, micro-XRD, x-ray fluorescence micro-tomography, and photoemission spectroscopy to heavy metals and actinides in model systems and more complex environmental samples. Examples include XAFS studies of heavy metals and actinides at environmental interfaces, combined XAFS and XSW studies of heavy metal interactions with microbial biofilm-coated metal oxide surfaces, and combined XANES and photoemission studies of microbial interactions with metal sulfide surfaces.

We have recently developed a new type of near-edge x-ray absorption fine structure (NEXAFS) technique, "dispersive-NEXAFS" by using energy-dispersed x-rays and a position-sensitive electron-energy analyzer. With this technique a NEXAFS spectrum is taken in a one-shot manner without scanning photon energy resulting in a typical data acquisition time of several tens seconds. This enables to monitor the dynamic surface processes such as film growth and surface reaction. As examples of such applications, we present kinetics studies of catalytic oxidation reactions on the platinum (111) surfaces. Future possible improvements of this technique are also addressed.

The timing structure and the high photon flux of x-ray pulses from the Advanced Photon Source permit pump-probe techniques widely used in ultrafast laser spectroscopy to be extended into the x-ray regime. The intrinsic time resolution of the experiments is determined by the FWHM of the single pulses from the synchrotron at 70–100 ps. The challenges and the solutions in such experiments will be discussed. Using laser pulse pump, x-ray pulse probe XAFS, several excited state molecular structures in solutions were studied. We will mainly describe molecular structures of the photoexcited metal-to-ligand-charge-transfer state of [Cu^I(dmp)₂]⁺, where dmp is 2,9-dimethyl-1,10-phenanthroline, in toluene and acetonitrile. The experimental results indicated that the copper ion in the thermally equilibrated MLCT state in both solvents had the same oxidation state as the corresponding Cu(II) complex in the ground state and was found to be penta-coordinate with an average nearest neighbor Cu–N distances 0.04 Å longer in toluene and 0.04 Å shorter in acetonitrile than that of the ground state [Cu^I(dmp)₂]⁺. The results further revealed that what distinguishes the MLCT state structures in non-coordinating and coordinating solvents is not the "exciplex" formation, but the strength of the interactions between the solvent and the Cu(II)* species at the MLCT state. In addition, future direction of time-resolved XAFS will be discussed.

For local structure and electronic state analyses of electron trapping centers, we developed a site-selective x-ray absorption fine structure XAFS measurement, i.e., the capacitance XAFS method. The concept of the capacitance XAFS measurement is based on the fact that the x-ray absorption of trapping centers, not the bulk, can be evaluated from the capacitance change due to x-ray induced photoemission of a localized electron. With this method, micro spectroscopy can be achieved by scanning probe detection of the capacitance. Moreover, trapping centers with a specific eigen-energy can be selectively observed by controlling the sample bias voltage. We tested these advantages in detail for two typical metal and semiconductor systems. (1) The capacitance XAFS spectrum of Cu indicated twodimensional (2D) electronic states at a hetero interface between native oxide (Cu₂O) and bulk Cu; the Cu 4pπ states of the electron trap were confined into a 2D plane. (2) The capacitance XAFS spectrum of GaAs depends on the sample bias voltage and on selectively indicated electronic states of surface trapping center due to Ga oxide, which captures electrons at a positive bias voltage.

We describe an experimental setup, which measures transient chemical changes of photoexcited solutes in disordered systems via time-resolved X-ray Absorption Spectroscopy (XAS) with picosecond temporal resolution. The setup combines a femtosecond amplified laser with picosecond x-ray pulses at beamline 5.3.1 at the Advanced Light Source in Berkeley, USA. New results on time-resolved XAS used for probing both the electronic and the geometric modifications of a photoexcited tris-(2,2'-bipyridine) ruthenium (II), [Ru^II(bpy)₃]²⁺ in water solution are presented.

In-situ x-ray absorption spectroscopy (XAS) was used to probe the local structure of photo-induced phase of Fe(II) spin-crossover complex. High-quality XAS data under photo-excitation were obtained for fine powder specimen using a novel pixel array detector (PAD). It was demonstrated that the technique can x-ray probe opaque specimen with high sensitivity (requiring less than 10⁻³ g) which is irradiated with visible photons. We find that the nearly octahedral ligand coordination (O_h) of FeN₆ cluster undergoes a significant expansion upon the diamagnetic (S = 0) ↔ paramagnetic (S = 2) transformation induced by laser light (532 nm), at much lower temperature than the critical temperature of thermally induced phase transition. Indication of symmetry breaking was observed in the distorted ligand molecules, in contrast to the relaxed undistorted structure in the thermally induced high spin phase.

Magnetic structure and L_2,3 edge x-ray magnetic circular dichroism (XMCD) spectra of free spherical iron clusters containing 9–89 atoms are calculated employing the ab-initio fully-relativistic spin-polarized multiple-scattering method. The average spin m_spin and orbital m_orb magnetic moments as well as their ratio m_orb/m_spin are larger in clusters than in the bulk, with the ratio m_orb/m_spin approaching the bulk values more rapidly than either m_spin or m_orb. Theoretical XMCD spectra of free clusters differ from their bulk counterpart mainly through smaller widths and sharper maxima of the main peaks. A small yet distinct feature just above the main L₃ edge peak appears for all the investigated clusters and could thus serve as a marker of clusterization.

X-ray magnetic circular dichroism (XMCD) at the rare-earth (RE) L_2,3 absorption edges of RFe₂ (R = RE) in the Laves phase has been investigated based on the tight-binding model with the intra-atomic exchange interaction between 5d and 4f electrons. We find that the magnetic polarization of 5d electrons, being essential for these XMCD, is dominated by the intra-atomic exchange interaction and by the hybridization with spin-polarized Fe 3d states. These contributions as well as the quadrupole one compete, resulting in a variety of XMCD spectra, as observed in experiments.

The analysis of EXAFS and XANES spectra of aqueous solutions and hexane extracts shows the interaction between hydrated (or solvated by (Oct)₃PO molecules) Cu²⁺ cations and the complex anion [Ru(NO₂)₄(NO)(OH)]^2-. This interaction is accompanied by the increase of the interatomic distances Ru–O from 1.96 to 1.99 Å in the first coordination sphere of Ru atoms. The average interatomic Ru–Cu distances of the resulting heterometallic complexes have been estimated as 3.4 Å. The bond between Ru- and Cu- fragments of heterometallic complexes in their extracts with (Oct)₃PO in hexane is most probably carried out via oxygen atoms of OH and NO fragments of NO₂ group of complex anion.

Many-electron (correlation) effects play a dominant role in inner-shell ionization processes in free alkaline earth metal atoms. In this work calcium 2p, strontium 3d and barium 4d photoionization processes have been investigated with emphasis on the correlation effects. In order to understand the details of the spectra, a series of ab initio calculations based on multiconfiguration Dirac–Fock method have been performed. Theoretical predictions are compared with high-resolution synchrotron radiation induced electron spectra and the capability of the multiconfigurational computations in reproducing the experiment is discussed.

We report a theoretical study of core-level x-ray photoemission (XPS), x-ray absorption (XAS) and resonant x-ray emission spectra (RXES) at Mn L_2,3 edge in Mn thin films on Ag(001). By combining band structure, atomic multiplet and impurity Anderson model calculation, we construct a realistic impurity model that includes full intra-atomic multiplet interaction and inter-atomic coupling to the Mn-3d and Ag-4d bands. The model is applied to various Mn/Ag thin films and related structures. The different systems were modeled by varying only one parameter, the hybridization strength. Good agreement with experiment is obtained. The main conclusion from the impurity model calculations is that the satellite structure observed in the thin films is due to final state charge transfer process, mainly from the Mn-3d states of the neighboring atom. Moreover we predict that the RXES spectra have a satellite structure which is highly sensitive to the local atomic structure around the Mn atoms through its strong dependence on the hybridization of the Mn-3d orbitals.

The probabilities of non–monopole processes of additional electron excitation / ejection conjugate shake up/off processes upon 2p–photoionization of atomic sulphur are calculated in the frame of first–order perturbation theory for the wavefunctions. Both conjugate shake up and conjugate shake off processes are important on a comparatively wide energy scale, and they may cause noticeable discontinuities in atomic photoabsorption.

The (010) surface of vanadium pentoxide, V₂O₅, contains 1-, 2-, and 3-fold coordinated oxygen centers which can participate as active sites in specific surface reactions. In the present work we use ab initio density functional theory DFT together with cluster models to calculate 1s core excitation spectra of the different oxygen centers. Excitation energies and intensities are characterized by details of local V–O binding where the data depend strongly on coordination. As a result, strong coordination dependence of the angle-resolved NEXAFS spectra of different oxygen centers is found. The differences can also be seen in the total spectrum obtained from a superposition of the atom specific spectra. A comparison of our theoretical spectra with experimental NEXAFS data yields good agreement and allows an assignment of the experimental peaks to the differently coordinated oxygen centers.

We present a reciprocal-space "non muffin-tin" scheme for calculating X-ray Absorption Near-Edge Structure (XANES). The method uses pseudopotentials and reconstructs all electron wave functions within the Projector Augmented Wave framework. The method incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole-electron interaction through large supercells (hundreds of atoms). This opens new fields of applications like surfaces, molecules, small aggregates or amorphous materials, for which large supercells are required. The method is applied to the natural linear dichroism at the Al K-edge in corundum (α-Al₂O₃). Details about the convergence process of the calculation are given. The influence of the core-hole effects is emphasized and comparison with "muffin-tin" multiple scattering calculation is made.

We have studied the performance of the non local optical potential as developed by Fujikawa, Hatada and Hedin [Phys. Rev. B 62, 5387 (2000)] along the lines of the GW approximation for the photoelectron self-energy, in the case of the absorption spectrum of nickel hydrate (Ni(OH₂)₆). Comparison with the local Hedin-Lundqvist potential [J. Phys. C 4, 2064 (1971)] shows a substantial improvement especially in the low energy region of the spectrum.

We have investigated the feasibility of an ab initio polyatomic R-matrix/MQDT (multichannel quantum defect theory) method using Gaussian type basis functions for bound and continuum states to analyze the near edge feature of molecules. Test molecules here are N₂, C₂H₂, and NO. The R-matrix/MQDT method is revealed to be indispensable for the Rydberg states with higher quantum numbers and continuum states, none of which can be described by using Gaussian type functions in the outer region from an appropriate boundary. The close-coupling calculation augmented with the correlation term, which is carried out for the inner region, is powerful to describe the valence states and the interchannel coupling in several core-ionized states.

The local structure of dilute Ge impurity in Si thin film has been studied by grazing incidence fluorescence XAFS in the temperature region of 20 ∼ 300 K. Multiple-scattering XAFS (MS-XAFS) data analysis is used to fit the local structures around Ge atoms from the first to third coordination shells for the Ge_0.006Si_0.994 thin film. The results indicate that the bond length R_Ge–Si of the first, second and third Ge-Si shell is 2.38, 3.83 and 4.49 Å for the Ge_0.006Si_0.994 thin film, respectively. The R_Ge–Si of the first Ge–Si shell in the Ge_0.006Si_0.994 thin film is 0.03 larger than that of the first Si–Si shell in Si crystal, and the R_Ge–Si of the second and third Ge–Si shells in the Ge_0.006Si_0.994 thin film are almost equal to those of the corresponding Si–Si shells in Si crystal. These results imply that the local lattice deformation exists in the first nearest neighbor around Ge atoms and the lattice distortion relieves in the second and third Ge–Si shells for the Ge_0.006Si_0.994 thin film. Furthermore, the results show that the Debye-Waller factor σ₁² of the first Ge–Si shell of the Ge_0.006Si_0.994 thin film increases slightly from 0.0018 to 0.0020 Å² in the temperature region between 20 and 100 K, and rises strongly to 0.0040 Å² at 300 K. The bond angles θ_Ge–Si–Si at all temperatures are about 108.1°, which is close to the value of tetragonal network of 109.47°. The bond angle variation Δθ_Ge–Si–Si is about ±3.4°, ±3.5° and ±5.0° at the temperatures of 20, 100 and 300 K, respectively, indicating a weak tetragonal distortion around the Ge atoms in the Ge_0.006Si_0.994 thin film.

EXAFS measures the thermal variation of average interatomic distances, while Bragg diffraction and dilatometric techniques measure the variation of distances between average atomic positions. The difference not only gives information on vibrational motion perpendicular to the bond direction, but can be exploited to study the local behaviour in systems affected by negative thermal expansion. Recent results on copper, germanium and Ag₂O are presented and critically compared.

We present a multichannel extension of the multiple scattering method for x-ray absorption fine structure (XAFS) spectroscopy that allows to take account of atomic multiplet-like electron correlation effects in condensed systems, on the basis of ab initio electron structure calculations. The formalism is outlined and an application to near-edge XAFS at the L_2,3 edges of Ca metal is presented. In this system, the experimentally observed branching ratio deviates strongly from that obtained from the standard (one-electron) approach to XAFS. This is due to that fact that one-electron theory neglects the multiplet coupling between the photo-electron and the 2p core-hole. Within the multi-channel method, this correlation effect can easily be taken into account and the calculated spectrum agrees well with experiment.

The sensitivity of x-ray absorption spectroscopy (XAS) to the local structure around a selected atomic species symmetry, distances and angles is commonly exploited to quantitatively describe systems where all the configurations around the absorbing atoms may be approximated by the mean one. However, in many cases of disordered systems a simple description of the local structure with single-configuration models cannot be reconciled with experimental spectra.

In this paper the necessity to analyse the XAS spectra by considering a multiplicity of atomic structural configurations is demonstrated in the case of silver borate glasses.

The local coordination around Ag cations in (Ag₂O.nB₂O₃) glasses has been studied by comparing the XAS experimental spectra at the Ag K edge with theoretical XANES and EXAFS spectra obtained by a configurational average of model structures.

In order to provide a reasonable agreement with experiment, these models have to take into account that there are many geometrically distinct Ag neighbourhoods present in the system, and that the measured XANES and EXAFS signals are in fact averages over spectra originated at all the non-equivalent photoabsorbing sites (multi-configuration approach).

In this paper we present a detailed quantitative analysis of the iron K-edge XANES data of potassium ferrocyanide in water solution. The right structural determination as been obtained from the XANES data by using the MXAN procedure to fit the experimental data despite the presence of small discrepancies between experimental data and best-fit calculations at low energy. The origin of such discrepancies is also discussed in terms of non muffin-tin corrections and the role of the right charge density of the cluster.

Approximations in the treatment of Debye–Waller factors in multiple scattering calculations are one of the principal remaining uncertainties in XAFS calculations. The amplitude of each path varies as a function of the mean square variation in path length. This quantity depends on the many-body correlations involving atoms in the path, as well as the mean square displacement of individual atoms. The correlations normal as well as parallel to interatomic vectors are required, and the effects of anharmonicity must be taken into account. Although difficult to calculate accurately, these quantities can be extracted directly from molecular dynamics (MD) simulations. Here we present temperature dependent results for copper, using a semiempirical potential based on a tight-binding model, from which the cumulants of the variation in path length as well as the correlation functions are derived. XAFS calculations based on extracted parameters are compared with those calculated directly from the MD atomic coordinates, and with results using Debye model and lattice dynamic calculations.

The Bond Valence model gives a simple, accurate relationship between the bond distance, co-ordination number, and formal valence of ions in many systems. This empirical model thus gives complementary information to EXAFS and XANES, and has been used as an independent check of XAFS results by many workers. More generally, the Bond Valence represents prior knowledge of the system that can be used to constrain the XAFS analysis itself. Since Bond Valence sums are not perfectly satisfied, their use as exact constraints in XAFS analysis may not be warranted and they are probably best suited as restraints – inexact conditions placed on the analysis that act as additional data or prior knowledge of the system. The practical use of Bond Valence sums as constraints and restraints in EXAFS analysis is demonstrated for iron oxides, and the use of Bond Valence sums as prior knowledge that can be applied to a wide-range of XAFS analyses is discussed.

The complicated as to their composition and crystal structure semiconductors TlAsS₂, Tl₃AsS₃, Tl₃AsS₄, called briefly TAS, and Tl₃PS₄ represent a class of compounds promising in the devices of quantum electronics. The electron energy structure of these compounds is investigated both experimentally with x-ray spectroscopy and theoretically by calculations of the local partial electron densities of states (LDOS) and x-ray K-absorption spectra of S and P using FEFF8 code. All theoretical K-absorption spectra and LDOS were calculated ab initio without any adjusting parameters according to the scheme: the self-consistent mt-potentials obtained for the clusters of about 35 atoms were then used in the calculations of the absorption spectra and LDOS for clusters of 87 atoms in the full multiple scattering approximation. The comparison of the calculated K-absorption spectra of S and P of sulfides investigated with their experimental analogues shows that in all cases the theoretical curve reflects good enough the energy positions of all features of the experimental curve. The results of the calculations of LDOS and the experimental emission K- and L_2,3-spectra of S and P gave the possibility to determine the energy positions of the electron occupied states of all elements in the semiconductors TAS and Tl₃PS₄ and to get the information about the hybridization of the electron states in the valence band. The compounds Tl₃AsS₃ and Tl₃AsS₄ have the same crystal structure, this leads to the likeness of their K-absorption spectrum of S and the electron energy structure of their valence bands.

Sodium K edge XANES calculations were performed for sodium halides, using the last version of the ab-initio FEFF code, and compared with the experimental data. Several FEFF parameters were varied during calculations, aiming to investigate their influence on the theoretical results. The origin of the differences between the experimental data of the series are analyzed and discussed, supported by the theoretical calculation.

The structural parameters of Ti coordination environment in glassy titanite (CaTiSiO₅), natisite (Na₂TiSiO₅) and radiation damaged CaTiSiO₅ are determined by the method proposed earlier, based on the Fourier-transform analysis of Ti K-XANES over the short k-range of photoelectrons wave numbers. The accuracy of the determined parameters is tested for the model crystals CaTiSiO₅, Na₂TiSiO₅. The modelling of the extracted contribution into Ti-XANES, arising from the oxygen-polyhedron around the ionised Ti atom in amorphous titanites and natisite, performed via the single-shell fit and the two-shells fit, returns not only the averaged structural parameters, but also reveals the main groups of the Ti–O distances for this polyhedron.

We present the Al Kedge XANES spectrum of synthetic mica with mixed fourfold coordinated and sixfold coordinated Al (preiswerkite). Experimental analysis and multiple scattering simulations of XANES spectra demonstrate that octahedral contributions may overlap the tetrahedral ones so that the lower energy structures in mixed coordination compounds may be associated to Al octahedral site. This unexpected behavior can be explained as due to a large local distortion of the Al octahedral site.

The mean square variation of the halfscattering path length in x-ray absorption fine structure Debye–Waller factors has been expressed as a function of the first shell radial distance and an angle (where applicable) for Zn⁺² active sites of metalloproteins enabling direct and accurate calculation of the single and multiple scattering Debye–Waller factors at arbitrary temperatures. The local character of the filled d-orbital Zn⁺² element does not obstruct us from extending this technique to other metals with unfilled d-orbital. In this report we present initial results based on one-dimensional radial models applicable to the d⁹ Cu(I) and Cu(II) histidine/imidazole and cystein complexes. Results from these new models are compared with large reference structures of homogeneous and heterogeneous Cu metal ligation built and optimized by non-local Density Functional Theory.

K-edge XANES spectra of CuGaSe₂, ZnGeAs₂ and CuFeS₂ are studied both experimentally and theoretically. While spectra of CuGaSe₂ and ZnGeAs₂ are remarkably similar, spectra of CuFeS₂ differ significantly, especially in the pre-edge region. Full-potential band structure calculations without any core hole give essentially the same results as real-space multiple-scattering calculations for a muffin-tin potential with a core hole included the notable exception is the Cu edge in CuGaSe₂, where non-muffin-tin effects possibly occur. The distinct pre-peak visible at all three spectra of CuFeS₂ arises from transitions to delocalized multiple-scattering resonances which are confined almost exclusively to the Fe sites.

The hole doping effects on the O 1s x-ray absorption spectrum (XAS) of a quasi-one-dimensional charge-transfer insulator, Ca_2+xY_2−xCu₅O₁₀, are discussed on the basis of numerically-exact diagonalization calculations applied to finite-size cluster models. The angle-resolved photoemission and inverse one are also calculated to understand the characteristic features in the XAS. The role of "edge-share"-type crystal structure, as well as that of electron correlation, is emphasized to understand the localized nature of the electronic states. The dp model Hamiltonian used in the O 1s XAS calculation can be mapped onto a single-band Hubbard model with the intra-atomic Coulomb repulsion, U, and the first and second neighbor hoppings, t₁ and t₂ (t₁ ≈ t₂).

This paper describes a Path Integral approach to the thermal factor in EXAFS applied to one-dimensional systems with asymmetric double-well potentials, which is considered to be one of the models for chemical reactions, structual phase transitions and surfaces within of the clusters. For these systems quantum-tunneling effect plays an important role in both amplitude and phase of the EXAFS thermal factor. Classical approximation is not valid in the low temperature region, on the other hand cumulant expansion breaks at high temperature. We find an oscillating behavior in the phase of the thermal damping function, which is a specific feature for the case of asymmetric double-well potential.

A new scheme of capacitance-detection for the x-ray absorption fine structure (XAFS) was reported recently [M. Ishii, Phys. Rev. B 65, 085310 (2002)]. The absorption of x-rays leads to oscillations in the steady state capacitance of a Schottky barrier diode which were interpreted as a site-selective detection of deep level centers. We have performed XAFS at the K-edge of gallium and arsenic on GaAs and AlGaAs Schottky-diodes containing DX and EL2 defect centers. For the detection, different techniques were applied: the photocurrent under short circuit conditions, the steady state impedance, and x-ray induced capacitance transients were measured. The results are compared with conventionally detected XAFS spectra (absorption, fluorescence). No evidence for a site-selectivity of the capacitance EXAFS is found in our studies. Based on a detailed analysis of the different detection techniques we strongly question the proposed "site-selectivity".

The red color of ruby (α-Al₂O₃:Cr³⁺) is assigned to transitions between 3d states of the chromium ion. A precise description of the structural and electronic environment of the Cr³⁺ ion in its slightly distorted octahedral site (C₃ symmetry) is needed to understand the cause of the color. We have analysed the Cr K-edge in Cr³⁺ with a reciprocal space approach that allows the computation of self-consistent spin polarized charge density for large unit cells, beyond the traditional "muffin-tin" approximation. Structural and electronic information is deduced from the calculation.

L XAFS spectra of polycrystalline Fe and Cr films are investigated by EXAFS and TEY (Total Electron Yield) techniques. A new method of obtaining local structure information from overlapping L XAFS spectra for 3d metals is proposed. Tikhonov regularization method of solving ill-posed problem is used. In contrast to the conventional methods (Fourier transformation and fitting procedures) this method does not demand any model assumption and any special procedure of deconvolution of L₁ –, L₂ –, L₃ – contributions. The parameters obtained from L XAFS spectra of polycrystalline Fe and Cr films (interatomic distance and coordination number for the first and the second coordination shells) agree with the expected crystallographic values. Up to now the regularization method was applied only to nonoverlapping XAFS spectra.

In many cases x-ray absorption spectra measured in transmission mode are degraded by an inhomogeneity in thickness of the samples. As a result, the EXAFS amplitude is decreased and information about the coordination numbers is distorted. To avoid this influence, it is necessary to prepare a homogeneous sample. But, for powder samples, thick inhomogeneous foils, and sputtered films this is not possible. Absorption spectra on these samples should be corrected for the thickness inhomogeneity effect.To correct an absorption spectrum it is necessary to know the sample thickness distribution function. We propose a method of solving an integral equation for a distribution function as an inverse problem. We use and compare the experimental pre-edge absorption behaviour with the theoretical Victoreen function. We apply the Tikhonov regularization algorithm to determine the distribution function. Model calculations are carried out to check the reproducibility of the calculations. This method is applied to preliminary procession of x-ray absorption spectra for high quality foils of crystalline Cu, crystalline Cu powder samples, and an inhomogeneous foil of ordered Ni₅₀Mn₅₀ alloy. We estimate the thickness inhomogeneity effect on the coordination numbers in the cases before and after correcting the spectra.

We propose the chemical matched EXAFS regularization method through the numerical analysis of Mn Kedge EXAFS data for La_1−xCa_xMnO₃ specimens. A relatively narrow k-space window (k_max − k_min = 6 Å⁻¹) has been used to compute the Mn–O pair distribution function in the specific r-space range of 1.8–2.2 Å. Results show that the resolution in r-space is greatly improved in the pair distribution functions of the Mn–O bond. EXAFS data of specimens with double shell pair distributions were hardly analyzed by the conventional method because they are not resolved in the Fourier transform. A preliminary test of the EXAFS regularization method shows that this is very effective method to study the double shell distribution due to the Jahn Teller effect. The test was performed on La_1−xCa_xMnO₃ at x = 0.2 and 0.3.

Extended x-ray absorption fine-structure (EXAFS) data collected in the fluorescence mode are susceptible to an apparent amplitude reduction due to the self-absorption of the fluorescing photon by the sample before it reaches a detector. Previous treatments have made the simplifying assumption that the effect of the EXAFS on the correction term is negligible, and that the samples are in the thick limit. We present a nearly exact treatment that can be applied for any sample thickness or concentration, and retains the EXAFS oscillations in the correction term.

Today a lot of XAFS analysis software is available either free of charge, licensed or commercially. The list of the programs can be found on web sites (IXS web site displays 35 programs and ESRF web site displays 23) and there are many XAFS analysis softwares not on such lists yet. We describe recent progress of the latest version of the REX2000 XAFS analysis package. The REX2000 runs on MS-Windows family operating system, and is an entirely new package with a user-friendly interface and simple operation. The package provides many classic DATA reduction methods for EXAFS and XANES. All the parameters needed for DATA analysis can be set on graphics windows as well as numerical input. The package also has FEFF interface for multiple scattering capability.

The independent-electron approximation together with the final-state rule provides a well established method for calculating x-ray absorption spectra that takes into account both core-hole effects and inelastic losses. Recently a Bethe-Salpeter Equation approach based on Hedin's GW approximation that explicitly treats particle-hole excitations has been applied to the same problem. We discuss here the formal relationships between these approaches for deep-core x-ray spectra and show that they are similar, apart from differences in their practical implementations. Their similarity is illustrated with results from both theoretical approaches and compared with experiment. This comparison also suggests ways to improve both approaches.

The solid solutions Cu_xAg_1−xGaS₂ and Cu_xAg_1−xInSe₂ for x = 0.5 and their terminal compounds (x = 0; 1) have been investigated both theoretically and experimentally using x-ray emission and absorption spectroscopy. These solid solutions are advanced materials for the transformation of solar energy. The electron structure of these solutions and compounds was investigated using FEFF8 code. The calculated local densities of electron states and x-ray absorption spectra were compared with our experimental x-ray spectra and photoelectron curves taken from the literature. The good correspondence of the theory to the experiment guarantees the assumed interpretation of the results for the solid solutions Cu_xAg_1−xGaS₂ and Cu_xAg_1−xInSe₂. It was found that in these solid solutions "pushing apart" of d-states of Cu and Ag takes place, which can be explained by the splitting of p-states of the atoms C^VI and d-states of A^I-atom (Cu and Ag). Our calculations have proved and explained the nonlinear dependence of the energy gap E_g on x.

The Fe-O distances (R₁) and the number of nearest oxygen atoms (N₁), which coordinate Fe in Fe(II) and Fe(III) containing silicate glasses are determined by the method based on the Fourier-transform analysis of XANES performed for the short k-range and the subsequent fit of the extracted first shell's contribution. The scattering amplitudes for Fe-O pair, used for the fit, are calculated by the HF MT-potential with the neutral electronic configurations of atoms. The validity of this model for the different redox states of Fe in glasses and the accuracy of the determined (R₁) and (N₁) are analyzed applying the method to the Fe K-XANES of the references – Fe(II) and Fe(III) aqueous sulfate solutions. The modeling of the contribution of the Fe nearest oxygens to the Fe KXANES of Fe(II)- and Fe(III)-rich silicate glasses, as well as in the series of glasses with the mixture of Fe(II) and Fe(III) states, performed through a single-shell fit and a subsequent two-shell fit, provides structural parameters for the oxygen-polyhedron around the ionized Fe²⁺ and Fe³⁺ atoms and gives access to the estimates for the Fe²⁺/Fe³⁺ ratio changes among all samples studied.

In the room-temperature EXAFS spectrum of Rb in the Rb/K alloy, the sharp spectral features due to double photoexcitation are plainly visible from 40 eV above the K edge. The weak and short structural signal is attributed to the strong thermal disorder. A unique atomic absorption background of the Rb atoms in the solid alloy is extracted and compared to the pure atomic absorption, measured on the monatomic Rb vapor, as a direct test of the practical transferability of experimentally determined atomic absorption backgrounds.

The continuous Cauchy wavelet transform (CCWT) is applied to the analysis of XAFS spectra. Thanks to that method, XANES and EXAFS signals can be visualized in three-dimensions: the wavevector (k), the interatomic distance uncorrected for phase-shifts (R') and the CCWT modulus (corresponding to the continuous decomposition of the amplitude terms). Applied to EXAFS spectra, the CCWT analysis provides straightforward qualitative information related to the k-range of each "R'-EXAFS" contribution. Such information is particularly useful to perform next nearest-neighbors identification, despite the presence of spectral artifacts such as multiple-scattering features, multi-electronic excitations or noise. When applied to XANES spectra, the CCWT analysis helps highly to measure the "spectral limit" between XANES and EXAFS regions, as well as the energy range required to model properly next-nearest neighbors. To further illustrate the potential of CCWT analyses applied to XAFS spectra, we present examples related to: (1) a XANES spectrum collected at the Ti K-edge for titanite (CaTiSiO₅); (2) an experimental Au L_III-edge EXAFS spectrum for gold sorbed on goethite (FeO(OH)).

Pre-edge features in the Ni K-edge x-ray absorption nearedge structure (XANES) spectrum of Ni monoxide (NiO) in octahedral coordination, were investigated. By comparing experimental data with dipolar and quadrupolar cross-section calculations in the framework of the full multiple-scattering theory we assign the first pre-edge peak to a direct quadrupolar transitions from the 1s core state to the 3d molecular orbitals of the central atom (due to the more effective attraction of the core hole). The intensity of quadrupolar transition is almost equal to the dipolar pre-edge structure, at higher energy, due to the hybridization between the p-orbitals of the central atom with the higher-shell metal octahedral orbitals, that reflects the density of states derived by the medium range order of the system.

This report describes an effort to include threedimensional interactive molecular graphics into the main APEX program, a free, open source, cross platform data analysis package for XRay Absorption Fine Structure (XAFS) data analysis. The latest version of APEX (2.7.3) based on a native TCL/TK tab-notebook style graphical user interface includes among others, user-friendly interactive two-dimensional graphics under BLT, an extension of TCL/TK with advanced printing capabilities; generic format conversion from ASCII to University of Washington binary-type files; new TCL routines for data handling; XMU corrections and multiple scattering fitting. Based on Virtual Rendering System (VRS), the 3D version reads and displays molecular structures for various file formats allowing object rotation, translation and atoms selection for determining interatomic distances and angles. The most important feature of 3D APEX is the interaction with the FEFF program: scattering paths are displayed, selected and are used to generate appropriate χ(k) XAFS spectra. 3D APEX is the only program that offers three-dimensional graphics and in its current form is suitable for routine data analysis and training. At this time the 3D APEX add-on is only available for Windows PC. Addition of more advanced methods of data analysis are planned.

Electronic decay of synchrotron-radiation-excited VUV-resonances in the KCl and CsCl molecules is studied. Despite the similarity of the two compounds, qualitatively different resonant modifications of the valence electron spectra are observed and are investigated by modelling nuclear dynamics including the lifetime vibrational interference. The modelling predicts a much shorter lifetime of the resonances in KCl than in CsCl, which is confirmed by ion yield measurements as due to the opening of a spectator-type decay channel in KCl.

Extended x-ray absorption fine structure data evaluation usually begins with the Fourier transform of the spectrum. We suggest the wavelet transform as a complement to the Fourier transform. While the Fourier transform analyzes the distances to the backscattering atoms, wavelet transform additionally reveals the wavenumber dependence of the scattering. Thus wavelet analysis can differentiate between heavier and lighter backscattering atoms, even if they are almost equidistant from the central atom. First the method of operation and the advantage of the wavelet analysis will be demonstrated by simple models. Then it is applied to the interpretation of extended x-ray absorption fine structure spectra concerning the complexation of Uranium(VI) with the carboxylic groups acetic-, formic-, and glycolic acid. The wavelet transform analysis suggests clearly for the system Uranium-formic acid both, U-U and U-C-C, structural elements. In contrast to the clear separation of different scattering paths by wavelet transform, Fourier transform analysis was not able to resolve the two different backscattering processes.

X-ray absorption coefficient of Cs in the energy region of L edges has been measured on a 1:9 alloy of Cs and Na at room temperature. The absorption spectrum is virtually free of the structural signal. EXAFS oscillations are visible only in a ∼70 eV wide interval immediately above the edges. The short range of the signal is attributed to a strong disorder of the alloy introduced by the complete miscibility of the constituents and the large difference of their metal radii. The spectral regions above three L-edges exhibit the same pattern of sharp multielectron photoexcitation features involving electrons from outer subshells 6s to 4p as in the adjacent element xenon. The segment above the L₃ edge can be used as the atomic absorption background for the standard EXAFS structural analysis of Cs compounds.

This paper presents a method for choosing the optimal regularization parameter in EXAFS analysis based on the L-curve-criterion without any external parameter. The L-curve is a log-log plot of the norm of regularized solution versus the norm of the corresponding residual norm. The optimal regularization parameter is chosen as a maximum of the L-curve curvature. We apply this method in two experimental cases: crystalline Cu with well-known structure and aqua-ion Cm⁺³ with unknown structure. The optimal regularization parameter leads to a stable solution with a good convergence of the iterative process.

The anharmonic vibration of ions in solids has been measured frequently by the EXAFS technique in recent years. However, the analysis of the anharmonicity in EXAFS is still complicated. In this article, we show a new method of simultaneous fitting with constraints (SFC) which is simple and useful for the analysis of anharmonicity. As an example, copper EXAFS spectra measured at 300 K, 500 K and 700 K were analyzed by this method. Also, we propose a useful EXAFS expression for anharmonic systems. We found the physical meaning of the parameters s and δ used in the EXAFS expression for anharmonic systems.

A good approximation for the electron self-energy or the electron quasiparticle properties is needed for an accurate calculation of x-ray absorption spectra. The GW approximation (GWA) has been found to be relatively reliable in predicting the quasiparticle energies and lifetimes in a large variety of systems. For solids, a part of a GWA calculation is the calculation of the inverse of the dielectric matrix ε⁻¹. We introduce an iterative method for calculating an accurate multipole approximation for ε⁻¹ and we apply it in GW calculations. Results for quasiparticle properties are presented for LiF and Si. For LiF we use these results to calculate the inelastic x-ray scattering spectra for energy loss close to the F K-edge. Other uses for this representation of ε⁻¹ will also be discussed.

The Fresnel theory with its numerous extensions is a well established method for the calculation of grazing incidence x-ray reflectivities for single surfaces and (multi-)layered systems. However, lateral surface correlations—which are always present e.g. for polycrystalline thin films—cannot be included in these calculations. Furthermore the application of the Fresnel theory is restricted to investigations of specular reflectivities, i.e. off specular reflectivities cannot be calculated. These limitations can be overcome by the application of the distortedwave Born approximation (DWBA). Simulations of grazing incidence reflection mode EXAFS spectra will be presented and the results obtained using different calculation procedures such as the Fresnel theory, the Névot–Croce model and the DWBA are compared. Furthermore, we will also prove the existence of a fine structure similar to EXAFS which can be observed in the region of diffusely scattered intensities. We will show that this new EXAFS technique is surface sensitive even for grazing angles above the critical angle of total reflection.

Multiple-scattering extended x-ray absorption fine structure (MS-EXAFS) was used to investigate the local structures around Ga atoms from the first to third coordination shells for GaAs crystals. The results revealed that among all the 7 multiple scattering paths in the first three coordination shells of Ga atoms, the dominant one is the scattering pathway of Ga₀ → As₁ → Ga₂ → Ga₀ (DS2). The DS2 path is almost out of phase with the single scattering path (SS2) of the second shell, and destructively interferes with the SS2 path. The amplitude ratio of DS2 to SS2 is about 25%. We provide a simple and feasible MS-EXAFS analysis method for investigating the local structure of the first three shells of III-V semiconductors with the zinc-blende structure.

In the Ge-structure, the forbidden Bragg reflections hk0 (h + k = 4n + 2) can be excited at the Ge K-edge due to both dipole-quadrupole scattering and dipole-dipole scattering of thermally vibrating atoms. The dipole-dipole contribution is referred to as TMI (Thermal Motion Induced) and is caused by the dependence of the atomic tensor form factors on the relative atomic displacements. This effect explains the strong increase of the 600 forbidden reflection intensity with temperature observed in experiments. In the present paper, both the dipole-quadrupole and the TMI contributions to the structure factor of the 600 reflection are calculated using the FDMNES code. Two models are considered, one assuming only displacements of the scattering atom, the other assuming all atoms in a supercell randomly displaced. Both approaches reveal a strong dependence of the dipole-dipole contribution to the tensor atomic factor on the atomic displacements and thus give a qualitative explanation of the temperature behavior of the forbidden reflection 600 observed in Ge.

Due to the lack of long-range periodic order in quasicrystals there are restrictions concerning a straightforward structure analysis on base of x-ray diffraction data. Computed reflection intensities in x-ray diffraction patterns, which are strongly affected by the shape and occupation of hypothetical atomic surfaces, need to be compared with experimental data. The interatomic short-range correlations as to be determined by means of DAFS and XAFS have to be in agreement with these structural models. The use of linearly polarised x-rays allows for orientation sensitive determination of otherwise averaged short-range order information. Additionally wave vector-selectivity of DAFS can yield short-range order information sensitive to sites occupied by atomic species within the coherently scattering structural units.

Structural models of decagonal Al-Co-Ni were applied to compute theoretical DAFS and XAFS functions. Calculation of both, energy-dependent structure factors and pair distribution functions obtained within a hypothetical cluster of app. 81 000 atoms as the basis of computation of DAFS are outlined.

Co-K and Ni-K DAFS and XAFS measurements at 3 independent reflections of a decagonal Al₇₀Co_9.5Ni_20.5 single crystal were performed and the experimental data were subjected to quantitative evaluation. The reflections used involved wave vectors parallel and perpendicular to the periodic direction and in a third inclined direction. In agreement with our simulations DAFS of individual reflections and thereby corresponding shortrange orders exhibited no differences within the error limits. The same was found for the case of polarized Co-K and Ni-K XAFS results.

Interplanetary Dust Particles (IDPs) are derived from primitive Solar System bodies like asteroids and comets. Studies of IDPs provide a window onto the origins of the solar system and presolar interstellar environments. We are using Total Reflection X-ray Fluorescence (TXRF) techniques developed for the measurement of the cleanliness of silicon wafer surfaces to analyze these particles with high detection sensitivity. In addition to elemental analysis of the particles, we have collected X-ray Absorption Near-Edge spectra in a grazing incidence geometry at the Fe and Ni absorption edges for particles placed on a silicon wafer substrate. We find that the iron is dominated by Fe₂O₃.

Correlations in the atomic motions can significantly change the interpretation of thermal effects in structural data. Including correlations of the stretching of the Zr-O bond with transverse O vibrations in the W-O-Zr linkage, in ZrW₂O₈, can explain the apparent discrepancy between a small σ_W–Zr² in EXAFS data and a large O thermal parameter U². This work also shows that in some cases a small value of σ² does not always mean that the vibration frequency is high.

The rutile-type structure is found in many dioxides. The rutile samples in this study, difluorides of the first-row transition-metals, MF₂ (M = Mn, Fe, Co, Ni), are important materials from the view point of electronic and magnetic properties. Although almost rutile-type difluorides have the positive thermal expansion coefficient, FeF₂ has a negative thermal expansion coefficient along the c axis in the high temperature region. In this study, we could obtain a detailed information about the thermal vibration of atoms by the analysis of EXAFS Debye–Waller factors. We discuss on the atomic momentum in the local structure of the difluorides. The EXAFS Debye–Waller factor is sensitive to short-range correlation of mutual atomic motions.

The displacement correlation functions (DCF) for each neighbor atom were determined by using both the mean square relative displacement (MSRD) and the mean square displacement (MSD) by x-ray diffraction. It was proved that DCF/MSD in the second-nearest neighbor atoms of FeF₂ is small, compared with other difluorides. This result suggests that in FeF₂, the correlation between second-nearest neighbor atoms (Fe-Fe) is weak. Furthermore, we could estimate the force constant between absorbing and scattering atoms from the temperature dependence of EXAFS Debye–Waller factor. The value of the force constant suggests that in FeF₆ octahedron in FeF₂, two apical bonds are stronger than four equatorial bonds.

Copper and silver oxide share the rather unusual cuprite structure, formed by two interpenetrating networks of corner-sharing M₄O tetrahedra (M = Cu, Ag). Negative thermal expansion of the cell parameter has been observed from 5 to about 200 K for Cu₂O and up to 470 K for Ag₂O by powder diffraction. In the case of Ag₂O, it has been shown by EXAFS that the lattice contraction is accompanied by an expansion of the Ag-O distance and that the deformation of the Ag₄O tetrahedral is not negligible. In this work we present a comparison between EXAFS and XRD results for both compounds. The comparison between local and lattice thermal expansions, measured by EXAFS and XRD, respectively, and the differences found between the two compounds, allow to gain original insight on the mechanism of negative thermal expansion in framework structures.

Xray absorption finestructure spectroscopy was used to ascertain the individual metal oxidation states involved during the electrochemical insertion and extraction of lithium with layered Li_xNi_0.5Mn_0.5O₂ electrodes in lithium cells. These results, along with electrochemical cycling data, suggest that the Li_xNi_0.5Mn_0.5O₂ (0 < x ≤ 2) electrodes operate predominantly via two-electron redox couples, Ni⁴⁺/Ni²⁺ and Mn⁴⁺/Mn²⁺, between 4.5 and 2.0 V (0 < x ≤ 1) and below 1.07 V (1 < x ≤ 2) versus metallic Li, respectively. In the upper voltage region, the Ni-O bond changes by nearly 0.14 Å, while the Mn-O bond remains at nearly a fixed length. In the low-voltage region, the LiNi_0.5Mn_0.5O₂ electrode undergoes a two-phase reaction with Li to form a dilithium compound, Li₂Ni_0.5Mn_0.5O₂; during this reaction, charge transfer occurs at the Mn metal center.

The homogeneity of typical electrolessly plated Pd/Ag membranes for H₂ separation was investigated with XAFS and XPS depth profiling. Next the crucial mixing of the separate Pd and Ag layers, obtained after the two sequential plating steps, was followed in situ with XRD. The results show that some low temperature alloying procedures found in the field are insufficient for obtaining a well-mixed Pd/Ag alloy membrane.

The Pd/Ag-H XANES was determined for the first time. In contrast to the Pd-H and Pd/Ag systems, shifts in electron density from the Ag or H atoms to the Pd could not satisfactorily explain the observed XANES. Not only is the intensity of the whiteline higher than expected, the shape and the intensity of the anti-bonding Pd 4d H 1s feature have also significantly changed. Local geometry is expected to account for these deviations.

When complex metal oxides show locally ordered substitution of cations amongst crystallographic sites, a single-model description of the structure is relatively straightforward. Distinct local and long-range space groups, element specific cation sites, and local distortions of the oxygen lattice may be employed to give a reasonable description of the structure. Averaging over possible orientations of the local cell may be performed to simulate the effect of domain structure or stacking faults where a dual space group description is inappropriate. Full multiple scattering calculations, over multiple edges, may be performed using these models, allowing all the XAFS data to be analysed within a cluster of 5 Å or more, and information on cation-cation correlations may thus be obtained. When substitution is more or less random, such approaches are less helpful. In order to extend the range of compounds which can be studied using the combined XAFS/Powder Diffraction (PD) method, a Reverse Monte-Carlo method has been developed, which includes multiple scattering XAFS contributions, and allows crystallographic symmetry to be superimposed on the finite model. Various restraints can be applied, for example, to minimise the difference between the structure and the starting model, to maximise the symmetry of a particular site, or to minimize unreasonable departure from bond valence sums. The necessity for such a method and an example of its application is given by reference to the disordered 8–8–20 perovskite derivative La₈Ni₄Co₄O₂₀.

It is well known that metallic contamination on the silicon wafer, suffered during VLSI fabrication processes such as thin film depositions and etching, brings about lowering device performance. Determination of the chemical or structural properties of contamination metals is necessary in order to specify and remove the cause of contamination. However, the measurements are extremely difficult, because the contamination metals have very low concentrations. Grazing incidence XAFS by the x-ray fluorescence yield method is useful for the purpose. We applied the technique for the investigation of iron and copper contaminations on silicon wafers after fabrication processes.

The silicon wafers contaminated intentionally in the process chamber were used as samples. The contamination level of iron and copper was of the order of 10¹¹–10¹³ atoms/cm². The measurements were performed at the beamline 12C of the Photon Factory in KEK. The incident angles from the silicon surfaces were about 1 degree. A Lytle type ionization chamber was used in order to detect x-ray fluorescence photons in large solid angles. Good quality spectra were obtained. It was found from the analysis of the spectra that iron is mainly binding to fluorine and copper is binding to chlorine. The results were very useful for process improvements.

XAS provides clear evidences that the tetravalent cations are not incorporated within Layered Double Hydroxide (LDH) sheets. The cations are segregated, presenting a local order close to that of SnO₂ rutile. However, the nature of the LDH influences slightly the local order probably due to some surface effect microtexture. Variation of the cell parameters for the LDH materials are explained by a substitution of Al cations by divalent cations M(II).

Mn(II) doped SnO₂ thin films used for shielding fluoride glasses against corrosion were investigated by x-ray absorption spectroscopy (EXAFS and XANE)S at the Sn and Mn K-edges. The effect of firing treatment on the densification of the films was studied. It has been evidenced a partial change of Mn valence from 2.3 to 2.6 upon heating which is attributed to a change of ratios of two Mn sites: grafted divalent Mn ions at the surface of SnO₂ nanocrystallites and trivalent Mn ions embedded into a substitutional solid solution with Sn.

Transmission XAFS measurements were performed on lanthanum chloride (LaCl₃) and LaCl₃-Li₂O mixture at various temperatures using La-K x-ray absorption edge. A distinct phase shift in the EXAFS oscillations was observed in going from the solid phase to the molten phase in LaCl₃. The results of curve fitting to the predominant peak in the structure function of LaCl₃ in real space, corresponding to the La³⁺-Cl⁻ 1st coordination shell, reveal that both the inter-ionic distance and coordination number of chloride ions around a lanthanum ion decreased with increase in temperature to above its melting point. The short-range structure of LaCl₃-Li₂O (xLi₂O = 5 mol%) mixture appears to be almost similar to that observed in pure LaCl₃.

Transmission XAFS measurements were performed on PbF₂ and LiF-PbF₂ at various temperatures using Pb-L_III x-ray absorption edge. Distinct phase shift of EXAFS oscillations was observed at the temperature range of superionic conductance phase transition in PbF₂. From the results of curve fitting to the predominant peak of PbF₂ in real space which is considered to be Pb²⁺-F⁻ correlation, we can reveal that both inter-ionic distance and coordination number decreases with increasing temperature from β phase to liquid phase through the superionic conductance phase. Structural change in LiF-PbF₂ shows the same tendency with that of pure PbF₂.

The structural parameters and the electronic structure of the complex between cerium(III) and N,N'-dimethyl-N,N'-diphenylpyridine-2,6-carboxyamide (DMDPhPDA) were studied by XAFS, and both luminescence and excitation spectroscopes. We investigated the fundamental aspects of this material as the ligand is promising for the separation of trivalent actinides and lanthanides. The Ce-K XAFS spectra were measured at the SPring-8 synchrotron facility in Japan. It was determined that the bond distances between the carbonyl oxygen and cerium, and between the pyridyl nitrogen and cerium were about 2.49 and 2.67 Å, respectively. The angle between the Ce-N bond and the p_z axis of the lone pair of the pyridyl nitrogen is 180° for the solution state, suggesting covalent interaction between cerium and the nitrogen of the DMDPhPDA ligand. Emission from this system is severely quenched, and red-shifts, and supports the presence of a strong inner sphere complexation between cerium and the nitrogen atom of the pyridyl group. From the XANES spectrum, the oxidation state of cerium was determined to be trivalent.

The structural parameters of technetium(VII)-uranium(VI)-tri-butyl phosphate (TBP) were determined by EXAFS to elucidate the mechanism of co-extraction of technetium in the presence of uranium(VI). Sample solutions were prepared by solvent extraction methods. The bond distance between uranium and oxygen of TcO₄^- is 2.97 Å: that of U-Tc is also observed at about 3.5 Å, suggesting that a TcO₄^- molecule exchanges with nitrate ion in the UO₂(NO₃)₂(TBP)₂ complex. However, the interaction of zirconium-rhenium of Zr(NO₃)_x(ReO₄)_4-x(TBP)₂ complex could not be observed. Although the rhenium also co-extracted, like technetium, by TBP in the presence of U(VI) and Zr(IV), this result indicates that ReO₄^- interacts with Zr through water.

Silicon carbide polytipes 6H-SiC and 3C-SiC were characterized by optical absorption at the C K edge in the near edge absorption region.

3C-SiC and 6H-SiC showed similarities for energies about 15 eV above the edge.

Marked differences were found in the near edge region. A picture based on the p distribution of empty states was suitable to describe the main features of 3C-SiC. 6H-SiC showed important absorption anisotropies traceable to the anisotropies of the scattering paths as shown by full multiple scattering calculation performed by MXAN code. The role of self consistency is also discussed.

Anti-bixbyite-type zinc oxynitride powders Zn₃(N_1-xO_x)_2-y could be prepared by directly nitriding zinc powder under ammonia gas flow. Zn₃(N_0.91O_0.09)_1.98 could be obtained after 168 hours of nitridation at 500 °C. X-ray absorption spectra near N and O K-edges for some zinc oxynitrides were recorded in both total electron yield and fluorescence modes. The two spectra provide complementary information on the near surface, and on what can be considered as the bulk of the powdered zinc oxynitride. O K-edge spectra clearly appeared for all the measured oxynitrides in both the total electron yield and fluorescence modes. However, only the N K-edge fluorescence yield spectrum was detected even for the nitrogen-richest oxynitride Zn₃(N_0.91O_0.09)_1.98. These results imply that the prepared zinc oxynitrides were covered with some ten nanometers of oxide layers and that nitridation of zinc powders would proceed by thinning down the oxide layers.

Six-coordinated silicon ^[6]Si was observed by Si and P K-edge XAFS measurements in xLi₂O-ySiO₂-(100-y)P₂O₅ glasses (x = 25 and 33, y = 40, 45, 50, 55, and 60). Si K-edge EXAFS spectra of the glasses indicated the co-existence of ^[6]Si and four-coordinated silicon ^[4]Si. The proportion of octahedral [SiO₆^6-] to ^[6]Si depends upon the alkali content and the [SiO₆^6-]/[SiO₄^4-] tetrahedral ratios were estimated by Si K-edge XANES spectra. The interatomic distances were 1.88–1.90 Å for Si-O and 1.55–1.61 Å for P-O and the amounts of [SiO₆^6-] were 11.8–46.9%.

X-ray absorption near edge structure (XANES) spectra, at the Na and Al K-edge, have been measured for Ca-Na aluminosilicate glasses. This allows a determination of the local cationic sites corresponding to 6–8 oxygen neighbours in a distorted first shell for Na and to 4 oxygen neighbours for Al. The Al XANES spectra show a strong dependence on the medium range organisation of the polymeric network.

BIMEVOX ceramics with different molar fraction of ME = Mg, Si, Zr, Zn have been investigated. X-ray absorption spectra have been measured for K edges of vanadium and zinc. The XANES at the vanadium K edge undergoes a conspicuous change for the metal dopant concentrations exceeding dopant solubility limits. Position of the pre-edge peak indicates the valence state of vanadium to be 5+ in all studied BIMEVOX'es. Vanadium coordination, as inferred from the EXAFS data, shows similarity for all dopants used, with two characteristic distances to oxygen atoms. An estimate of oxygen occupation numbers is given. Local environment of zinc atoms has an average coordination number ca. 4, and exhibits shorter interatomic distances to oxygen atoms than vanadium.

By evaporation on a clean native or thermal silica film, sodium atoms incorporate into the silica network and Na becomes surrounded by a well defined local structure. Exposure to oxygen transforms this (Na + SiO₂) glassy system to a crystallized compound close to Na₂SiO₃. Higher Na coverage of the clean silica surface leads to a metallic sodium multilayer, which transforms after the same oxygen dosing to pure Na₂O.

The distributions of unoccupied electronic states in the conduction bands of MgS and CaS have been determined. It has been found that the bottom of the conduction band of MgS is formed by Mg s and S s states, and of CaS by S d, s and p states. The partial electronic densities of S p and Fe d states in the conduction band of FeS (B8 phase) have been calculated. Interaction between these states in the bottom part of the conduction band of iron sulfide has been studied. A special kind of hybridization has been found it has been shown that the sulfur p states are "squeezed out" of the energy region of the iron d states.

Further understanding of the electrochromic mechanism taking place in anodically colored nickel oxide was achieved by XAS. From EXAFS simulation we were able to determine the percentages of electrochemically active phases and confirm the dissolution of the oxidized one, which was previously assumed by electrochemical characterization.

SnO₂ and doped Sb:SnO₂ sol, prepared by a precipitation-peptization sol-gel process, has been used as a host for the incorporation of an organic semiconductor, the perylene dye (PTCDA). The structure of the SnO₂ gel host together with the effect of inorganic (Sb) and organic (PTCDA) doping is studied with EXAFS at the Sn and Sb K-edge. Distinct neighbor shells are resolved only up to 4 Å. The corresponding radii are the same as in a cassiterite crystal structure with a 60% reduction in the Sn neighbor population. In the spectra at the Sn edge, the doping with Sb and/or a small concentration of PTCDA produces no detectable effect. At higher content of PTCDA, however, the number of the first oxygen neighbors is diminished by ∼30% indicating that the disordered organic groups from the dye molecule reach right into the Sn neighborhood. In the weaker Sb EXAFS spectra only the first shell of oxygen neighbors is resolved: again the static disorder is higher in the presence of the organic dopant.

We have studied the chemistry of S species in tribofilms generated on steel blocks from belt-drive continuously variable transmission fluids using x-ray absorption near-edge structure (XANES) spectroscopy. First, we examined S K-edge XANES spectra of tribofilms generated using a friction tester from four kinds of fluid which have different friction properties. It is suggested that sulphides such as FeS, alkyl sulphide and ZnS in the tribofilms might increase the friction coefficients of the tribofilms. Second, we examined the XANES spectra of tribofilms collected in both fluorescent yield (FY) and conversion electron yield (CEY) modes. FY and CEY spectra of a fluid were compared and it is found that ZnS content in the surface region might be higher than that in the bulk. On the other hand, the chemistry of the S species in the other three tribofilms might be almost uniform as far as the near surface and the bulk are concerned.

Spectroscopic studies of transition metal (Tm) and rare earth (Re) oxides, combined with ab initio theory identify the band edge electronic structure of alternative high-K dielectrics. The lowest conduction band states are derived from antibonding transition metal d*-states with a π symmetry and show strong final state effects. Applied to the complex Tm/Re mixed oxides of the general form ReTmO₃, this approach identifies a novel way for obtaining separate and independent control of band gap energies and dielectric constants through local bonding arrangements in which Tm and Re atoms are nearest neighbors to the same oxygen atom.

In situ EXAFS spectra of liquid, vitreous and crystalline zinc chloride under pressure and temperature, have been obtained and analysed using advanced techniques for data analysis (GNXAS). A detailed experimental investigation of the shortrange structural properties of zinc chloride is presented. X-ray absorption measurements of solid and liquid ZnCl₂ have been collected in the P = 0–12 GPa and T = 296–800 K ranges of pressure and temperature, using synchrotron radiation. The analysis of the signal in vitreous and liquid ZnCl₂ has been performed using a technique that allows to extract information on the radial distribution function g(r) obtained from molecular dynamics simulations or previous diffraction determination.

The solubility of actinides and actinide surrogates in a nuclear borosilicate glass was studied with cerium, hafnium, neodymium, thorium and plutonium. Cerium is a possible surrogate for tetravalent and trivalent actinides such as plutonium, hafnium for tetravalent actinide such as thorium, and neodymium for trivalent actinides such as curium or americium. X-ray absorption spectroscopy was used to obtain data on the local environment of the dissolved elements in the glass network. For glasses melted at 1200 °C, the solubility limits of the elements studied were as follows Nd > Ce > Th > Pu > Hf. A correlation has been established between the cation bonding covalence, the oxygen polyhedron and the solubility limit of the elements: the greater the solubility, the larger the oxygen bonds.

In order to understand precisely the changes induced by the reversible reaction of lithium with the electrode materials, XAS has been proved in many cases to be very efficient. The transformations generally concern the structure of the compound, at a short or a long range, and the oxidation state of the active element. We have studied, at the vanadium K edge, the behaviour of the compound Li_1.2V₃O₈, a promising electrode material for the lithium batteries. The XAS experiments have been performed, ex-situ or in-situ, in a classical way on systems close to equilibrium and, for the first time, during the battery cycling in using a dispersive XAS set-up. A plastic battery has been designed for this purpose and connected to an automated battery cycling system. The XANES part of the spectra has been decomposed into few simple mathematical functions and the results obtained at equilibrium and out of equilibrium are compared. The significant differences have been analysed in considering the voltage variations.

The mesoporous titania prepared by templating with hexadecylamine has an amorphous nature with a narrow pore size distribution centered at 2.8 nm and a Brunauer–Emmett–Teller (BET) surface area of 1230 m² g⁻¹. The extremely large surface area implies that most of the atoms are exposed at the surface. XAFS spectroscopy was applied to investigate the microstructure of mesoporous titania. The EXAFS function, k³χ(k), was considerably different from that of anatase. The amplitude decreased significantly in the large k region, suggesting large static and thermal disorders of the Ti-Ti bond. The third peak in the radial distribution function, which appeared at 3.4 Å in anatase and was attributed to the Ti atoms at the next nearest neighbouring site, was hardly observed in the Fourier transform of mesoporous titania. A comparison of the spectra at different temperatures revealed that the temperature dependence of the Debye–Waller factor for the Ti-Ti bond was significant. σ² was plotted against temperature and the effective surface Debye temperature of mesoporous titania was calculated to be 365 K. This is significantly lower than for the bulk titania crystals, 520 and 530 K for anatase and rutile, respectively.

Determination of structures using x-ray powder diffraction is complicated if the reflection intensities are mainly influenced by the scattering from heavy atoms and the atomic coordinates of light atoms remain uncertain. A method like EXAFS, which is sensitive to short range order, gives reliable atomic distances in the surroundings of heavy atoms with a precision of ±0.02 Å. The probability for obtaining the complete structure from x-ray powder diffraction increases if one includes parameters derived from EXAFS measurements as restraints during the procedure of structure solving. We demonstrate the potential of combining EXAFS and x-ray powder diffraction by solving the structure UO₂[H₂AsO₄]₂·H₂O. The procedure starts with the determination of space group and cell parameters from XRD powder data. In a second step the absolute values of the structure factor |F| are separated by iterating a decomposition formula. The heavy atom positions are determined by direct methods. In the third step atomic distances of coordination polyhedra are estimated using EXAFS. Subsequently, the complete coordination geometries around the heavy atoms including reliable distances are used as restraints in the structure solving and refinement procedure.

Dilute nitrides, in particular In_xGa_1-xAs_1-yN_y are very interesting alloys because of their actual and potential applications in the field of telecommunications and photovoltaics. A full knowledge of the local structure around each kind of atom, in particular the local ordering, is of fundamental importance because it is predicted to affect the electronics properties of these alloys. In this work we investigated the local environment of N and In by X-Ray absorption Fine Structure (XAFS). By exploiting the polarization dependency of XAFS we were able to demonstrate that N is fully substitutional to As. The lineshapes of the N K-edge XANES spectra are in fact identical, setting different grazing angles, which is a fingerprint of the cubic geometry of the N site. This information has been exploited to generate atomic clusters that very well simulate the experimental N K-edge XANES in the Full Multiple Scattering approach and to elaborate a multi-shell fit for XAFS data at the In K-edge. We concluded that N preferentially links In atoms, even if this short range ordering is by far weaker than the predicted one.

The Ti K-edge EXAFS for PbTiO₃ measured in the temperature range including the critical temperature (763 K) due to the phase transition from tetragonal to cubic phase is discussed from the local point of view. Three kinds of atomic pairs, shorter Ti-O(1), medium Ti-O(2) and longer Ti-O(3) were analyzed independently. The interatomic distance of Ti-O(3) changes at T_c discontinuously and shows a "displacive" type transition. On the other hand, EXAFS shows that the lattice distortion remains even in cubic phase, which indicates "order-disorder" type transition. The peak intensity at the pre-edge region in XANES, which indicates the distortion of Ti atoms along the c-axis of the oxygen octahedron, corresponds to the distortion obtained from EXAFS analysis.

A series of mononuclear complexes with 1-phenyl-3-(2-phenylsulfanyl-phenylamino)-pent-2-en-1-one (Ia) and 1-phenyl-3-(2-phenylsulfanyl-phenylamino)-but-2-en-1-one (Ib) ligands, which mimics the active site of copper, cobalt and nickel proteins, have been synthesized and structurally characterized by EXAFS.

EXAFS analysis has shown that NiL₂ and CoL₂ complexes with L = Ia are hexacoordinated by added Ni-S and Co-S bonds in contrast with square-planar NiL₂ (CoL₂) complexes with L = Ib. The CuL₂ complexes with both L = Ia and L = Ib ligands have the CuN₂O₂ planar coordination.

The local environment and the charge state of Tm atoms in PbTe were studied by EXAFS and XANES techniques at the L_III absorption edge of Tm (8.648 keV). It was revealed that Tm atoms predominantly substitute for Pb atoms in PbTe and are surrounded by Te atoms at a distance of 2.99 ± 0.02 Å. Tm atoms were found to be in Tm³⁺ charge state independently of the section of the phase diagram used for Tm doping. These results are in agreement with the results of previous investigation of the Pb-Tm-Te phase diagram. Electrical studies of Pb-Te-Tm with large deviation from stoichiometry revealed that the electron concentration was about one order of magnitude lower than the total Tm concentration and remained nearly constant (about 10¹⁹ cm⁻³) while varying the sample composition. Reduced electrical activity of the Tm impurity in PbTe was explained by effect of selfcompensation.

We have investigated the lattice relaxation around impurity atoms at the anion sub-lattice in CdTe, such as As acting as acceptor and Se which is isovalent to Te, with flourescence detected EXAFS. We experimentally verify the lattice relaxation with a bond length being reduced by 8% around the As atom as inferred indirectly from ab-initio calculations of the electric field gradient in comparison with the measured value in a PAC experiment (Lany S et al, 2000 Phys. Rev. B62 R2259). In the case of the isovalent impurity atom Se, the bond length is similarly reduced as determined experimentally by EXAFS and by model calculations with the density functional theory implemented in the WIEN97 program. In contrast to this inward relaxation, preliminary calculations for Br in CdTe, the next element in the series As, Se, and Br, which acts as donor at the Te sublattice, indicate an increase in bond length, an interesting prediction waiting for experimental verification.

The temperature dependence of EXAFS Debye–Waller factors in La_0.63Ti_0.92Nb_0.08O₃ perovskite with cation deficiency was investigated with the cumulant expansion method. The measurements of the Ti and Nb K-edge and La L3-edge EXAFS spectra were carried out in the transmission mode at temperatures up to 800 K. The obtained local bond distances of 1.95(1) Å for Ti-O, 1.98(1) Å for Nb-O and 2.65(1) Å for La-O are significantly smaller than the expected values on Shannon's radii. This characteristic is attributable to the presence of the cation deficiency. The effective pair potentials, V(u) = αu²/2 + βu³/3, were evaluated and the potential coefficients α and β for the Ti-O bond in La_0.63Ti_0.92Nb_0.08O₃ are 6.6(1) eV/Ų and −42(3) eV/ų, respectively. The Ti-O bond in the A-site-deficient La_0.63Ti_0.92Nb_0.08O₃ has relatively larger anharmonic and soft potential coefficient than that in ordinary CaTiO₃ perovskites.

Temperature dependence of XAFS spectra of the Perovskitetype proton conductor SrZr_0.9Yb_0.1O_3-δ at Sr and Zr K-edges and Yb L3, L2 and L1-edges have been investigated. Chemical shifts to lower energy and change in XANES spectra are observed with increasing temperature. No change in the XANES spectra and in the threshold energies of the Yb L3-, L2- and L1-edge was observed. This indicates that the effective charges (oxidation states) of the Sr and Zr ions change with oxygen loss while the effective charge of the Yb ions were maintained. The unit cell volumes increase with increasing temperature with a slight bend between 700 and 950 K. This bend of the unit cell volumes vs. temperature is considered to be due to the loss of oxygen, which is consistent with the result of a weight loss in TGA observed in the same temperature range. The mean-square relative displacements (MSRD) of the backscattering atoms with respect to the absorbing atom were also determined by EXAFS. Its temperature dependence increases with a slight bend between 700 and 950 K, which is considered to be due to a local structure change accompanied by the loss of oxygen rather than that by the phase transition at 948 K. It is proposed that the changes of local structure and effective charges of Sr and Zr ions must play an important role in the protonic conductivity.

Xray absorption spectroscopy was used to probe the shortrange structure in lanthanumdoped lead titanate ceramics (Pb_1-xLa_xTiO₃) for x ranging from 0.0 to 0.30. A comparison of the XANES spectra and the x-ray diffraction (XRD) results indicates that the local structure around Ti atoms had a different compositional dependence. According to the XANES data, even for the sample containing 30% of lanthanum, for which the XRD analysis indicated the existence of a cubic structure, a local distortion around Ti atoms persisted. The intensity of the pre-edge feature of the PLT30 sample decreased by a factor of only two when compared with the lanthanum-free sample.

Amorphous germanium (a-Ge) structure is known to show a complex behavior upon pressurization. Here an XAS experiment on a-Ge at high pressure and temperature is presented, which is aimed to investigate such behavior and verify the presence of polyamorphism. High quality a-Ge EXAFS spectra (Ge K-edge) have been collected up to 8.3 GPa. The data analysis, realized using the GNXAS package, gives precise values of the first neighbor bond lengths at various pressures. Two well defined behaviors of the a-Ge local atomic structure have been observed, depending on the sample temperature. At 475 K a-Ge starts to crystallize above 8 GPa. On the other hand, at room temperature, the data seem to indicate the occurrence of a transition toward a different amorphous structure, well before the start of the process of crystallization.

Er doped Si represent an interesting class of materials for the realization of light emitting devices based on Si technology. The local structure around Er ions is known to strongly affect the luminescence properties of the Rare Earth. In this work the Er site in Er + O doped silicon samples prepared by Molecular Beam Epitaxy has been investigated by x-ray Absorption Spectroscopy at the Er L_III edge. Samples with different preparation parameters such as the O/Er ratio and thermal treatments were investigated. Data were fitted using a model consisting in a first shell of O atoms and a second shell of Si atoms and accounting for multiple scattering effects. The rare earth is found to be linked to 5–6 O atoms at around 2.23 Å whereas a well defined Er-O-Si bond angle of ≈136 deg is evidenced.

A number of Ag-bearing galena samples (PbS) has been investigated by Ag K-edge XAS in order to determine the Ag structural role within the host galena structure. Despite the very low absorber concentration and the high absorbance of the PbS matrix, XANES spectra were successfully collected for samples with Ag content down to 500 ppm. Theoretical spectra have been calculated with the CONTINUUM code in order to discriminate the contributions from Ag located in the two possible sites in the galena structure: the Pb site (located at Wyckoff position 4b, octahedral S coordination, site symmetry m3m), and an interstitial site (located at Wyckoff position 8c, tetrahedral S plus tetrahedral Pb coordination, site symmetry 43m). Experimental spectrum of diaphorite (a Ag-bearing mineral phase forming nano- to micro inclusions in Ag-rich galena) have been used for comparison.

The XANES experimental spectra show two different types of Ag environment:

• the samples with high Ag content display spectra similar to that of diaphorite, as evidenced by the theoretical spectra, suggesting that, when present in considerable amount, most of the Ag partitions into the diaphorite inclusions rather than entering the galena structure;

• trace level Ag-bearing samples display spectra very different from that of diaphorite. In view of the absence of micro- and nano-inclusions in the latter samples (confirmed by electron microscopy), these spectra are taken as representative of the Ag environment in the host galena structure. In these samples the comparison between experimental and theoretical spectra shows that the spectrum can be interpreted as the sum of the two contributions from Ag located in the 8c and 4b positions in the galena structure, in approximately the same proportions. Therefore, the data suggest that in this type of galena sample, half of the Ag occupies the vacant Pb site whereas the remaining part is located in the interstitial 4b site.

Lithium intercalation and deintercalation in crystalline TiO₂-electrodes (rutile and anatase modifications) was investigated ex situ using grazing incidence reflection mode x-ray absorption spectroscopy in a specialized cell which permits the removal of the electrolyte and the subsequent measurement of grazing incidence x-ray absorption spectra under a protecting noble gas atmosphere. Small changes observed in near edge x-ray absorption spectra indicated that the Ti⁴⁺ ions are reduced by the electrochemical lithiation, depending on the TiO₂ modification, Ti^3.5+ states as well as Ti³⁺ states are observed for rutile and anatase, respectively. Angle dependent experiments reveal that the intercalation is not complete for rutile, while anatase seems to be fully intercalated. In addition, a certain amount of Li remains in the anatase electrode after a complete intercalation – deintercalation cycle. The results suggest that Li-ions are generally accumulated at the electrode/electrolyte interface during both intercalation and deintercalation.

The structures of polyacetylene (PA) films with oriented chains have been intensively investigated with linearly polarized carbon K-edge near edge x-ray absorption fine structure (NEXAFS) for the first time. The angular dependence of linearly polarized peak feature has been observed from normal to glancing incidence, with respect to the stretched direction of the PA film. The polymeric chain orientation of the stretched trans-PA has been determined with the strong angular dependence of π*_C–C, σ*_C–H, and π*_C–C resonance. Heavily doped PA films with 6% FeCl₄⁻ or ClO₄⁻ show different near-edge peak features from the undoped PA films, especially in the energy region of ∼285 eV corresponding to electronic transition of C 1s electron to unoccupied π*_C–C molecular level. Upon doping, the resonance peak position for sp² hybridization of unsaturated C–C bonding is shifted to higher energy and the peak intensity is reduced significantly, which indicates that the cleavage of conjugated π bonds by p-doping occurs in the trans polymeric chain reducing the alternating double bond chain length. Although the peak features for σ*_C–H and σ*_C–C have been effectively changed, no angular dependence of the NEXAFS spectra are observed in the doped PAs.

The highly localized 4f electrons play an important role in forming of the electronic structure and properties of compounds. The 3d photoabsorption and resonant decay spectra of Cs halides represent an interesting case showing both the localized and spatially extended f wavefunction features. We present and discuss the Cs 3d x-ray absorption and resonant photoelectron emission spectra of the Cs halides. The Cs 3d absorption spectra exhibit a strong atomlike shape resonance behavior, solidstate effects play a minor role. The appearance of the spectral features, which are intrinsic to a localized state, in the decay spectra show that the Cs 3d photoelectron, temporally and spatially trapped in the Cs 3d shape resonance due to the potential barrier for εf electrons near threshold, has substantially localized nature.

The local structures of semiconductor InSb compound have been studied by in-situ XAFS in the temperature range of 300 and 823 K. Reverse Monte Carlo calculation is used to simultaneously fit both In and Sb K-edge EXAFS functions kχ(k) of InSb compound. The fitting results indicate that the average bond length R₁ (2.80 Å) and the average coordination number N₁ (4.0) of the first In-Sb (or Sb-In) shell of InSb (723 K) are similar to those (2.79 Å, 4.0) of crystalline InSb (300 K) with a zinc-blende structure, in spite of InSb compound possessing a large thermal disorder degree at 723 K. At the temperature of 828 K (T_m(InSb) = 798 K), the R₁ and N₁ of the first In-Sb shell are 2.90 Å and 5.8, and the R₁ and N₁ of the first Sb-In shell are 2.90 Å, and 5.5 for molten InSb, respectively. For molten InSb (828 K), the coordination numbers of the In-Sb (or Sb-In) first shell are mostly 5 and 6, and a few percent of In-In (or Sb-Sb) coordination appears in the first shell. It implies that the tetrahedron structures of the In-Sb (or Sb-In) covalent bonds of InSb compound have been destroyed in the liquid state.

We attempted to investigate whether the Ni valences change homogeneously in a grain of LiNi_0.8Co_0.2O₂ during charging/discharging Li-ion batteries. In situ XAFS measurements using x-ray microbeam with the size of about 1–2 μm were applied to measure position dependencies of Ni (Co) valences in a grain. In order to investigate the electronic changes caused by capacity fading, three types of coin cells for in situ XAFS measurements were prepared, the cell after one charge/discharge cycle, after 100 cycles at 60 °C and after aging at 60 °C for 21 days, respectively. Two-dimensional fluorescence maps of Ni and Co were obtained to determine measuring points in a grain (the center of a grain, the edge of a grain, etc.). Ni and Co K-edge XAFS spectra were collected in transmission mode for each point. As a result, no apparent differences depending on positions were observed for all types of the cells. It was concluded that the changes of Ni valences during charging/discharging batteries occur homogeneously in a grain, not depending on the degree of capacity fading.

The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of Nb₂O₅ and SnO₂ saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or ∼2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 °C and 2 kbar under relatively reducing conditions. Three "haplogranitic" compositions (a model granite in the system Na₂O-K₂O-AlO₃-SiO₂) were investigated: peralkaline (labeled "ASI 0.6"), metaluminous ("ASI 1.0") and peraluminous ("ASI 1.2"). One series of haplogranitic glasses ("SQ") were synthesized at intermediate oxygen fugacity conditions (∼10⁻⁹ atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated.

The tin-bearing glasses show Sn K-edge XAFS spectra that resemble that displayed by eakerite, a Ca-Sn silicate in which Sn(IV)O₆ octahedra share corners with SiO₄ tetrahedra (⟨Sn-O-Si⟩: 150°). However, the most reduced glasses show significant contributions arising from weakly bound Sn(II)O_n complexes. The niobium-bearing glasses show Nb K-edge XAFS spectra that most closely resemble that displayed by vuonnemite, a Na-Ti-Nb silicophosphate. Niobium forms NbO₆ clusters, also bonded to Si/Al second neighbors. The coordination geometry of niobium in the glasses is strongly influenced by both Nb content and alkalinity; H₂O content does not strongly influence the speciation of niobium. Fluorine-bearing Nb-glasses show unusual XANES spectra, which might be related to a decrease in the coordination number of niobium from 6 to 4 (or 5). However, based on Nb K-edge XANES calculations (FEFF 8), fluorine does not appear to complex niobium.

We have investigated solid electrolyte interfaces (SEI) of lithium ion batteries containing sulfur additive for electrolyte with S K-edge XANES spectra. Graphite anode and LiCoO₂ cathode were used as electrodes and ethylene sulfite (ES) was used as an additive for propylene carbonate electrolyte. Compared with XANES spectra of standard compounds, it is elucidated that the SEI layer on the graphite anode includes Li₂SO₃, ROSO₂Li, Li₂SO₄ and organic sulfur with C-S-C and/or C-S-S-C bonding. The XANES spectrum of the cathode shows that Li₂SO₄ and organic sulfur compounds with C-S-C and/or C-S-S-C are included in the SEI on the cathode. In the discharge state, the sulfur compounds in SEI layers on the anode dissolve into the electrolyte under high temperature around 120 °C although the dissolution of the sulfur species is not observed in the charge state. On the other hand, it is found that the rate of dissolution of the sulfur compounds in SEI layers on LiCoO₂ cathode is lower in the discharge state than in the charge state.

Structural changes of pyromellitimido-oxydianiline (PMDA-ODA) polyimide (PI) films by UV irradiation were studied by means of XAFS and XPS. UV irradiation in air was found to cause oxidative cleavage of the imide ring of the PMDA part, whereas that in vacuum changed the conjugated structure involving nitrogen but did not likely open the imide ring. The results indicate that the combined analysis of XAFS and XPS is a powerful tool for polymer surfaces.

A structural study of a niobium-peroxo-citrato complex in an aqueous solution, used as a precursor for the synthesis of ceramic oxides by an aqueous solution-gel route is performed by Nb K-edge EXAFS analysis. The results clearly indicate the formation of niobium-peroxo-citrato dimers via Nb-O-Nb links. Nb(V) ions are seven-coordinated including one Nb=O bond of a niobyl group and two Nb-O bonds from a side-on metal-peroxo group. The results are consistent with a previously proposed structural model based on Raman and UV spectroscopy studies.

Granular solids composed of Co dispersed in a Cu matrix attracted the attention of magnetism community due to several interesting characteristics. One of their most striking properties is the giant magnetoresistance. In this work we used EXAFS to study the Debye–Waller factor, or disorder, of a Co₁₀Cu₉₀ sample as a function of the temperature. Using the correlated Einstein model, we were able to separate the thermal from the static contribution to the disorder. We concluded that the granular alloy has static disorder comparable to that of bulk well crystallized Co. In other words, for the Co₁₀Cu₉₀ sample around Co atoms, most of the disorder has thermal origin at room temperature. This is explained basically as the influence of the Cu matrix on the atoms at the interface of the well defined Co particles.

The structures of mechanically alloying Fe₆₀Ni₄₀ milled for 5, 10, 20 and 40 hours were investigated by XAFS and XRD. The XRD patterns indicate that the α-Fe phase almost disappears and only the fcc phase remains after milling for 10 hours. The XAFS results further show that the RSF shape of Fe atoms is similar to that of Ni atoms for the MA Fe₆₀Ni₄₀ (10 h) alloy. The Debye–Waller factors σ₁ of the Fe and Ni atoms in the MA Fe₆₀Ni₄₀ (10 h) increase from 0.071 and 0.091 Å to 0.102 and 0.105 Å, respectively. These results demonstrate that the local structure of most Fe atoms in the MA Fe₆₀Ni₄₀ (10 h) has changed from bcc structure to fcc one after milling for 10 hours. With the milling time going to 40 hours, the σ₁ of both Fe and Ni atoms increase to about 0.117 Å, the R₁ = 2.48 Å and N₁ = 11.9 around Fe atoms are equal to R₁ = 2.48 Å and N₁ = 11.9 around Ni atoms and the magnitude peaks of the higher shells disappear for MA Fe₆₀Ni₄₀ (40 h). These results imply that the changes of local structure around Fe atoms are identical with that around Ni atoms in MA Fe₆₀Ni₄₀ alloys. We consider that the MA Fe₆₀Ni₄₀ (40 h) alloy is a homogenous solid solution.

We report a detailed analysis of O K-edges near edge x-ray absorption of maghemite, hematite and magnetite iron oxides. Measurements were performed on powder in Fluorescence Yield mode of detection.

Iron forms several stable oxides and its phase diagram is more complicated than that of other transition metal as Ni or Co. The differences in the local symmetry of the three iron oxides are related with the distinguishable NEXAFS spectra. In particular the spectra are characterized by a sharp doublet ascribable to transitions to the empty metal d-bands involving the t_2g and e_g states whose energy splitting and intensities depend on the structure and state of ionicity.

The NEXAFS spectra have been simulated and fitted by MXAN code. The aim of these simulations was the test of light Z element NEXAFS spectra calculation performed by phenomenological no-self-consistent potential in the near edge region, the most sensible to electronic properties details; a fit procedure of the potential parameters was performed in the extended NEXAFS photon energy range and subsequently used for near edge calculations. The MXAN simulations obtained in this way, reproduce the experimental data with good agreement and evidentiate the differences in the spectra of the three compounds. In particular maghemite, that has oxygen in two different sites, has been well simulated using potential details found for the other oxides hematite and magnetite.

We report on an EXAFS study of the local environment of manganese atoms in LaMnO₃ across the cell ordering transition temperature. During the EXAFS analysis the phase derivative method was used prior to conventional fits in order to prevent possible mistakes arising from the correlation between parameters in the fitting method. The combination of the two procedures assert the result that the local splitting in the MnO distance is maintained above the Jahn–Teller transition and support the order-disorder character predicted for this transition in LaMnO₃.

In this work, geometric structures for ferromagnetic nanoscale zinc-blende MnAs dots grown on a sulfur-passivated GaAs(001) were investigated by using fluorescence EXAFS measurement. EXAFS measurements revealed that MnAs dots grown on GaAs(001) substrate did not form NiAs-type structure but zinc-blende structure. The MnAs bond length in the MnAs dots is about 2.48 Å which is close to that which was estimated from lattice constant of zinc-blende MnAs obtained by density-functional calculations. Existence of zinc-blende MnS (β-MnS) phase was also observed by EXAFS measurements.

Structural evolutions in a heat-treatment process have been studied using Si and P K-edge XAFS in SiO₂-P₂O₅ sol-gel layers on silicon substrates. The Si K-edge EXAFS results indicate that structural changes occur between 1173 K and 1273 K. In the case of heat-treated samples at 1273 K, the Si-O interatomic distance is 1.63–1.64 Å. On the other hand, the distances are 1.66–1.68 below 1273 K. Furthermore, structural properties around Si and P in the sol-gel process have been studied. In the XAFS spectra, the ratio of P to Si shows 84% decrease after heat-treatment above 1073 K. For the Si-O and P-O distances, wet-gel has shorter interatomic distance than sol-gel raw solution, TEOS and TEP, respectively.

X-ray absorption technique was applied to analyze the local structures of fused and synthesized silica glasses before and after irradiation in a nuclear reactor. Si K-edge EXAFS revealed changes in the SiO₄ tetrahedron structure by the irradiation, i.e. a distorted tetrahedron in the silica glass returned to more regular one but the connection between neighboring tetrahedrons became looser. In addition, the detailed analysis of EXAFS spectra gave evidence for the formation of direct Si-Si bonding after prolonged irradiation, suggesting the appearance of Si precipitates in silica glass.

The pyramid-like Ge islands deposited on Si(001) substrate using molecular beam epitaxy at 300 °C reveal quantum dots (QDs) properties. Measurements of x-ray absorption fine structure at the germanium K edge (GeK XAFS measurements) have been performed using total electron yield and fluorescent detection mode. The influence of effective thickness of the germanium film, Ge nanocluster sizes and Si deposition temperature on the QDs microstructure parameters is revealed. Some information concerning the energy structure of the free states of the quantum dot was extract from x-ray absorption near edge structure (XANES) spectra for the first time.

Pr K-edge XAFS spectrum as a function of temperature in Pr_0.5Sr_0.5MnO₃ has been recorded on BL01B1 beam line at Spring-8, in order to study the effect of lattice distortions as the sample passes from a paramagnetic insulator phase at room temperature to ferromagnetic metal phase below 265 K and to an antiferromagnetic insulator phase at low temperatures. It is found that when the ferromagnetic to antiferromagnetic transition takes place, the MnO₆ octahedra rotate in the ab-plane and tilt away from the vertical along the c-axis. The tilting of the MnO₆ octahedra is responsible for the A-type antiferromagnetic phase.

Valence states and structural environments of polyvalent Fe and Ti ions in two different borosilicate glasses have been studied by X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The results indicate that different valence states of polyvalent metal ions usually exist simultaneously in glass matrix. Doping C favours the formation of reduced state of metal ion. Especially, Fe²⁺ ion can be reduced into neutral iron atom. Fe²⁺ ion generally occupies octahedrally coordinated site. Fe³⁺ ion tends to be in tetrahedral coordination with increasing total iron concentration. Adding oxidising agent can transfer the octahedral iron ions into tetrahedral Fe³⁺ ions. Ti⁴⁺ ions mainly occupy five-fold coordination sites in NBS1 and four-fold coordination sites in NBS2, depending on the existence of non-bridging oxygen ions in the glass matrix.

We examined the local environment of zirconium atoms in the Pb(Zr_0.53Ti_0.47)O₃ (PZT) sol, prepared from lead acetate and transition metal n-propoxides in 2-methoxyethanol, and in the as-pyrolyzed amorphous film deposited on (0001) sapphire. The immediate neighborhood of Zr atoms changes markedly upon transition from the sol to the amorphous film. Clustering of Zr species in the process of film formation in the form of Zr oxide nanoparticles is indicated.

Iron thin films of less than 100 nm have been grown on Si(100) wafers by DC magnetron sputtering at well-controlled substrate temperatures. Three different sets of samples have been prepared in order to study the influence of the preparation conditions on their magnetic properties: i) natural oxidized samples, ii) "in-situ" partially oxidized and iii) nonoxidized iron thin films. For the last two sets, a gold film prior to expose the air capped the samples. XRD and EXAFS experiments have been performed to obtain the size and the shape of the grains. They provide a columnar growth for samples prepared at room temperature and a diminution of the grain size along the normal to the surface when the preparation temperature decreases.

Ni and Si₃N₄ layers have been alternatively deposited by sputtering in order to study Ni clusters embedded in amorphous Si₃N₄. The nominal Ni layer thickness has been varied from 2 to 60 Å and the number of layers was planned to have a similar total amount of Ni. The decrease in the Ni-Ni coordination number observed by Extended X-ray Absorption Fine Structure spectroscopy has been used to study the microstructure of the Ni clustering. For small Ni layer thickness, the actual Ni layer becomes discontinuous and an average cluster diameter of Ni clusters can be determined. Ni metallic cluster in the Ni/Si₃N₄ system show a magnetization smaller than in bulk nickel, the decrease of magnetization of the cluster should be attributed to a dead skin at the surface of the Ni-clusters.

Sr₂FeMoO₆ double perovskits display low field MR at a relatively high temperature and unusual ferromagnetic properties. These compounds depicts metal to insulator transition increasing x above x_c ∼ 0.25. A comparative analysis of the near edge regions (XANES) suggests that iron is Fe³⁺ in the metallic range. Checking the end compounds, we found that the doped samples can be viewn as inhomogeneous distributions of the end compounds. This could help to distinguish between the two scenarios proposed to explain the metal to insulator transition. Moreover, the local atomic structure of Sr₂FeMo_xW_1−xO₆ as a function of composition (0 ⩽ x ⩽ 1) has been investigated by Extended x-ray absorption spectroscopy (EXAFS) a the Fe, Mo, Sr K-edges and W L_III-edge.

We have investigated the local structure of Ag nano-clusters deposited as thin films on silicon substrate by using a total conversion electron yield XAFS (x-ray absorption fine structure) method at Ag K-edge. High quality spectra were obtained from samples with thicknesses of 1–10 nm. We have found that these clusters have an fcc structure and that the interatomic distance does not depend on the thickness. The coordination number, N, however, changes with the thickness of the film. The N value for the first nearest shell as a function of the film thickness is compared with the theoretically expected value by taking account of the surface effect. For thinner films, the observed N values are smaller than the expected values. We have observed a correlation between the N value and the electromagnetic field intensity at the surface evaluated from IR measurement. The morphology of Ag nano-cluster particles must affect the local electric field intensity at the surface.

We have synthesized a new leadbased oxide Pb(Pb_1/3Ta_2/3)O₃ of the PbB'_nB''_mO₃ perovskite-type, where B'-sites are occupied by Pb²⁺ ions. The perovskite-type structure with cell parameter a = 4.14 Å was determined by powder x-ray diffraction. We have studied the XAFS of the Pb L_III-edge in Pb(Pb_1/3Ta_2/3)O₃. Our analysis confirms the presence of Pb²⁺ = B'site cations having a distorted octahedral oxygen coordination with a nearest-neighbour Pb-O bond length of R = 2.45 Å. The Pb-O distances for Pb²⁺ = A-site cations was found to be equal to R = 2.89 Å that is typical of perovskites. The presence of superstructural lines on the x-ray diffraction pattern as well as non-diffused permittivity maximum strongly support the presence of 1:2 long-range ordering in Pb(Pb_1/3Ta_2/3)O₃.

Hydrated thin films of nickel vanadium oxide (Ni_1−xV_xO_y), made by reactive DC magnetron sputtering, were studied by x-ray absorption spectroscopy at the Ni and V K-edges using synchrotron radiation. The XANES signals were analysed within the full-multiple-scattering formalism, whereas EXAFS data were modelled within the multi-shell multiple-scattering approach. We found that transparent films exhibit a nanocrystalline NiO-type structure with homogeneous distribution of V ions substituting Ni ions. Exposure of the films to ozone resulted in dark brown coloration associated with an appearance of Ni³⁺ ions and accompanied by a modification of the local electronic and atomic structures of the V and Ni ions. The largest changes occurred in the environment of the V ions, which presumably change their valence state from V⁴⁺ to V⁵⁺ and displace into off-centre positions by ∼0.4 Å.

Visible light sensitive zeolite photocatalysts have been prepared by metal ion-implantation of Ti-containing mesoporous molecular sieves with V ions (V/Ti-HMS) which can operate under visible light irradiation (λ > 450 nm). The metal ion-implantation with V ions was effective to shift the absorption band of Ti-containing molecular sieves to longer wavelengths. This V/Ti-HMS performed the photocatalytic reactions for the NO decomposition under visible light irradiation, while no reaction proceeded on the original Ti-HMS. XAFS analysis indicated that implanted V-oxide moieties existed having tetrahedral coordination and interacted with the tetrahedrally coordinated titanium oxide moieties. These XAFS results as well as the analysis with UV-VIS absorption measurements indicate that the charge transfer excited state of the tetrahedrally coordinated titanium oxide moieties interacting with the tetrahedrally coordinated vanadium oxide moieties plays a significant role in the photocatalytic reaction under visible light irradiation.

The electronic and geometrical structure of A₂FeMoO₆ (A = Ca, Sr, Ba, Ba_1/2Sr_1/2) compounds has been investigated by means of x-ray absorption spectroscopy at the iron and molybdenum K-edges. The Mo-O distances extracted from the Mo K-edge EXAFS spectra are almost identical for all compounds while XANES spectra show small differences depending on the divalent metal. The XAS spectra at the Fe K-edge showed significant differences instead. Our analysis suggests an influence of the divalent A-metal in the electronic state of iron and molybdenum. Both the chemical shift at the iron K-edge and the interatomic Fe-O distances, closely correspond to Fe³⁺ for Sr₂FeMoO₆ and Ca₂FeMoO₆ while a mixed valence state (between +2 and +3) is deduced for the Ba sample. Accordingly, the Mo valency is higher for the barium sample.

In the present contribution we show that x-ray absorption spectroscopy may be an effective way to obtain a detailed insight into nano-granular structures embedded in a glass matrix. For the first time we have employed the single energy x-ray absorption detection method to determine the diameter distribution of metallic granules embedded in a glass matrix. In particular, we have estimated the diameter distribution of Pb granules confined in a PbOSiO₂ matrix.

The composition dependence of shortrange structure was investigated for manganese borate glasses ((MnO)_X(B₂O₃)_1−X, X = 0.21, 0.30, 0.44, 0.52) by XAFS measurement. The manganese K-edge XAFS spectra of the glasses were measured at the beamline 4 (BL-4) station of the synchrotron radiation facility at Ritsumeikan University in Japan. From the XANES spectra, it was found that the manganese ion is divalent in the glasses and it does not vary with the MnO content. The EXAFS spectra indicate that the manganese ion is surrounded by four oxygen atoms with an interatomic distance of ca 2.1 Å. A notable composition dependence of the Mn-O correlation is not observed for the glasses.

0.2 mass% Mo in a high-strength steel has been investigated using x-ray absorption fine structure (XAFS) technique. Mo-K edge x-ray fluorescence XAFS spectra show the transition from Mo in solution in α-Fe matrix to Mo in carbides when the steel is annealed at 650°C. We have evaluated the atomic fraction of Mo atoms in solution and in carbides from curve fitting parameter of XANES spectra and from coordination number of iron surrounding Mo in the α-Fe matrix derived from an EXAFS analysis.

Resonant inelastic x-ray scattering is well suited to studying pre-edge features in x-ray absorption spectra. Here it is applied to the Ce L₃ edge in CeNi, CeNi₂, and CeNi₇. A relatively strong feature is observed corresponding to 4 f² final states. We show that its presence is not the consequence of 2p → 4f quadrupole transitions but rather to final state interactions with conduction electrons and Ni 3d states.

The coordination environment of titanium atoms in the x₁TiO₂-x₂BaO-x₃B₂O₃ system, where x₁ = 4%, 8%, 15% and x₂/x₃ = 8/9 (molar %), has been determined by X-ray Absorption Near-Edge Structure (XANES) spectroscopy at the Ti K-edge. The environment of Ti atoms in BBT powder amorphous samples prepared using a chemical method is composed by ^[4]Ti as the predominant specie but the ^[6]Ti specie is also detected. After crystallization, titanium environment in powder samples is predominately composed by ^[6]Ti species. The environment of titanium atoms in glassy samples produced by melting is very similar to that observed on the amorphous powdered samples. On the other hand, the environment of titanium in glass-ceramic samples is completely different from that of powder crystallized samples. A significant amount of ^[4]Ti specie was found after the crystallization in the glass-ceramic samples.

Greigite Fe₃S₄ is one of the two natural magnetic iron sulphides. Its formula and structure make it the sulphide equivalent of magnetite Fe₃O₄, leading to frequent confusions between these two spinelles in paleomagnetic studies and possible wrong interpretation of some paleaomagnetization measurements.

We have carried out high resolution EELS experiments and recorded x-ray magnetic circular dichroic spectra at the iron L_2,3 edges on natural and synthetic samples. The natural samples present a coreshell structure of crystallized greigite surrounded by an amorphous iron oxide phase. The differences observed on the XMCD signal of Fe₃S₄ compared to Fe₃O₄ could be explained by the presence of iron vacancies, Fe₃S₄ being a lacunary iron sulphide.

The process of iron film epitaxial growth on the 4×6 reconstructed surface of GaAs(001) proceeds through a transition between island (Volmer–Weber) and layer (quasi-Frank-van-der-Merwe) growth. We have examined the growth of iron on GaAs(001)-(4×6) in-situ by polarization-dependent XAFS in the total reflection mode. The onset of greater ordering in the film has been observed through the development of tetragonally-distorted iron. The distortion towards lattice-matching between the iron in-plane and the GaAs substrate is clearly evident immediately after the transition between growth modes. The resulting body-centered tetragonal structure persists to 30 monolayers, the largest thickness studied.

The magnetic behaviour of ferromagnetic/non-ferromagnetic/ferromagnetic trilayers is strongly dependent on the nature of the interface between layers, the strain in the layers and the extent of any interdiffusion or reaction between layers and substrate. In this paper, results are presented from a polarization-dependent in situ XAFS study of Fe/Pd/Fe trilayers epitaxially grown on GaAs(001)-(4×6). Fe and Pd K-edge spectra were obtained both above and below the critical angle for total reflection. The structure of iron grown on the Ga-terminated 4×6 reconstructed surface of the GaAs(001) substrate, for thicknesses greater than 6 monolayers, is tetragonally distorted from its natural bcc structure with contracted and expanded lattice constants in the in-plane and out-of-plane directions, respectively. The intermediate Pd layer shows distortion from its natural fcc structure. Alloying at the interface with the underlying Fe is restricted to a depth of 0.5–1.0 monolayers (ML). The upper layer of Fe shows tetragonal distortion similar to the layers of Fe grown on GaAs(001)-4×6. However, the upper distortion is stronger. There is also evidence of alloy formation at the interface involving the underlying Pd with the thickness of the alloy region being 2–2.5 ML.

The valence of Ru at the Mn sites in Pr_0.5Sr_0.5MnO₃ has been studied using Ru K- and L_III-edge x-ray absorption near edge structure (XANES) spectroscopy. In comparison with XANES of tetravalent and pentavalent ruthenates, it was found that the Mn-site doped Ru is mainly in tetravalent state with a small amount of pentavalent Ru. This result indicates that the change of carrier density with Ru doping is not sufficient to induce the drastic enhancement of ferromagnetism observed in transport properties of Ru-doped Pr_0.5Sr_0.5MnO3. The mixed valence state of doped Ru suggests that 4d orbitals of Ru are involved in electronic transport of the Mn³⁺-O-Mn⁴⁺ network with the valence fluctuation Ru⁵⁺ + Mn³⁺ ↔ Ru⁴⁺ + Mn⁴⁺. The prime role of Ru has been discussed in terms of Mn valence change and magnetic interactions between Mn and doped Ru ions.

Information about the local structure of amorphous carbon (a-C) films was obtained by comparing soft x-ray absorption spectra in the CK region of sputtered a-C films to reference carbon compounds such as hydrofullerene (C₆₀H₃₆), highly oriented pyrolytic graphite (HOPG), and carbon black. The spectra of the a-C films exhibited fine structures, which consisted of at least different six portions. Comparing the spectral features of the a-C films with the reference compounds and the spectral analysis by discrete variational (DV)-Xα molecular orbital calculations indicated that the fine structures of the a-C films are due to a hybrid of sp² and sp³ carbon atoms.

Glancing angle fluorescence XAFS analysis of Ta and Ti oxide thin films, which were obtained by oxygen gas cluster ion beam assisted deposition techniques (GCIB), was made to analyze the valence states and the structures of the 'amorphous' thin films at atomic level. Glancing angle XAFS measurement was made for Ta L₃-edge of the Ta oxide thin films and Ti K-edge of the Ti oxide thin films with 200 nm thickness, respectively, using the detection method of electron yield by conversion with He flow gas counter (CEY) at the beam line BL01B1 in the SPring-8. The Ta L₃-XANES results indicate that the assistance of the oxygen GCIB leads to the higher oxidation state of the Ta atom. The Ta L₃ and Ti K EXAFS results suggest that these metal oxide films obtained by the oxygen GCIB assisted deposition techniques have amorphous-like structure.

Structures and electronic states in the ground state of endohedral fullerence are investigated by XAFS analysis and XANES spectrum. The distances between the Eu ion and the neighboring C atoms show clearly that the Eu ion is inside the C₆₀ cage. The endohedral element, Eu, in C₆₀ is located away from the central position of C₆₀ cage by 1.4 Å. We show the detailed location of the Eu ion in the C₆₀ cage by XAFS and the first principles calculation. The perturbation theory indicates that the distortion of C₆₀ cage and the shift of the Eu ion are attributed to electron-nuclear interaction, pseudo-Jahn–Teller type interaction. XANES spectrum of Eu L_III-edge shows that the valence of the Eu ion is close to +2. The electron configuration is thus f⁷, showing the total symmetry (A_1g) of I_h group. The details of the structures and the electronic states will be discussed with both the experimental and theoretical results.

The near-edge fine structure of the F 1s absorption spectra of 3d metal fluorides was studied for the first time with high energy resolution. The spectra of these, the most ionic compounds of the 3d atoms, are analyzed comparing with the F 1s absorption spectrum of the molecular TiF₆²⁻ anion in solid K₂TiF₆. The latter spectrum was afore interpreted considering the fluorine spectra of the molecular PF₆⁻ anion in a KPF₆ crystal and of the gas-phase SF₆ molecule. The low-energy empty electron states in the 3d metal fluorides are shown to be formed due to covalent mixing of the metal 3d and fluorine 2p electron states.

The electronic and structural properties of Ru oxides were investigated by utilizing x-ray absorption spectroscopy (XAS). We estimate the valence of Ru in perovskite ruthenium oxides by XAS measurements. XAS measurements were carried out at room temperature around Ru K-edge. The valence of Ru in A₂(A = Ba, Sr)LnRuO₆ and A(A = Ca, Ba, Sr)RuO₃ was 4+. The valence of Ru in Ln₃RuO₇ was 5+. The valence of Ru in PbRuO₃ showed an intermediate value between 4+ and 5+. We calculated XAS spectra around the Ru K-edge by FEFF 8.0. Theoretical calculation reproduced the experimental spectra. We analyzed XAS spectra and obtained information of local structure. The bond length between Ru and O was consistent with the results of neutron diffraction.

The local order around K for K(CF₃SO₃) doped Siloxane-Poly(propyleneoxide) hybrids at different doping concentration was investigated by x-ray absorption spectroscopy (EXAFS and XANES) at the potassium K-edge. The results indicate that the use of HCl as hydrolytic catalyst for gelation induces the precipitation of KCl. The ionic conductivity is strongly related to the presence of oxygen atoms as first neighbours around potassium and to the amount of KCl precipitate.

On the basis of the first successful determination of the solvation structure of 1-bromonaphthalene (BrNaph) in supercritical xenon (sc-Xe) fluid (BrNaph/sc-Xe), we measured bromine K-edge fluorescent XAFS of bromobenzene (BrBz) doped in supercritical xenon (BrBz/sc-Xe), in an attempt to study the detailed characteristics of the solvation structure in supercritical fluids. Observed spectra of BrBz/sc-Xe showed obviously different pattern from that of BrBz liquid and that of BrBz/Hexane in the near-edge region. The small peak at 13 470 eV which appeared in the case of BrBz liquid was not observed in sc-Xe, and the broad peak around 13 490 eV was deformed especially at the higher energy side. On the basis of these spectral changes, we tentatively concluded that the local structure in BrBz liquid was destroyed in sc-Xe and a new solvation structure was formed. Theoretical calculation is now being planned.

We have investigated the initial stages of growth and relaxation of ZnO grown on {110} (a-sapphire) films ranging from 2.5 to 100 nm in thickness. A significant feature of this process is the change in symmetry in going from the twofold symmetry of the a-sapphire surface to the six-fold symmetry of ZnO. Asgrown films were investigated by atomic force microscopy (AFM), high-resolution x-ray diffraction, and polarized XAFS. AFM measurements indicated planar growth even from the earliest stages of epitaxy reflective of the long surface diffusion length of Zn. High-resolution x-ray diffraction measurements demonstrated resolution-limited (0002) rocking curves for films up to 30 nm thick (early growth) upon which the onset of diffuse scattering was observed, eventually coming to completely dominate for films thicker than 100 nm (late-growth). Polarized XANES and EXAFS measurements were performed on the Zn edge to elucidate structural changes from early to late-growth. Analysis of EXAFS data indicated an anisotropic accomodation of misfit with large in-plane bond rotations and with only a slight outward relaxation of the ZnO lattice along the [0001] direction. Electrical measurements indicate that the electron concentration in this initial layer is degenerate.

In SiO₂-GeO₂ glasses submitted to high pressure conditions, germanium atoms undergo a coordination change from four to six on a pressure-range depending on the composition. In the transition region, the possibility of having a mixture of tetrahedra and octahedra for Ge instead of the intermediate fivefold coordination state has been studied. Through comparison of the informations extracted from XANES and EXAFS, the model of a mixture of IV and VI coordination states, with a possible small amount of fivefold coordinated Ge appearing on the compression, is favoured.

Soft x-ray excited optical luminescence (XEOL) of silica glasses was studied with respect to the excitation x-ray energy (near the Si K-edge) and irradiation time. The luminescence spectra showed emission bands at 3.1 eV and 2.7 eV, assigned to B_2β and B_2α oxygen deficient centers in silica glasses, and the luminescence yields of these bands changed drastically before and above the Si K-edge. Si K-edge photoluminescence yield (PLY) spectrum of the band at 3.1 eV was similar to Si K-edge XANES spectrum recorded in the photocurrent mode for the same silica sample, except for the negative edge jump in the PLY spectrum.

The time evolutions of the band intensity at 3.1 eV were also investigated under the excitation by soft x-ray below and above Si K-edge. The band intensity in both cases decreased slightly with the irradiation. These results indicate that a part of B_2β centers in the silica glass probably changed to other types of oxygen deficiencies by the electron excitation effect. In the early stage of the irradiation, a rapid increase in the intensity of the 3.1 eV band was also observed, indicating that soft x-ray irradiation produced luminescence sites such as B_2β centers.

The adsorption site of sodium atoms deposited onto a clean TiO₂(110) surface has been determined by EXAFS. The best result is obtained for an 'in-between' site where the sodium is bound to two bridging oxygen atoms at 2.25 Å and one in-plane one at 2.40 Å in full agreement with DFT calculations. At higher coverage the site becomes a hollow site where Na is equidistant to the three oxygen atoms at 2.30 Å.

The position and shape of x-ray absorption discontinuities have been used to deduce structural and chemical bonding information on model compounds of thallium and its superconducting cuprates. The L x-ray absorption spectra were recorded on a Rigaku x-ray Spectrometer and monochromatized using a flat crystal of Si (1,1,1). The background subtraction was done using Victoreen function. The normalized absorption coefficient is plotted as a function of x-ray photon energy. It is observed that the XANES of L_I edge has fewer features as compared to those of L_III edge. The L_II edge spectra of thallium are similar to L_III edge spectra. The L_III absorption discontinuity of thallium splits into three components whereas no splitting is observed in L_I edges. Thallium L_III edge spectra show a single absorption peak for monovalent compounds whereas in trivalent compounds a weak peak followed by a shoulder on rising absorption which culminates into a strong absorption peak. The important difference between the spectra of monovalent and trivalent compounds is the shift in the inflexion point energy of L_III edges and a shift of the main absorption maximum. The x-ray absorption spectra of superconducting cuprates show similarities with the spectra of Tl₂O₃ suggesting the presence of Tl³⁺ ions in octahedral configuration in these cuprates.

This study combining x-ray diffraction and x-ray absorption spectroscopy reveals the variation of the lattice parameters a and c and the atomic position parameter z(Sn) of tetragonal stannous oxide SnO under pressure up to 10 GPa. The observed strong elastic anisotropy of the SnO crystal can be attributed to its layered structure. The axial ratio c/a decreases from 1.27 to 1.16 whereas the position parameter z(Sn) increases from 0.237 to 0.269.

The electronic structure of Mn/ZnO system has been invesigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage Θ_Mn ⩽ 4 ML. Photoemission spectra taken near the Mn3p–Mn3d absorption edge after each deposition step show resonant enhancement of Mn3d states within 10 eV of the Fermi edge. The experimentally deduced partial Mn3d density of states for Θ ⩾ 1.2 ML shows at least three features: a major Mn3d structure at 3.8–4.5 eV below the Fermi edge, a valence structure at lower binding energy (1–3 eV) and a broad satelite in the 5.5–9 eV range. The branching ratio of satellite/main structure increases with depostion from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 °C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surfaces as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4 eV, which shows that at least two manganese states are observed in the Mn–ZnO interface region.

The luminescence of a prototype gold(I) compound, PPh₃AuCl, which is a building block compound for many light emitting organo-gold complexes and polymers, has been studied by the X-ray Excited Optical Luminescence (XEOL) technique in conjunction with the X-ray Absorption Fine Structures (XAFS) at the C and P K-edge as well as the Au M_5,4-edges. We present the site and excitation channel specificity of XEOL and its chemical implications.

X-ray absorption spectroscopy was used to study the local structure and chemical bonding of elemental phosphorus. Three allotropes of this element exist in the solid state. The most common of these is the amorphous red phosphorus. The other two are crystalline: white phosphorus and black phosphorus. In the gas phase tetrahedral P₄ molecules are stable up to ∼ 800 °C. At higher temperatures P₂ molecules become dominant.

Theoretical P(1s) and P(2p) XAFS spectra of gaseous and solid state phosphorus were calculated by ab initio FEFF and GSCF3 methods. These were compared and the spectral features were related to structural and electronic properties of the different allotropes of elemental phosphorus. The calculation results were then used to explain the features observed in the experimental P(1s) and P(2p) spectra of red phosphorus that were measured using synchrotron radiation.

In this work, we analyze and correlate information obtained from XANES, EXAFS and NMR on a SiO₂ aggregate attacked by Alkali Silica Reaction (ASR). EXAFS and XANES results enable local order evaluation during the amorphization process within the aggregate. NMR results show the presence of amorphous and crystalline phases of silica during ASR attack. Besides, theoretical simulations of XANES spectra were performed and the atomic structure that generates the peak located 8 eV above the white-line (feature C in the text) was identified. The results lead us to deduce a change in the local order around silicon.

Pressure-induced scheelite-to-wolframite structural phase transition in SrWO₄ was studied using two complementary techniques—x-ray absorption spectroscopy and x-ray diffraction (XRD). In situ XRD and W L₃-edge EXAFS measurements were performed using the synchrotron radiation. The experiments were done at room temperature in the pressure range from 0 to 30 GPa using the diamond anvil cell. The XRD results unambiguously show that SrWO₄ transforms from the tetragonal scheelite phase to the monoclinic wolframite-type phase at about 11.7 GPa. Locally this transition appears as a change of the tungsten ions coordination from regular tetrahedral to distorted octahedral. The analysis of the EXAFS data suggests that tungsten ions displace from the centres of the tetrahedra by about 0.04 Å and some nearest oxygen atoms relax by about 0.23 Å.

Lithium intercalation and deintercalation in amorphous MoO₃-electrodes was investigated in situ using grazing incidence reflection mode x-ray absorption spectroscopy. Small changes observed in the near edge x-ray absorption spectra indicated that the Mo⁶⁺ ions are reduced by the electrochemical lithiation, leading to a formal Mo⁵⁺ oxidation state. Angle dependent experiments reveal that the intercalation is not complete for the applied conditions, i.e. the Li-ions are not homogeneously distributed in the entire volume of the amorphous working electrode. In addition, a certain amount of Li remains in the Mo-oxide electrode after a complete intercalation/deintercalation cycle. The results suggest that Li ions are accumulated at the electrode/electrolyte interface during both intercalation and deintercalation.

The local structures of semi-metal Sb have been studied by in-situ XAFS in the temperature range of 298 and 913 K. The radial structural functions of Sb atoms reveal that the local structure of the pre-molten Sb (893 K) is similar to that of crystalline Sb (298 K), except the increase of thermal disorder degree. With the temperature increasing up to 913 K, the position of the first peak located at 2.63 Å in the liquid Sb is kept the same as that in the pre-molten Sb, while the intensity of the first peak is strongly reduced by about 30% during the solid-liquid transition. This feature indicates that the melting results in a large increase of disorder degree of the liquid Sb, and that there exists covalent bonded clusters (Sb)_n in the liquid Sb (913 K).

The nature of passive film grown on the bulk surface of Fe–20Cr alloy in a pH 8.4 boric-borate buffer was investigated with in situ synchrotron x-ray absorption spectroscopy. The main electrochemical test method was potentiostatic polarization and various potentials were applied from −1.0 V to 0.6 V vs saturated calomel electrode (SCE). X-ray absorption data from the passive film formed in the boric-borate buffer were collected from an in situ reflection x-ray absorption spectroscopic experiment in a grazing-incident geometry that is suitable for investigating the nanometer-thick passive film. It was observed in the Fe K-edge XANES (X-ray Absorption Near-Edge Structure) region that the Fe absorption edge moved from the absorption edge of metal Fe to that of Fe oxide as the applied potential increased. It was observed from an analysis of the Radial Distribution Function (RDF) from Fe K-edge EXAFS (Extended X-ray Absorption Fine Structure) data that the Fe–Fe bond intensity of the first shell decreased and Fe–O bond intensity increased as the applied potential increased. The RDF of the Fe oxide is consistent with γ-Fe₂O₃.

X-ray absorption fine structure measurements at zinc K-edge in the corrosion product of super plastic processed zinc doped magnesium alloy has been performed to clarify the corrosion mechanism. The XANES spectra and the radial distribution functions obtained from Fourier transformed EXAFS oscillations of the corrosion product of zinc doped magnesium alloy and reference compounds of ZnO, zinc carbonate (2ZnCO₃·Zn(OH)₂·H₂O), ZnCl₂ and zinc foil suggest that the local structure of Zn compound in corrosion product is close to that of zinc carbonate.

X-ray K-absorption studies have been carried out on Al–Mn system comprising Al₉₀Mn₁₀, Al₈₈Mn₁₂, Al₈₆Mn₁₄, Al₈₄Mn₁₆, Al₈₂Mn₁₈ and Al₈₁Mn₁₉ samples. These samples have been characterized by x-ray diffraction (XRD) studies which support the formation of icosahedral phase. The x-ray K-absorption discontinuities in case of the Al–Mn system have been found to be shifted towards the high energy side with respect to the K-absorption edge of pure metal Mn, which indicates the behaviour of manganese atom as the cation. The x-ray absorption chemical shifts suggest a covalent bonding. The studies also indicate that with the increase in Mn concentration chemical shifts also increase.

We have attempted to correlate the values of the electron to atom ratio (e/a) with the chemical shifts (ΔE). The nature of relationship between e/a and ΔE is quite similar to that between ΔE and Mn concentration. Further, we have estimated the density of states at the Fermi level D(E_F) for these samples and plotted them against chemical shift values. Extrapolation from this graph between D(E_F) and ΔE indicates a D(E_F) value for Al metal which is quite near to the actual value for Al metal. These studies establish the existence of a pseudo gap in the case of presently investigated Al–Mn samples. The present studies also support our assumption of assigning the chemical shift values to the Fermi level in the case of Al–Mn system under present investigation.

X-ray K-absorption edges along with their extended x-ray absorption fine structure (EXAFS) have been recorded using a laboratory XAFS spectrometer for the Co(II) imidazoles viz., Co(etImz)₂Cl₂, Co(iprImz)₂Cl₂, Co(tvImz)₂Cl₂, Co(vImz)₄Cl₂, Co(vImz)₄(SCN)₂, Co(tvImz)₄Cl₂, and Co(tvImz)₄(SCN)₂. The chemical shifts for these samples have been reported and the present studies reveal that the anions in Co(ligand)₄Cl₂/(SCN)₂ do not interact strongly with the metal ion. The studies further show that the complexes have tetrahedral structure in which anions Cl₂/(SCN)₂ remain outside the first coordination shell in Co(ligand)₄Cl₂/(SCN)₂ type complexes. The total phase shifts δ₁ and phase parameters β₁ for these samples have been estimated using the modified graphical method for the determination of bond distances. The values for phase parameter β₁ explain the dominance of backscattering in the various complexes studied.

The structural change and charging process for Li_1−xNi_0.5Mn_0.5O₂ were determined by x-ray diffraction and XAFS measurement. XAFS has been employed to investigate the change in electronic structure of cathode material. As the cell charged, the Ni K-edge XANES spectra showed chemical shift towards higher energy, while Mn K-edge showed no significant shift. Divalent nickel metal is oxidized to trivalent with Li-deintercalation, in association with the phase transition from hexagonal (R3m) to monoclinic (C2/m).

The magnetic properties of a few atomic Pt layers on a 15 nm thick Co film were studied by x-ray magnetic circular dichroism spectroscopy at the Pt L_2,3 edges. The spin and orbital magnetic moments of the Pt 5d electrons were separated using the magneto-optical sum rules. The Pt magnetization profile as a function of distance from the Co–Pt interface was determined using data from a series of films with various Pt thicknesses. This magnetization profile was approximated by an exponential function with a decay length of 0.41 nm, which characterizes the effective range of the magnetic coupling between Co and Pt. The total magnetic moment of a Pt atom at the interface was 0.7 μ_B/atom including a 13% orbital moment. This is discussed in the context of the thermal stability of magnetic recording media capped with a thin layer of Pt.

The effect of CO adsorption on the magnetic easy axis of Co/Pd(111) magnetic thin films has been studied by C 1s x-ray photoelectron spectroscopy (XPS) and Co L-edge x-ray magnetic circular dichroism (XMCD) in absorption spectroscopy. We found by the XMCD measurements that the CO adsorption at 200 K induces the spin reorientation transition of a 4–6 monolayer (ML) Co thin film, but it does not cause spin reorientation at 300 K. Simultaneous XPS measurement showed that the C 1s spectrum has a single peak at 285.8 eV at 300 K, while it has an additional shoulder at 285.3 eV at 200K. The main peak is associated with the CO atop adsorption, and the shoulder might be ascribed either to bridge or hollow site adsorption. Temperature and CO coverage dependences of XMCD and C 1s XPS spectra reveal that the bridge or hollow site CO adsorption is responsible for the spin reorientation of the Co thin film. This is the first direct observation to correlate the magnetic anisotropy of a magnetic thin film with the molecular adsorption site.

We report on XMCD measurements at the L_2,3 edges of the early 3d transition metals, Ti, V and Cr, polarized by Fe. In contrast to the classical ferromagnets Fe, Co and Ni, the XMCD spectra reveal a complex and detailed fine structure. We analyze the experimental data with the help of full-relativistic ab initio calculations of the x-ray absorption cross section μ(E) that provide the energy-dependent XMCD spectrum and the correlated magnetic moments μ_s and μ_l. We demonstrate that the use of the so-called integral sum-rules, which interrelate certain areas of the XMCD spectra to μ_s and μ_l, yield erroneous results for the early 3d elements due to 2p-3d core hole correlations in L_2,3 absorption spectra.

We report on a polarized x-ray absorption spectroscopy study, combining experimental measurements and ab initio calculations, of La_0.7Sr_0.3MnO₃ films, epitaxially grown on tensile and compressive substrates. Measurements show significant modifications in the coordination shell around manganese atoms in the film plane for both substrates. We show that biaxial strain is locally accommodated in the coordination shell, by distortion of the MnO₆ octahedron, without change in the tilt angle. The modifications of the near edge spectra were correlated to modification in the average Mn–O bond distance and distortion of the MnO₆ octahedra. This distortion tending to localize the charge carriers may account for the decrease of the Curie temperature observed in thin films with respect to bulk systems.

To study pressure-induced ferromagnetic state in Mn₃GaC perovskite, we have performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ga K-edge under high pressure up to 29.4 GPa at room temperature. Ga K-edge XMCD was observed under pressure ranging from 4.5 to 29.4 GPa and results indicate that the Ga atom is magnetically polarized under high pressure. From the XMCD spectral profile, it is suggested that the pressure-induced ferromagnetic state has a canted ferromagnetic structure.

The geometric and electronic local structure of LaMnO₃ across the cooperative Jahn–Teller (JT) transition at T_JT = 750 K has been studied by means of X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) at the Mn K-edge. XANES spectra, as a function of temperature, do not show significant changes either in the pre-peak structures or at the absorption edge indicating similar electronic local structure for the Mn atom above and below T_JT. Analysis of the EXAFS spectra shows that dynamical tetragonal JT distortion of the MnO₆ octahedron is also present above T_JT. The structural transition is explained in terms of an orientated ordering of tetragonal distorted octahedral complexes. Above T_JT, the e_g electron jumps between the three degenerate vibronic states being localized and ordered below the transition.

Co doped TiO₂-anatase is a promising candidate for a room-temperature ferromagnetic semiconductor. XAFS measurements have been used to investigate the local Co environment and Co valence for several Co-anatase films. The samples were grown on LaAlO₃ (001) by oxygen plasma assisted molecular beam epitaxy and on SrTiO₃ by atomic oxygen assisted MBE. Co concentrations were about 5%. The measurements were made at the PNC-CAT bending magnet and undulator beamlines at the Advanced Photon Source. For the films on LaAlO₃, the near edge clearly shows the presence of only Co(2+), and no evidence for metallic Co, while the films on SrTiO₃ showed significant metallic Co. Analysis of the extended fine structure for the LaAlO₃ films finds that the Co substitutes for Ti with some distortion of the lattice. Both in-plane and out-of-plane Co–O bonds are expanded from the Ti–O bonds in anatase. The in-plane bonds are expanded approximately twice as much. A deficit in the oxygen coordination number suggests a correlation of oxygen vacancies with Co sites.

A systematic study of the x-ray magnetic circular dichroism at the L₃ edge is presented for Gd and Tb single crystals in the extended energy range (MEXAFS). The investigation of the dichroic signal in this energy range is especially interesting for rare earth metals because the relative intensity of the magnetic EXAFS to the near edge signal (XMCD) is much larger compared to 3d transition metals. This is because the MEXAFS for the rare earth elements is essentially proportional to the total 4f magnetic moment, whereas the XMCD is dominated by dipole transitions to the spin-dependent 5d densities of states only. The temperature dependence of the magnetic EXAFS originates both from spin fluctuations and lattice vibrations. We present a new procedure to separate these contributions by modeling the absorption coefficients μ⁺(E) and μ⁻(E) for right and left circularly polarized x-rays, by the energy shifted experimental spin-averaged spectra. The temperature dependence of the MEXAFS can then be described by a temperature-dependent energy shift ΔE(T) which is proportional to the temperature-dependent magnetization M(T). Furthermore, multiple and single scattering contributions in the MEXAFS are separated by comparison of the experimental data to ab initio calculations using the FEFF8 code.

X-ray resonant scattering experiments at (002) and (006) forbidden Bragg reflections were performed on Fe₃O₄, MnFe₂O₄ and CoFe₂O₄ single crystals. The intensity of these reflections in Fe₃O₄ shows three characteristic features as a function of energy. A pre-peak resonance related to dipolar-quadrupolar transitions coming from the tetrahedral Fe ions and a main resonance at the absorption edge and the energy-extended oscillating part ascribed to the anisotropy of the octahedral Fe ions. X-ray resonant scattering experiments on MnFe₂O₄ (normal spinel) and CoFe₂O₄ (inverse spinel) ferrites verify experimentally the origin of these resonances, the main peak is caused by the dipole transition of the octahedral site iron and the pre-edge peak is due to the dipole-quadrupole transition of the tetrahedral site iron, independently of the formal valency or chemical specie. These experimental results show that anisotropic tensor susceptibility (ATS) scattering cannot be simply considered as a direct proof of orbital ordering.

Permanent magnets based on Sm₂Co₁₇ are of significant technological interest due to their high coercivities and elevated Curie temperatures. In this paper we examine the local environment of Zr-doped Sm₂Co₁₇. The presence of Zr in Sm₂Co₁₇-based magnets causes the formation of hexagonal Sm₂Co₁₇ lamellae in the microstructure in the commercial materials. These lamellae serve as diffusion paths, enabling the development of good magnetic properties. While it is presumed that the Zr enters the lattice into either the Sm or Co dumbbell sites, there is, to date, no direct evidence of this assumption. In this paper, we present evidence of how the Zr does substitutes into the Sm₂Co₁₇ lattice. We discuss the implication of this result on the magnetic properties and grain structure of the Zr-doped material.

Spin-dependent x-ray absorption near edge structure (XANES) spectra measured by selectively monitoring of the Mn K-beta emission while scanning the excitation energy through the Mn K absorption edge were analyzed. The method of calculation is based on a combination of self-consistent spin-polarized calculation of muffin-tin potential and a full multiple scattering theory for interpretation of x-ray absorption. This approach allows to separate influence of dipole transition matrix elements and density of empty electronic states on spin-dependent XANES. It is found that matrix elements affect the splitting between spin-up and spin-down spectra only near the absorption threshold, while differences in densities of states slightly shift spectra in the region 35–55 eV above the main edge. Effects of multielectron term dependent broadening of spin-dependent XANES spectra and different mean free paths of photoelectrons with spin-up and spin-down in ferromagnetic phase were taken into account. It is shown that these factors also contribute to the splitting of spectra with different spin directions near the absorption threshold.

Soft x-ray magnetic circular dichroism (MCD) and absorption spectra (XAS) were measured at the Fe L_2,3-edges and the Dy M_4,5-edges for a family of dysprosium iron garnets. The Fe ions sit in either O_h symmetry sites or T_d symmetry sites in Dy₃Fe₅O₁₂. Only Fe ions in the O_h sites are substituted with In ions in Dy₃Fe_4.25In_0.75O12 and only Fe ions in the T_d sites are substituted with Ga ions in Dy₃Fe_4.25Ga_0.75O₁₂. The XAS spectrum profiles of the three-dysprosium iron garnets are very similar. The MCD signals of both the Fe L_2,3-edges and the Dy M_4,5-edges of Dy₃Fe_4.25Ga_0.75O₁₂ are similar to that of Dy₃Fe₅O₁₂, but Dy₃Fe_4.25In_0.75O₁₂ is remarkably different. The results directly show that the spin moment of Fe in the Td sites play a major role in determining the total magnetization of Dy₃Fe₅O₁₂.

In this work, geometric structures for TM-doped (TM = Mn and Fe) ZnO film grown by combinatorial laser molecular beam epitaxy (CLMBE) were investigated using fluorescence EXAFS measurement. The EXAFS analysis has revealed that the majority of TM ions heavily doped in ZnO ([Mn] ∼ 20% and [Fe] ∼ 1%) substituted the Zn atoms in ZnO lattice.

We studied the feasibility of magnetic circular dichroism (MCD) in the hard x-ray region for determining 4f magnetic moments by measuring the temperature dependence of MCD spectra at rare earth L₂-edge in systems of rare earth iron garnets (R-IG) for R = Gd, Dy and Sm. Two components arising from the magnetization of the Gd and Fe sublattices, which were combined into the MCD spectrum of Gd-IG, were separatively deduced. For Dy- and Sm-IG, we successfully obtained the temperature dependence of the MCD component that comes from only R sublattice magnetization under the assumption that the MCD spectra of the series of R-IG contain the same contribution of the iron sublattice.

Polarization-dependent x-ray absorption fine structure together with x-ray diffraction have been used to study the local structure in SrTiO₃ thin films grown on Si(001). Our data indicate that an interfacial polarization of the SrTiO₃ layer by the Si substrate results in a tetragonal distortion of the SrTiO₃ unit cell.

Films of cobalt-doped titanium dioxide (Co_xTi_1−xO_2−δ) can be stabilized in the thermodynamically unfavorable anatase phase if they are grown on appropriate substrates. We performed X-ray Absorption Spectroscopy (XAS) measurements at the oxygen, titanium, and cobalt edges of PLD grown samples. Our data shows the success of this substrate-induced stabilization of the anatase phase occurs only at elevated temperatures (∼ 700 °C or more) and elevated oxygen partial pressures (∼ 1 × 10⁻⁵ Torr or more). The effects of post annealing in vacuum are also considered.

We use XMCD at the L_2,3 edges of iron to analyze the site-specific magnetic contributions of ions in nanoparticles of maghemite, γ-Fe₂O₃. Maghemite is the oxidized form of magnetite Fe₃O₄. We report results of the study of the magnetic order on tetrahedral and octahedral magnetic sublattices in γ-Fe₂O₃ nanoparticles as a function of the applied magnetic field. Magnetic contributions of Fe³⁺_Oh and Fe³⁺_Td are determined using the Ligand Field Multiplet theory. It is found that when the external field decreases, the magnetic contribution of Fe³⁺ ions on octahedral sites is significantly reduced by comparison to the contribution of Fe³⁺ ions on tetrahedral ones. This shows that a higher degree of canting exits on octahedral sites.

We report X-ray Absorption Fine Structure (XAFS) measurements of the colossal magneto-resistance (CMR) samples La_0.79Ca_0.21MnO₃ and La_0.7Ca_0.3MnO₃ at high magnetic fields. For T near T_c, the width parameter of the pair distribution function, σ, decreases significantly as the applied magnetic field is increased. For a given magnetization, M, the decrease in σ² from the disordered polaron state is the same, irrespective of whether M was achieved through a change in temperature or the application of an external magnetic field. This universal behavior can be modeled as a quadratic function of magnetization, and suggests a new model for the magnetization process.

We have measured Mn K-edge magnetic EXAFS for Ni_0.76Mn_0.24 alloy. The 2nd peaks in the Fourier transform attributed to Mn-Mn pairs in the ordered phase are enhanced in comparison with those in non-magnetic EXAFS. This result suggests that some Ni atoms in the 2nd shell are replaced by Mn atoms, which have large magnetic moment in comparison with Ni atoms, due to heat-treatment induced atomic ordering. Semi-relativistic theoretical calculations well explain the observed magnetic EXAFS. We estimate the ratio of the magnetic moments of Ni to Mn atom in Ni-Mn alloy, within a single scattering limit.

Fe₈ clusters are molecules which show quantum spin tunneling at very low temperature. They have eight iron ions that are six-fold coordinated and magnetically coupled through oxygen bridges. The net magnetization (M_s = 20 μ_B per molecule) results from competing antiferromagnetic interactions between the Fe³⁺ ions (S = 5/2). Because of the structural anisotropy of these molecules, the magnetization curve presents a hysteresis loop with staircases below 2 K. The staircases of the hysteresis loop are due to the quantum spin tunneling, which is temperature dependent for 400 mK < T < 3 K and temperature independent below 400 mK. Using a ³He–⁴He dilution refrigerator, we have recorded XMCD spectra at iron L_2,3 edges at 300 mK for this molecule. It has been possible to record an XMCD remnant signal, without magnetic field applied, on these high spin molecules. XMCD coupled with Ligand Field Multiplet calculations has allowed to determine the spin and orbit magnetizations of Fe³⁺.

The elements-specific magnetizations of Co/Cu/Ni trilayers are studied near their Curie temperature by x-ray magnetic circular dichroism. Small magnetic fields are applied during the measurements to rule out the formation of magnetic domains. The experiments confirm that the Curie temperature of the Ni magnetization is shifted up to ΔT_Ni ≈ 80 K in presence of an interlayer exchange coupling. In agreement with ab initio theory, we evidence the tail of the Ni magnetization in the trilayer.