Table of contents

The PDF is the preface of the proceedings volume of the 14th International Conference on X-ray Absorption Fine Structure (XAFS14) held in Camerino, Italy, 26–31 July 2009.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We discuss an efficient approach for calculations of optical to x-ray response based on a spectral function formalism which is implemented in an extension to the real-space Green's function code FEFF. This formalism avoids the need to compute wave-functions explicitly, and is applicable to arbitrary, aperiodic systems. Starting from the complex dielectric constant, the approach gives a number of linear optical constants, including the complex index of refraction the photoabsorption coefficient and energy-loss spectra over a very broad spectral range. These results provide a theoretical complement to standard tables and are useful in a variety of applications including ab initio calculations self-energy shifts, inelastic losses, mean-free paths, and stopping powers. For example, a many-pole self-energy model based on these results makes possible improved, parameter free calculations of various photon- and electron-spectra. The method is compared with experiment and with a pseudopotential-planewave Bethe-Salpeter Equation method.

We explore the convergence of the multiple scattering series by studying the spectral radius of the corresponding multiple scattering matrix. The energy variations of this spectral radius exhibit strong oscillations. These oscillations are shown to depend strongly on the electronic and crystallographic structure in the low energy regime. As the calculation of the eigenvalues of the multiple scattering matrix is very long, we devise a fast algorithm to approximate this spectral radius.

We present a detailed analysis of the pre-edge peak present in the Al K-edge XANES spectra of corundum (α-Al₂O₃) and diaspore (α-AlOOH), as measured at room temperature. This is achieved by XANES and DOS calculations performed using the density functional theory in a pseudopotential plane-wave framework. The XANES calculations carried out for the equilibrium atomic positions do not reproduce the pre-edge of corundum and partially reproduce it in the case of diaspore. It is shown that the electronic transitions occuring in the pre-edge involves the 3s empty states of the aluminium absorbing atom. The Al 3s states can be probed in the electric dipole approximation via a p-s mixing, which is possible only if the Al site is not centrosymmetric. Although Al does not occupy an inversion center in the two minerals under study, the p-s mixing is too weak to provide a pre-edge feature in good agreement with experiment. The deviation from centrosymmetry can be enhanced by the atomic vibrations. We develop a theory that takes into account the atomic vibrations directly in the calculation of the absorption cross section, based on the Born-Oppenheimer approximation. This theory is applied to corundum and diaspore and yields satisfactory results in the pre-edge region.

An overview is given of the interactions that determine the XANES spectral shapes of transition metal compounds. The interactions are divided into ground state effects, final state effects and transition effects. The metal L edges, metal K edges and ligand K edges are analysed with respect to these interactions. The importance of XANES is partly due to its wide versatility in measurement conditions. XANES spectra can be measured using a number of sample environments, ranging from vacuum to ambient pressures for soft x-rays and up to extreme conditions with hard X-rays. These in-situ XANES spectra can be measured with a spatial resolution of 10 to 30 nm. XANES spectral shapes can be used as resonant channels in resonant photoemission, resonant x-ray emission or resonant diffraction experiments. This gives rise to a large number of resonant techniques that also allow the detection of site, valence, spin and symmetry selective XANES spectra and/or XANES spectra revealing information with a resolution better than its lifetime broadening.

X-ray-absorption near-edge structures (XANES) at the transition metal (TM) L_2,3-edge of TiCl₄ and VOCl₃ are calculated by the all-electron configuration interaction (CI) method using fully-relativistic molecular spinors with density functional theory (DFT). The electronic excitation from molecular spinors mainly composed of ligand p atomic spinors to those of TM-3d spinors, i.e., the charge transfer, is included by taking additional electronic configurations in the CI. The effects of the ligand field and the charge transfer on the TM-L_2,3 XANES are investigated by an ab-intio method. The reduction of inter-electron interaction due to the covalent bonding between TM and ligand atoms has been found. The contribution of charge transferred configuration is small at the initial state of TM-L_2,3 XANES while the significant amount of charge transferred configuration is found at the final states. The spectral shapes of TM-L_2,3 XANES of both TiCl₄ and VOCl₃ are strongly modified by the charge transfer effects.

Using the recently developed multi-channel multiple scattering (MCMS) method we have calculated the x-ray absorption spectra (XAS) at the L_2,3-edge of transition metal compounds. The MCMS method is an ab initio scheme which combines an accurate description of the band structure of the material with a correlated many-electron wave function on the absorber atom. Thereby configuration interaction in the XAS final state, in particular multiplet effects, can be taken into account. In the present implementation, we use an electron-hole wave function and treat the interaction with all other electrons on a mean-field level. The calculated spectra agree well with experiment for the early transition metals (Ti,V), where the L2–L3 configuration mixing is particularly strong. We present a detailed study of titanium oxides with nominal Ti⁴⁺ ground state, namely rutile and anatase TiO₂ and perovskite SrTiO₃. The XAS spectra display a rich fine structure with marked differences between the three systems despite the almost identical octahedral coordination of the Ti atom. The calculated spectra are in excellent agreement with the experimental data of all three compounds. As an example for a late 3d-metal we have studied the L_2,3-XAS and the x-ray magnetic circular dichroism (XMCD) of iron. In agreement with recent time-dependent density functional studies, we find that also for the late 3d elements, the particle-hole description can yield satisfactory L3/L2 branching ratios and lineshapes of the isotropic XAS spectrum if the screened monopole term of particle-hole Coulomb interaction is properly taken account for. The XMCD spectra of the same calculation are, however, less good than both atomic multiplet and one-electron spectra indicating clear limitations for the application of particle-hole theories to late 3d elements.

A user friendly tool allowing the simulation of x-ray absorption near edge structure (XANES) spectra and Resonant X-ray Diffraction (RXD) peak intensity is necessary for many purposes. We present the actual developments of the FDMNES code which realizes this task in a mono-electronic approach. The code uses both the multiple-scattering theory and the finite different method in a fully relativistic frame, including thus the spin-orbit interaction. In diffraction, the resonant and non-resonant, magnetic and non-magnetic components are all included, allowing an easy use by non experts of the code. In the same idea, the automatic analysis of the unit cell (or molecule) symmetry greatly simplifies the user's work. Summation on and energy shift between the different absorption sites are automatically included. Comparison with experiment in order to fit parameters is also possible. The last advances with the self-consistent calculations are discussed. It is shown that within the multiple-scattering theory, using the muffin-tin approximation on the shape of the potential, the improvement is not high for non magnetic situation and limited to the pre-edge region. The improvements coming from the non-muffin-tin corrections are notably higher. More improvement results from self-consistency for the magnetic NdMg system. Various examples in oxides and metal in RXD and XANES are given showing the potentiality of the code. The fit procedure is applied in the magnetite low temperature phase case.

The present article is a brief critical review about the possibility of detecting charge and/or orbital order in transition-metal oxides by means of resonant x-ray diffraction. Many recent models of transition-metal oxides are based on charge and/or orbitally ordered ground-states and it has been claimed in the past that resonant x-ray diffraction is able to confirm or reject them. However, in spite of the many merits of this technique, such claims are ambiguous, because the interpretative frameworks used to analyze such results in transition-metal oxides, where structural distortions are always associated to the claimed charged/orbitally ordered transition, strongly influence (not to say suggest) the answer. In order to clarify this point, I discuss the two different definitions of orbital and charge orderings which are often used in the literature without a clear distinction. My conclusion is that the answer to the question of the title depends on which definition is adopted.

Conventional Kohn-Sham band-structure methods for calculating deep-core x-ray spectra typically neglect photoelectron self-energy effects, which give rise to an energy-dependent shift and broadening of the spectra. Here an a posteriori procedure is introduced to correct for these effects. The method is based on ab initio calculations of the GW self-energy using a many-pole model and a calculation of the dielectric function in the long wavelength limit using either the FEFF8 real-space Green's function code, or the AI2NBSE interface between the National Institute of Standards and Technology (NIST) Bethe-Salpeter equation solver (NBSE) and the ABINIT pseudopotential code. As an example the method is applied to core level x-ray spectra of LiF and MgAl₂O₄ calculated using (respectively) OCEAN, an extension of the AI2NBSE code for core level excitations, and the PARATEC pseudopotential code with the core-hole treated using a super-cell. The method satisfactorily explains the discrepancy between experiment and calculations.

Following our recent derivation of a Real Space Full-Potential Multiple-Scattering-Theory (RSFP-MST), we calculate the low-energy part of the K-edge absorption spectra of the transition metals of the first row of the periodic table using the Hedin-Lundqvist (HL) and the Dirac-Hara (DH) complex potentials, which are often used in the literature for this kind of calculations. In both cases the complex part is taken from the HL potential. Taking advantage of the fact that in the FP-MS scheme the Schrödinger Equation is solved exactly without approximations (within the limits of the l-truncation procedure in MST), we intend to test the ab initio validity of these optical potentials in cases that are borderline between the independent particle and the weakly correlated regime. Surprisingly enough, we find better agreement with experiments with the DH potential.

We present an accurate and efficient technique for calculating thermal X-ray absorption fine structure (XAFS) Debye-Waller factors (DWFs) applicable to crystalline materials. Using Density Functional Theory on a 3×3×3 supercell pattern of MnO structure, under the nonlocal hybrid B3LYP functional paired with Gaussian local basis sets, we obtain the normal mode eigenfrequencies and eigenvectors; these parameters are in turn used to calculate single and multiple scattering XAFS DWFs. The DWFs obtained via this technique are temperature dependent expressions and can be used to substantially reduce the number of fitting parameters, when experimental spectra are fitted with a hypothetical structure. The size of the supercell size limits the R-space range that these parameters could be used. Therefore corresponding DWFs for paths outside of this range are calculated using the correlated Debye model. Our method is compared with prior cluster calculations and with corresponding values obtained from fitting experimental XAFS spectra on manganosite with simulated spectra.

Metalorganic molecules like Fe-porphyrin or haemoglobin have been investigated in great detail in the past. Its importance is obvious and has been measured mostly with molecules in random orientation. Here we report on experiments of a single monolayer of Fe-porphyrin in UHV aligned flat on ferromagnetic Ni and Co films. NEXAFS with linear and circular polarization is the spectroscopy of choice; it is elementspecific and measures the electronic structure as well as the magnetism at once. For the flat oriented monolayer of porphyrin molecules we have measured the angular dependence of XAFS at the C and N K-edge and XMCD at the Fe L-edges. The paramagnetic Fe-spin is aligned with respect to the ferromagnetic substrate. This can be parallel or antiparallel. Also nonmagnetic substrates like Cu (100) plus an external magnetic field will align the magnetic Fe-moment. This altogether opens a huge field for switching the 3d-spin from parallel to perpendicular of the molecular plane, which in turn will modify the electronic transport properties and act as a single molecular switch.

X-ray magnetic circular dichroism(XMCD) spectra at the L_2,3 edges of mixed-valence rare-earth compounds in high magnetic fields are studied both theoretically and experimentally. The theoretical study is based on a new framework proposed recently by Kotani. The Zeeman splitting of 4f states, the mixed-valence character of 4f states, and the 4f-5d exchange interaction are incorporated into a single impurity Anderson model. New XMCD experiments in high magnetic fields up to 40 T are carried out for the mixed-valence compounds EuNi₂(Si_0.18Ge_0.82)₂ and YbInCu₄ by using a miniature pulsed magnet, which was developed recently by Matsuda et al. The XMCD data are taken at 5 K by transmission measurements for incident X-rays with ± helicities at BL39XU in SPring-8. After giving a survey on recent developments in the theory of XMCD spectra for mixed-valence Ce and Yb compounds, we calculate the XMCD spectra of YbInCu₄ at the field-induced valence transition around 32 T by applying the recent theoretical framework and by newly introducing at 32 T a discontinuous change in the Yb 4f level and that in the hybridization strength between the Yb 4f and conduction electrons. The calculated results are compared with the experimental ones.

A many-body relativistic theory to analyze X-ray Magnetic Circular Dichroism (XMCD) spectra has been developed on the basis of relativistic quantum electrodynamic (QED) Keldysh Green's function approach. This theoretical framework enables us to handle relativistic many-body effects in terms of correlated nonrelativistic Green's function and relativistic correction operator Q, which naturally incorporates radiation field screening and other optical field effects in addition to electron-electron interactions. The former can describe the intensity ratio of L₂/L₃ which deviates from the statistical weight (branching ratio) 1/2.

In addition to these effects, we consider the degenerate or nearly degenerate effects of core levels from which photoelectrons are excited. In XPS spectra, for example in Rh 3d sub level excitations, their peak shapes are quite different: This interesting behavior is explained by core-hole moving after the core excitation. We discuss similar problems in X-ray absorption spectra in particular excitation from deep 2p sub levels which are degenerate in each sub levels and nearly degenerate to each other in light elements: The hole left behind is not frozen there. We derive practical multiple scattering formulas which incorporate all those effects.

The effective spin sum rule is reviewed with a detailed analysis of the various sources for errors and deviations of this widely used X-ray Magnetic Circular Dichroism (XMCD) tool. The simulations confirm that the final state effects of the core level spin-orbit coupling and the core-valence exchange interactions (multiplet effects) are linearly related with the effective spin sum rule error. Within the ligand field multiplet approach, we have analyzed these effects, in combination with the interactions affecting the magnetic ground state, including the crystal field strength and the 3d spin-orbit coupling. We find that for the late transition metal systems, the error in the effective spin moment is between 5 and 10%. Because of the potentially large <T_z> value, the spin moment can not reliably be determined for all systems other than Ni. The error for 3d⁴ systems is very large, implying that, without further information, the derived effective spin sum rule values for 3d⁴ systems have no meaning.

A valence fluctuating phenomenon, which is one of the most interesting subjects in strongly correlated electron systems, has been studied theoretically in EuNi₂(Si_0.18Ge_0.82)₂, in which the field-induced valence transition from a nonmagnetic Eu³⁺ state (4f⁶) to a magnetic Eu²⁺ state (4f⁷c¹) was observed at around 40 Tesla by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at Eu L-edges. Here, c denotes a hole in a conduction band. Both XAS and XMCD in fields exhibit two peaks corresponding to the two valence states, although one of them is nonmagnetic. In this paper, we propose a model to explain the field-induced valence transition, in which the hybridization between the 4f⁶ state and the 4f⁷c¹ state plays an essential role. Comparing XAS and XMCD calculated with experimental data, we find that XAS and XMCD provide us with detailed microscopic information on the mixed valence state through the polarized 5d electrons. Finally, we demonstrate how effective XAS and XMCD are for studying such mixed valence phenomena.

We have studied Bi L-edge X-ray magnetic circular dichroism (XMCD) of Bi substituted Gd iron garnet (BiGd-IG) by using the relativistic multiple scattering calculations. BiGd-IG has giant magneto-optical response with substituted Bi. The XMCD analysis is suitable to understand the interesting behavior; it is important to understand the local magnetic and electronic structure around absorption atom Bi. Comparing the experimental spectra, we find that the proportion of magnetic atoms to nonmagnetic ones around Bi strongly influence the Bi XMCD spectra. We also investigate the effects of the spin polarization of the Bi 6p states.

We have measured Ti L_2,3-edge X-ray magnetic circular dichroism (XMCD) spectra of Co doped anatase TiO₂ (Co_0.05Ti_0.95O₂), where nonzero XMCD spectra have been observed even at Ti L_2,3-edge. In order to understand the reason why the XMCD signals are observed at Ti L_2,3-edge, we have applied the relativistic multiple-scattering approach to the analyses of the observed XMCD spectra. The results show that the Ti L_2,3-edge XMCD spectra are dominated by the spin-dependent exchange scatterings on the spin-polarized Co sites. We find a good agreement with the observed L₃ XMCD spectra. The calculated XMCD spectra are rather sensitive to the spin moment on the X-ray absorbing Ti. We conclude that the spin moment on Ti site is very small and antiparallel to that on Co. The calculated results also show that the observed Ti L_2,3-edge XMCD signals arise from the Ti atoms within about 4 Å from spin-polarized Co atoms.

L-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in high magnetic fields up to 40 T using a pulsed magnet. XMCD spectrum of Eu in a typical valence fluctuating compound, EuNi₂(Si_0.18Ge_0.82)₂, shows a characteristic two peak structure, reflecting the valence fluctuation. However, in another valence fluctuating compound, YbInCu₄, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both EuNi₂(Si_0.18Ge_0.82)₂ and YbInCu₄. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRh₂Si₂. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce L₂-edge increases rapidly around 26 T corresponding to the metamagnetic transition. The XMCD spectra in CeRh₂Si₂ at high magnetic fields show only a single peak as was reported in a heavy fermion ferromagnetic compound CeRu₂Ge₂ [1].

X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) in a filled skutterudite SmOs₄Sb₁₂ were measured at Os L-edge under multiple extreme conditions, T = 2.2 K, H = 10 T, and P up to 3.5 GPa in order to obtain information of Os 5d electronic states. At ambient pressure, small dichroic signal of 0.1% was clearly observed and the orbital and spin magnetic moments of Os 5d are estimated to be -0.001 μ_B and 0.012 μ_B, respectively. At high pressure, the XMCD intensity reaches a maximum around 0.6 GPa, and decreases with increasing pressure as to finally disappear at 3.5 GPa. This trend is similar to the reported magnetization under high pressure. The behavior of Os 5d electronic states strongly connects with a novel feature observed in SmOs₄Sb₁₂.

In order to probe pressure-induced modification in Co magnetic state in Laves phase RCo₂ (R = Dy, Ho, and Er) compounds, we have measured X-ray magnetic circular dichroism (XMCD) under high pressure. The RL₂-edge XMCD indicates that Co magnetic moment M_Co gradually decreases as the pressure increases. The Co K-edge XMCD shows that the effect of R molecular field is significantly suppressed under high pressure. As a result, it is revealed that the pressure variation of M_Co is closely associated with R-Co interaction. The Co magnetic state is separately discussed from that of R partner.

The ability to combine the complementary characteristics of experimental probes is often highly advantageous for advancing our understanding of the physical and chemical properties of structurally disordered systems such as aqueous solutions. Two techniques that have been very influential in this field are neutron diffraction with isotopic substitution and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. By taking advantage of the recent significant developments in computational power and associated analytical methods, it is now possible to produce comprehensive three dimensional atomistic models of these systems that are consistent with both sets of experimental data. One such method is Empirical Potential Structure Refinement, and this study will illustrate its capabilities in an investigation of a 1:500 aqueous solution of rubidium bromide in water. Hydrogen-deuterium isotopic subsitution is used to probe the details of the structural correlations between the solvent water molecules, and Rb and Br K-edge EXAFS is used to validate the structural aspects of the incorporation of the solute ions into the bulk solvent matrix. The resulting model allows an estimate to be made of the extent of ion pairing that occurs in the dilute solution.

While theoretical standards such as those from FEFF have many advantages for EXAFS analysis, the quality of fit statistics and estimation of parameter uncertainties has always been somewhat problematic using them. Even though the calculations reproduce EXAFS features sufficiently well to give bond distances accurate to 0.01Å or so, fits to high-quality experimental spectra will have fit residuals far larger than the experimental uncertainties. One of the possible causes for this mis-fit is from approximations made in the phenomenological calculations of the inelastic losses, though this has been difficult to test conclusively in the past. Recent improvements in calculations of inelastic losses using a many-pole self-energy (MPSE) using a real-space calculation of the dielectric function have been shown to give significant improvements in XANES calculations. Here, we discuss the use of MPSE calculations for EXAFS analysis, and show that these calculations from FEFF8.5 can quantitatively improve fit quality for EXAFS, reducing mis-fits by a factor of 2 or more compared to FEFF6. This approach may also allow the semi-physical fit parameter S₀² to be avoided. The implications for improving precision for EXAFS analysis and the nature of the remaining fit residual are discussed.

Recently developed approach to the simulation of configuration-averaged EXAFS spectra using the combination of quantum mechanics and classical Molecular Dynamics (MD) methods is presented on the example of the Ti K-edge in SrTiO₃ at T = 300 K. The method allows one to significantly reduce the number of fitting parameters required in the EXAFS signal calculation and to account entirely for disorder contributions. We show also that the sensitivity of configuration-averaged EXAFS spectra to the force field model employed in the MD simulations allows one to use them as additional information for the force field parameters fitting.

A systematic EXAFS study has been performed on crystals affected by negative thermal expansion (NTE) and characterized by different structures: diamond-zincblende, cuprite, delafossite. Some general common features emerge from the results. The nearest-neighbours bond thermal expansion measured by EXAFS is always positive; within each family of isostructural compounds, the stronger is the lattice NTE, the larger is the positive bond expansion. A correlation can be established between the NTE properties and the anisotropy of relative vibrations with respect to the bond direction. EXAFS results are consistent with phenomenological models of NTE based on the competition between stretching and tension effects.

In recent work, a model for the structural environment of Hg bound to a catalytic DNA sensor was proposed on the basis of EXAFS data analysis. Although severely constrained by limited data quality and scant supporting structural data, a compelling structural model was found which agreed with a similar but less detailed model proposed on the basis on NMR data. I discuss in detail the successes and limitations of the analytical strategy that were implemented in the earlier work. I then speculate on future software requirements needed to make this and similarly complex analytical strategies more available to the wider audience of EXAFS practitioners.

EXAFS is an important experimental technique for determining the local atomic structure of nanoclusters embedded in a bulk material. In practical cases, nanocluster samples do not contain homogeneous clusters of just one size, and the average cluster size is strongly influenced by the specific distribution of cluster sizes. Combinations of different cluster sizes might provide very similar results; this issue is called polydispersity. The goal of this study is to understand if there are any principal limitations for EXAFS studies related to polydispersity. Here a new approach based on EXAFS simulations followed by linear combination (LC) on EXAFS spectra is presented. The simulations were performed on pure Cu and binary Cu-Fe clusters. The main result of this study concerns the proof that polydispersity does not affect XAFS studies on nano-clusters within a size of up to 140 atoms.

Proper application of error analysis techniques remains uncommon in most EXAFS analyses. Consequently, many researchers in the community remain distrustful of parameter-error estimates. Here, we demonstrate the accuracy of conventional methods through r-space fits to simulated data. Error estimates are determined as a function of r by averaging many scan simulations in r-space. The statistical-χ² value can then be calculated. Since ⟨χ²⟩ corresponds to the degrees of freedom in a fit, we check Stern's rule for the number of independent data points in an EXAFS spectra. Finally, we apply these simple methods to real data from a Cu foil, highlighting the overwhelming role of systematic errors in theoretical backscattering functions and pointing to the ultimate power of the EXAFS technique if such errors could be removed.

The effect of stochastic noise on Extended X-ray Absorption Fine Structure (EXAFS) data measurement, analysis, and fitting is discussed. Stochastic noise reduces the ability to uniquely fit a calculated model to measured EXAFS data. Such noise can be reduced by common methods that increase the signal-to-noise ratio; however, these methods are not always practical. Therefore, predetermined, quantitative knowledge of the level of acceptable stochastic noise when fitting for a particular model system is essential in maximizing the chances of a successful EXAFS experiment and minimizing wasted beamtime. This paper outlines a method to estimate, through simulation, the acceptable level of stochastic noise in EXAFS spectra that still allows a successful test of a proposed model compound.

We propose a new method for studying multilayer structure using angle resolved extended x-ray absorption fine structure (EXAFS) measurements. The linear integral equation describing a connection between the fluorescence intensity for spectrum of element C, the incident beam energy E, the incident angle ϕ and the concentration profile p(z,C) has been derived. It is a Fredholm integral equation of the first kind, it belongs to the class of ill-posed problems and for solution it needs special methods. We use the regularization method. For determining the depth-dependent partial interatomic distances we use angle resolved EXAFS data. The effectiveness of the method has been tested during numerical simulation on the model crystalline three-layer with BCC structure: Cr/Fe/Cr.

Multiple Scattering (MS) theory, via the MXAN package, is able to reproduce the experimental XANES data of aqua ions, small molecules, and metal sites in biomolecules from the edge up to 150–200 eV. In this paper we present the last advances of the method, including the potential description and optimization. Improved parameterization also includes new routines to handle the structural determinants via generalized degrees of freedom. Examples will be presented to illustrate the method.

The EXAFS spectra of Cu and Pd foil from many different beamlines and synchrotrons are compared to address the dependence of the amplitude reduction factor (S₀²) on beamline specific parameters. Even though S₀² is the same parameter as the EXAFS coordination number, the value for S₀² is given little attention, and is often unreported. The S₀² often differs for the same material due to beamline and sample attributes, such that no importance is given to S₀²-values within a general range of 0.7 to 1.1. EXAFS beamlines have evolved such that it should now be feasible to use standard S₀² values for all EXAFS measurements of a specific elemental environment. This would allow for the determination of the imaginary energy (Ei) to account for broadening of the EXAFS signal rather than folding these errors into an effective S₀²-value. To test this concept, we model 11 Cu-foil and 6 Pd-foil EXAFS spectra from around the world to compare the difference in S₀²- and Ei-values.

Because of the typically rather low trace element concentrations in biological samples XAS is collected in fluorescence mode with the help of a multi-element detector. In addition, several scans have to be accumulated and thus post-processing operations have to be carried out after the measurement, e.g. selecting good detector channels, checking for radiation damage, fitting of background and normalization. KEMP2 is a freely available post-processor implementing all these steps, while maintaining universal applicability by separating the instrument- and beamline-dependent steps like energy-calibration etc. from XAS-generic tasks. Thus, KEMP2 has the potential to serve as a highly automated data pipeline assisting both senior and novice users.

MAX is a new EXAFS and XANES analysis package, replacing our old "EXAFS pour le Mac" software suite. The major improvement is the ability to work with strictly the same code, compiled at once for Microsoft Windows, Apple MacOSX and LINUX systems, justifying the title "Multiplatform Applications for XAFS". It is organized as four modules: ABSORBIX (X-ray absorbance and fluorescence self-absorption calculations), CHEROKEE (EXAFS and XANES data treatment), ROUNDMIDNIGHT (EXAFS modeling and fit) and CRYSTALFFREV (from crystal structures and molecular modeling to FEFF EXAFS and XANES theoretical calculations). Most features developed in "EXAFS pour le Mac" are still available, but with much improvements in the user's interface, data treatment algorithms and new functionalities.

A Johann-type X-ray fluorescence spectrometer for XES, RXES/RIXS, HERFD XAS and RXS experiments was designed, constructed and commissioned at the X10DA-SuperXAS beamline of the Swiss Light Source. The spectrometer consists of three key elements: a sample manipulator, an X-ray dispersive element (spherically bent silicon or germanium crystal), and an one-dimensional-array X-ray detector. The detected X-ray fluorescence energy is scanned by changing the angle between the sample, crystal and detector. The energy resolution of the spectrometer ranges from sub-eV to several eV. Thanks to the use of a one-dimensional array detector the spectrometer is easy to align and operate.

Glass polycapillary optics are shown to be easy to use focusing optics for bending magnet XAS stations. These achromatic optics have acceptances of several mm horizontally and vertically, while their angular acceptances can be matched to the source divergence by the design of the polycapillary. A polycapillary half-lens based focusing system was successfully tested for transmission and fluorescence μ-XAS at the DUBBLE beamline (BM26A, ESRF) and the feasibility of confocal μ-XANES in fluorescence mode is presented.

Transmission efficiencies of 25–45% with flux density gain factors of about 2000 and beam sizes of 10–20 μm were obtained in the 7–14 keV energy range. Although the polycapillary optic has a smoothly changing energy dependent transmission efficiency, the amplitude and shape of the EXAFS oscillations are not influenced by this. The focusing properties of the polycapillary lens cancel slight vertical motions of the incoming X-ray beam, resulting in a fixed μ-beam spot in the focal plane, making polycapillaries also suitable optic in combination with a non-fixed exit monochromator.

In addition, by mounting a second polycapillary half-lens in front of an energy dispersive detector, a confocal set-up is obtained, which restricts the part of the sample seen by the detector to a microscopic volume of about 20×20×15 μm³ at the Fe K absorption edge for example.

The INE-Beamline for actinide research at the synchrotron source ANKA is operated by the Institut für Nukleare Entsorgung (INE) at the Forschungszentrum Karlsruhe. Experiments on radioactive samples with activities up to 10⁶ times the limit of exemption inside a safe and flexible double containment concept are possible. One great advantage of the beamline is its close proximity to INE's active laboratories with its equipment for manipulation of actinide materials and state-of-the-art spectroscopic, analytical, and microscopic instrumentation. This constellation is unique in Europe.

The INE-Beamline is built primarily to serve INE in-house research associated with safe disposal of high level nuclear waste such as actinide speciation or coordination-, redox-, and geo-chemistry of actinides. A wide energy range from around 2.1 keV to 25 keV covering the K-edges from P to Pd and the L3, L2, and L1 edges for actinides from Th to Cm can be used. The INE-Beamline is optimized for X-ray absorption spectroscopy techniques (XANES/EXAFS), but x-ray fluorescence (XRF) analysis and powder diffraction (XRD) are also possible, as well as surface sensitive measurements in grazing incidence geometry (GI-XAFS). Upgrades of instrumentation and extension of experimental capabilities at the INE-Beamline are driven by user needs. Two of the recent upgrades are presented: 1) installation of a microfocus option for spatially resolved studies (μ-XRF, μ-XANES, μ-XRD) and investigations of small volumes (e.g., heterogeneous natural samples and diamond anvil high pressure cells); 2) construction, and commissioning of a high resolution x-ray emission spectrometer (HRXES); 3) availability of an electrochemical cell for investigation of redox sensitive systems.

The Versatile Spectroscopy beamline at Diamond Light Source, I20, is currently under construction and aims to begin operation in late 2009 and early 2010. The beamline aims to cover applications from physics, chemistry and biology through materials, environmental and geological science. Three very distinctive modes of operation will be offered at the beamline: scanning X-ray Absorption spectroscopy (XAS), XAS in dispersive mode, and X-ray emission spectroscopy (XES). To achieve this, the beamline has been designed around two independent experimental end-stations operating from a pair of canted wigglers located in a 5m diamond straight section. One branch of the beamline will deliver monochromatic x-ray radiation of high spectral purity to one of the experimental hutches, whilst the other branch will constitute an energy dispersive spectrometer. The novel design of the beamline allows both branches to operate simultaneously.

During the past twenty years, XAS has progressed from being a technique only suitable for specialists to become a widely applicable tool. This situation has resulted from the steady development of reliable spectrometers and new generations of software for data analysis. B18 will be a general purpose XAS beamline on Diamond. It will cover a wide energy range (2 to 35 keV), with a monochromator designed to carry out both conventional and QEXAFS measurements. The main design novelty is that the low and high energy optic branches will run in parallel and the appropriate branch for a given experiment will be selected by changing the position of the slits, instead of by moving the optical elements. This will allow us to develop a very high level of automation in the operation of the instrument. Detection systems will include transmission, fluorescence and electron yield. Experience shows that considerable value is added by combining techniques. Therefore provision has been made for wide angle X-ray diffraction studies to be incorporated into the beamline architecture. The instrument will offer a variety of sample environments and the flexibility to integrate set-ups designed by the users. Hence, B18 will be able to contribute to research programs across a wide range of scientific disciplines, e.g. solid state physics and materials, catalysis, chemistry, soft matter, surfaces and biomaterials. The instrument will open to first users in April 2010.

The hard X-ray beamline BL 8 at the 1.5 GeV electron storage ring DELTA is described, and experimental data of different fields of research are presented. Making use of the intense X-ray beam emitted by a superconducting wiggler, the beamline is dedicated to X-ray absorption experiments. Three different monochromator crystal pairs are permanently available for experiments in the spectral range from about 1 keV to ca. 25 keV photon energy. Results of reference materials show that high quality EXAFS data can be obtained using Si(111) and Si(311) monochromators. First measurements in the energy range between 1.2 and 5 keV have been accomplished using YB₆₆(400) monochromator crystals. The experimental hutch accommodates a unique 6-axis diffractometer which is well suited for all kinds of diffraction and absorption experiments, including the grazing incidence geometry. The diffractometer can carry heavy loads related to non-ambient sample environments such as e.g. ultrahigh vacuum sample stages or cryostats. Here we present typical results obtained at BL8 in different areas of materials science including investigations of dilute alloys by fluorescence mode EXAFS and the study of the structural changes associated with temperature induced spin transitions of metallo-supramolecular polyelectrolyte-amphiphile-complexes.

Beamline BL01B1 was constructed for conventional XAFS measurements using a bending magnet light source at SPring-8 in 1997 [1]. BL01B1 covers a wide energy range from 3.8 to 113 keV using an adjustable inclined double-crystal monochromator and a double mirror system. Here, we describe a newly developed apparatus and the current status of the BL01B1. A time-efficient QEXAFS method was developed to measure high quality spectra up to high-k regions in the shortest possible time. The method involves sweeping the monochromator continuously at a variable angular speed depending on the k-region using a VME stepping motor controller. During scanning, a pair of crystals of the monochromator rotates without translation motion like a channel-cut crystal. This QEXAFS method was applied to the fluorescence mode using a 19-element Ge detector combined with a digital X-ray processor system. A new conversion electron yield detector having a rotational sample stage was developed for single crystalline samples. Angular oscillations of 4 degrees in the sample rotation stage around the axis normal to the sample surface successfully remove diffraction noise in the XAFS spectra.

MARS (Multi Analyses on Radioactive Samples) beamline is the hard X-ray bending magnet beamline dedicated to the study of radioactive matter of the new French synchrotron SOLEIL. The beamline, which has been built thanks to a close partnership and support by the CEA, has been designed to provide X-rays in the energy range of 3.5 keV to 35 keV. This allows to encompass M and L absorption edges of actinides, as well as K edges of transition metals (that are present in alloys and fuel claddings) up to heavy halogens, rare gases and alkalis (fission products in nuclear fuels). The MARS project aims to extend the possibilities of synchrotron based X-ray characterizations towards a wider variety of radioactive elements and a wider variety of techniques than what is currently available at other facilities. Thus, its specific and innovative infrastructure has been optimized in order to carry out analyses on materials with activities up to 18.5 GBq per sample for α and β emitters and 2 GBq for γ and n emitters. So, today, more than 70 different elements and more than 350 different isotopes have been proposed for studies on the beamline by the involved user community. The arrangement of the different elements in the optics hutch is based on an original scheme which permits to have two alternative optical configurations (monochromatic or dispersive) depending on the nature of experiments to be performed. At least three main techniques are progressively being proposed on the three complementary end-stations located in the experimental hutch: transmission and high resolution powder diffraction (TXRD and HRXRD), standard and dispersive X-ray absorption spectroscopy (XAS and EDXAS) and X-ray fluorescence (XRF). In addition, by using the KB optics, a micro-focused beam will be available on the second station of the monochromatic branch. The beamline is currently under commissioning. The first two experimental stations, using the monochromatic branch, are scheduled to be operational at the end of the year.

The optical layout of the XAFS beamline at ELETTRA is presented along with its powerful capabilities for collecting XAFS spectra in a wide energy range 2.4 – 27 keV. Recent developments around the ensemble of available instruments made available different collection modes using various sample environments. In particular combined x-ray absorption and diffraction patterns can be collected even at high temperature using a special version of the l'Aquila-Camerino furnace and a MAR image-plate detector. An automated beamline control software allows us to perform successive measurements in different conditions without attending the beamline. Examples of XAFS and diffraction measurements, as well as single-energy temperature scans are presented showing the performances of the beamline for nanocrystalline systems and liquid metals under high temperature conditions.

Laboratory EXAFS facilities have been used since long. However, EXAFS data analysis has not been reported as yet for the spectra recorded photographically. Though from our laboratory we have been reporting various studies employing X-ray spectrographs using the photographic method of registration of EXAFS spectra, but the data has never been analyzed using the Fourier transformation method and fitting with standards. This paper reports the study of copper metal EXAFS spectra at the K-edge recorded photographically employing a 400 mm curved mica crystal Cauchois type spectrograph with 0.5 kW tungsten target X-ray tube. The data obtained in digital form with the help of a microphotometer has been processed using EXAFS data analysis programs Athena and Artemis. The experimental data for copper metal foil have been fitted with the theoretical standards. The results have been compared with those obtained from another laboratory EXAFS set up employing 12 kW Rigaku rotating anode, Johansson-type spectrometer with Si(311) monochromator crystal and scintillation counter. The results have also been compared with those obtained from SSRL. The parameters obtained for the first two shells from the photographic method are comparable with those obtained from the other two methods. The present work shows that the photographic method of registering EXAFS spectra in laboratory set up using fixed target X-ray tubes can also be used for getting structural information at least for the first two coordination shells.

Under conditions of Anomalous X-ray Transmission (known as the Borrmann Effect), an X-ray standing wave is set up inside a crystal, leading to a strong reduction in electric dipole absorption. We show that electric quadrupole absorption is not similarly diminished and is thus relatively enhanced by a large factor. Absorption measurements, made under thick-crystal Laue (transmission) diffraction conditions in Gd₃Ga₅O₁₂ (GGG) and Y₃Fe₅O₁₂ (YIG), show a range of spectral features that can be assigned unambiguously to electric quadrupole events. This phenomenon, which seems to have been overlooked for decades, opens up new possibilities for studying important electronic states with hard x-ray beams. In this paper, we outline the origin of the effect and a phenomenological description of its temperature dependence, and consider the possibility of measuring the angle dependence of enhanced quadrupole absorption.

We discuss the information on the electronic structure that can be obtained by K-shell absorption and emission spectroscopy in systems that contain 3d transition metals. We remind the reader that the chemical sensitivity of the X-ray absorption near edge structure (XANES) is strongly influenced by the local geometry. The X-ray fluorescence is mostly sensitive to the electronic structure and thus complementary to XANES.

Information on valence orbitals and electronic interactions in single crystal systems can be obtained through orientation-dependent x-ray measurements, but this can be problematic for a cubic system. Polarisation-dependent x-ray absorption measurements are common, but are dominated by dipole transitions which, for a cubic system, are isotropic even though a cubic system is not. Many edges, particularly for transition metals, do have electric quadrupole features that could lead to dichroism but proximity to the dipole transition can make interpretation challenging. X-ray Raman Spectroscopy (XRS) can also be used to perform orientation-dependent near-edge measurements – not only dependent on the direction of the momentum transfer but also its magnitude, q. Previous XRS measurements on polycrystalline materials revealed that multipole (higher order than dipole) transitions are readily observable in the pre-threshold region of rare earth N_4,5 edges, actually replacing the dipole at high-q. We have extended these studies to examine orientation-dependent XRS for CeO₂ and MnO single crystals, as prototype systems for theoretical treatment. Dichroism is observed at both the Ce N_4,5 and Mn M_2,3 edges in these cubic materials.

Double-slit and forward focusing effects in XPD spectra from H₂O and GeCl₂ molecules have been theoretically studied within the single scattering approximation. In low-and intermediate-energy region, the double-slit effect can be observed. In contrast, this effect wears off and only forward focusing peaks with simple structure are given in high-energy region. The double-slit effects can be observed under special conditions where the two scattering amplitudes have finite overlap in the bisecting direction.

We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s levels of CO molecules up to a photoelectron kinetic energy (KE) of ∼150 eV. The backward-scattering intensities exhibited a strong modulation as a function of the kinetic energy of the photoelectrons, whereas the intensities for the forward-scattering gradually increased and then became nearly constant over KE ∼100 eV. Multiple scattering calculations with a muffin-tin potential qualitatively reproduced the experimental results. The present results may be considered as the observation of low-energy photoelectron diffraction patterns for gaseous free CO molecules, which are involved in modulations in extended X-ray absorption fine structure (EXAFS) spectra.

EuLγ₄ emission spectra show a large chemical shift (∼5 eV), depending on the valence state of a compound. The applicability of this emission to valence-selective X-ray absorption fine structure spectroscopy was demonstrated by performing partial fluorescence yield measurements using a 1:1 mixture of EuS and Eu₂O₃ and using valence-fluctuating compounds, such as Eu₃Pd₂₀Ge₆ and BaMgAl₁₀O₁₇:Eu.

The core excitations of the furan and carbon dioxide molecules have been studied using dispersed UV-visible fluorescence spectroscopy. Balmer-α (Balmer-β) emission was measured at the O 1s and C 1s (O 1s) excitations of furan, while emission due to an excited state of the neutral oxygen atom was measured at the O 1s excitations of CO₂. The excitation functions of the emission lines display both valence and Rydberg resonances, but the latter are more enhanced.

The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and in space. We present results on the electronically excited high-spin state structure of an Fe(II) molecular species, [Fe^II(bpy)₃]²⁺, in aqueous solution, resolving the Fe-N bond distance elongation as 0.2 Å. In addition an analysis technique using the reduced χ² goodness of fit between FEFF EXAFS simulations and the experimental transient absorption signal in energy space has been successfully tested as a function of excited state population and chemical shift, demonstrating its applicability in situations where the fractional excited state population cannot be determined through other measurements. Finally by using a novel ultrafast hard x-ray 'slicing' source the question of how the molecule relaxes after optical excitation has been successfully resolved using femtosecond XANES.

Laser pump/XAFS probe study of Ge using the high efficiency facility at PNC/XOR CAT at sector 20 of the Advanced Photon Source (APS) has discovered some surprising results of how the excited electrons/hole (e/h) decay. The 200 femtosecond (fs) pulse laser is triggered at the frequency of the APS ring so as to use the x-rays of one pulse of the 24 singlet mode at 100% efficiency. The higher efficiency of the use of the ring's x-rays (about two orders more efficient than usual) allowed the measurement of XAFS spectra at a large number of delay times between laser pump and x-ray probe and at different laser powers. The XAFS data determined the time dependence of the relative distances and their vibration amplitudes of the first and second Ge neighbors. The laser pulse excites a classical long wavelength optical mode that within 0.1 picoseconds (ps) or so excites only the vibrations of the 1st neighbor while to excite the second neighbor requires decay of the excited e/h through coupling with incoherent phonons. The surprising result is that this decay is delayed 11 ps, independent of the laser power as it is increased by a factor of two.

Describing the nature and structure of molecular excited states is important in order to understand their chemical reactivity and role as intermediates in photochemical reactions. The recent implementation of x-ray absorption spectroscopy in the ultrafast time domain allows studying the electronic and structural dynamics of photochemically active molecules in solutions. In this work we present the structural determination of a photoexcited diplatinum molecule, [Pt₂(P₂O₅H₂)₄]^4-, which plays a photocatalytic role in important chemical conversions. A novel analysis of time-resolved EXAFS spectra based on the fitting of the experimental transients obtained from optical pump/x-ray probe experiments has been performed to derive a contraction of 0.31(5) Å of the two Pt atoms and a ligand expansion of 0.010(6) Å. The former is assigned to the formation of a transient Pt-Pt bond in the excited state, while the latter indicates a concomitant weakening of the Pt-ligand coordination bonds.

Oxygen K-edge x-ray absorption spectra of water are discussed. The spectra of gas-phase water, liquid water and ice illustrate the sensitivity of oxygen K-edge x-ray absorption spectroscopy to hydrogen bonding in water. Transmission mode spectra of amorphous and crystalline ice are compared to x-ray Raman spectra of ice. The good agreement consolidates the experimental spectrum of crystalline ice and represents an incentive for theoretical calculations of the oxygen K-edge absorption spectrum of crystalline ice. Time-resolved infrared-pump and x-ray absorption probe results are finally discussed in the light of this structural interpretation.

In this paper we show how polarizable molecular dynamics can be successfully used to understand lanthanoid(III) (Ln) hydration. In particular, our modelling is in very good agreement with EXAFS data and thus the microscopic picture emerging directly from dynamics can be useful to understand experiments. We show three examples across the series: at the beginning (Nd³⁺), middle (Gd³⁺) and end (Yb³⁺). Using these examples, we show that we are able to reproduce not only Ln-oxygen distances but also the changeover in coordination number across the series. The peculiarity of the changeover of lanthanoid coordination number in the middle of the series emerges from high exchange frequency, such that a molecular dynamics approach becomes a fundamental tool to understand this phenomenon.

Structural modifications of the Zn²⁺ hydration properties under high pressure (up to 2.85 GPa) have been investigated by Molecular Dynamics (MD) simulations and the first shell structural results have been experimentally validated by X-ray Absorption spectroscopy. The first shell hydration complex of the Zn²⁺ ion retains an octahedral symmetry with a shortening of the Zn-O distance up to 0.04 Å and an increase of the thermal motion. The structural transformations occurring to water with increasing density are also investigated by MD simulations; the effect of pressure is to increase the number of interstitial water molecules, while the tetrahedral first shell cluster is only slightly distorted in the high-density conditions.

Aqueous fluids play a significant role in the transport of heat and matter in the Earth's crust and the upper mantle, and high-field-strength elements such as Zr are important geochemical tracers for these processes. However, the dissolution mechanism and complexation of Zr in the fluids at high pressure and temperature are unknown, in part because very low concentrations present severe experimental challenges. Here, we present an experimental setup for in-situ investigation of the coordination environment of elements at low concentrations in aqueous fluids up to 800 °C and 1.5 GPa using XAFS. Experiments were carried out in a modified hydrothermal diamond-anvil cell optimised for the detection of the fluorescence signal. We have investigated the effects of silicate components dissolved in aqueous fluids on the Zr solubility and complexation at high pressure and temperature. The observed Zr concentrations in fluids containing 7–33 wt% Na₂Si₂O₅ and variable Al contents were between 75 and 720 ppm at 500 to 750°C and ∼300 MPa to ∼700 MPa. Initial XAFS results show clear differences between spectra of Zr in an HCl solution and in an H₂O-Na₂Si₂O₅ aqueous fluid, implying considerable differences in the Zr complexation.

The standard model for dissolved Cu(II) portrays the complex ion as an axially elongated, equatorially planar octahedron. Using EXAFS and MXAN analyses of copper K-edge XAS spectra, new structural models for dissolved [Cu(aq)]²⁺ and [Cu(amm)]²⁺ have been determined. These structures uniformly depart from the octahedral model in favour of an axially elongated square pyramidal core. MXAN results also indicate that the equatorial ligands need not be coplanar with copper. Further structural elements include a -z axially localized scatterer at ∼3 Å. Even more distant scatterers imply second shell solvent organization, which can vary with the medium. Preliminary results from new extended, k = 18 Å^-1, higher resolution copper K-edge XAS data sets are reported. The low symmetry of dissolved Cu(II) ion contradicts the central thesis of the rack-induced bonding hypothesis of copper electron transfer proteins. The asymmetry of biological copper is not a frozen vibronic excited state enforced by a rigid protein scaffold, but is entirely in harmony with the structural ground state of the dissolved aqueous Cu(II) complex ion.

CuBr₂ solutions at different concentrations were studied by extended X-ray absorption fine structure (EXAFS) at the Cu K edge. In the saturated solution Cu²⁺ ions have chemical bonds with 3.0 oxygen atoms and 0.9 Br ion at about 1.96 Å and 2.42 Å, respectively. It indicates that the CuBr₄^-2 configuration exists with a ratio of 25% under this condition. In the dilute solutions no evidence of Br ions contributions in the first shell around Cu²⁺ ions occurs. The almost identical X-ray absorption near edge structure (XANES) and EXAFS characters address similar local environments around Cu²⁺ in agreement with results of the EXAFS fit taking into account only the contributions of Cu-O bonds.

The total-reflection X-ray spectroscopic technique was applied to an interfacial species at the liquid-liquid interface. The XAFS spectrum of bromide ions at the heptane-water interface was successfully obtained in the fluorescence mode. A slight change in the spectra was observed in the presence of the cationic surfactants, dimethyldilaurylammonium and stearyltrimethylammonium ions. This suggested that the hydrated structure of bromide ions attracted by the cationic surfactants at the heptane-water interface is different from neat interfaces or bulk aqueous phases.

We study the structure of inclusion complexes of α-, β-, γ-cyclodextrin with mono-iodide ion in aqueous solution by means of iodine K-edge EXAFS spectroscopy. The analysis is based on the assumption that two kinds of iodide ions exist in KI-cyclodextrin aqueous solution i.e. hydrated mono-iodide ions and one-one mono-iodide-cyclodextrin inclusion complexes. In KI-α-cyclodextrin system, iodine K-edge EXAFS analyse show that the average coordination number of the oxygen atoms in water molecules in the first hydration shell decreases as the fraction of included ions increases. This result suggests that dehydration process accompanies the formation of the inclusion complex. This is not found in the case of β-cyclodextrin, indicating that in this case the iodide ions are included together with the whole first hydration shell.

The analysis of the EXAFS signals from ⁷⁰Ge and ⁷⁶Ge has evidenced the low-temperature effect of isotopic mass difference on the amplitude of relative atomic vibrations. This effect is reflected in the difference of the Debye-Waller factors of the first three coordination shells, and on the difference of nearest-neighbour average interatomic distances, evaluated with femtometer accuracy. The experimental results are in agreement with theoretical expectations.

Zn_1-xBe_xSe is an interesting II-VI semiconductor showing unusual phonon behavior for 0.19<x<0.81which has been ascribed due to presence of chains of Be and Se with two slightly differing Be-Se bond distances. EXAFS data have been recorded for several compositions of Be in this mixed crystals at the Zn and Se K edges and analyzed to determine the nearest and next nearest neighbor distances for Zn and Se atoms as a function of "x". The effects of these chains is observed in the form of an increase in the σ² value of the Be-Se bond at x = 0.42 and 0.55 as compared to smaller "x" values of 0.06, 0.16 and 0.27. Theoretical estimates show that the bond length difference between the two Be-Se bonds is ∼ 0.04Å, which seems to be too small to be resolved as two different bond lengths but could be observed only as increase in σ² value for larger values of "x". The trends in the various bond angles as a function of "x" have also been explained in terms of the distorted tetrahedral structure in the ternary.

N – K edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy is applied in order to determine implantation-induced changes in the electronic structure of GaN. The samples were implanted with 700 keV In ions and fluencies in the range 5×10¹³ – 1 × 10¹⁶ ions/cm². The NEXAFS results are discussed in combination with Rutherford backscattering (RBS) characterization which assesses the implantation induced damage. The main implantation effects on the NEXAFS spectra are: (a) a fluence-dependent broadening of the NEXAFS peaks, (b) emergence of a pre-edge shoulder (RL1) that is attributed to N split-interstitials and (c) appearance of a post-edge sharp peak (RL2) that is attributed to molecular N₂ trapped in the GaN matrix. The RL2 is characterized by fine structure due to vibronic transitions that result from a change of the vibrational quantum number along with the electronic transition. The concentration of the interstitials and the N₂ molecules as well as the width of the NEXAFS peaks, have a sigmoidal dependence on the logarithm of the ion fluence, following the behaviour of the defect concentration deduced from the RBS measurements.

CdTe is affected by a low-temperature negative thermal expansion (NTE) of the lattice parameter, whose strength and temperature interval are intermediate between those of the iso-structural crystals Ge and CuCl. EXAFS measurements have been performed on CdTe from 19 to 300 K. The first-shell analysis has led to an accurate evaluation of the bond thermal expansion and of the parallel and perpendicular MSRDs. The values of the relevant parameters measured by EXAFS for CdTe are intermediate between the corresponding values previously found for Ge and CuCl.

Local order is studied in Mn-doped ternary semiconductors with chalcopyrite structure. We report the Mn K-edge X-ray absorption spectra detected by the high-energy-resolution fluorescence at the manganese Kβ emission line. The spectra are compared with the theoretical XANES calculated for different atomic sites by the real-space multiple-scattering approach and the finite difference method. The latter approach, being a non-muffin-tin method, gives a much better match to the near-edge spectra. However, no definite Mn site assignment has been reached. Spin selective examination of the pre-edge portion of the XANES indicates 3d⁵ configuration of Mn in all compounds studied. On the other hand, an effective spin derived from the Kβ emission spectra is between 2 and 2.5 due to the Mn-S bond covalency.

To understand the role of Sr in doped aluminium-silicon alloys, we have conducted for the first time, Sr- K edge XAFS measurements on Al-3%Si-0.04%Sr. Aluminium-Silicon alloys are widely used in automobile and aerospace applications. Modification of these alloys with addition of trace levels of Sr (200–400 ppm) results in changing the morphology of Si eutectic from "plate" like structure to "fibrous" structure. Several theories have been proposed to understand the mechanism of modification of eutectic phases with Sr addition in these alloys, but there is no conclusive evidence in support of these theories. From our XAFS analysis, we suggest Sr-Si bonds and Sr-Sr correlations may be responsible for the morphological transformation observed in the alloy.

Solution growth method is a suitable growth technique to obtain a large-sized and good crystalline quality β-FeSi₂ single crystal. However, during the solution growth method, solvent atoms are often automatically doped into the growing crystals and may affect properties of them. In this work, we investigated Ga atoms in β-FeSi₂ grown from a Ga solvent by EXAFS and discussed the effect of the Ga atoms on electrical properties of β-FeSi₂. The results of the EXAFS measurement indicated that 60% of Ga in β-FeSi₂ substituted Si sites, and 40% of them substituted Fe sites. The ab-initio calculation of electron density of states indicated that when the concentration of Ga in β-FeSi₂ is so high as 1.0at%, the residual Ga is not the origin of the p-type conductivity of the β-FeSi₂ crystal grown from the Ga solvent. We should conduct further calculation to decide if the residual Ga is the origin of the p-type conductivity or not in the real β-FeSi₂ crystal with only 0.1at% of Ga.

We have investigated the effect of hydrogenation on La 5d and 6p electronic states in metallic LaH_x (x = 0.0, 2.0, 2.3, and 2.6) by X-ray absorption near edge structure at the La L-edges. As the hydrogen content x increases from 0 to 2.6, white-line intensity at the La L_2,3-edges shows a remarkable increase in the range of x>2.0. This is interpreted as the increase in La 5d hole induced by interstitial H atoms on the octahedral sites. On the other hand, the shoulder structure at the La L₁-edge disappears in the process of x = 0.0rightarrow;2.0, indicating that the p-d hybridization is weakened by H atoms on the tetrahedral sites. This study demonstrates that H atoms on the two interstitial H sites provide different contribution to the modification of the electronic states.

Seven Ni-superalloy foils have been studied using EXAFS together with X-ray diffraction and electron microprobe fluorescence mapping. The usefulness of EXAFS in characterising changes during heat treatment and in differences in the host phase of minor elements has been demonstrated, in addition to the ability of multiple-scattering RMC simulations to give reliable and accurate information on local lattice distortions in these alloys.

Tribological materials from the wheel and the wheel chock of a railway train were studied. The samples were taken from new and used wheels and wheel chock. Experimental x-ray absorption near edge spectra (XANES) spectra above the Fe L2,3 edges show the variations in the shape of the Fe L 2,3 edge fine structure, that correspond to the formation of Fe oxidized layer during the process of dry friction. Elemental analysis shows the large variations of element's distribution along the surface within 10 nm depth of damaged sample.

The characteristics of K, L₁ and L₃-edges XANES spectra of group IV, V, VI compounds, which have different coordination number, number of d-electrons and the symmetry of coordination sphere, have been classified. Two p → d transitions were observed in the second derivative spectra of L₃-edge XANES spectra of all group IV, V, VI compounds. These two transitions can be assigned to split d orbitals. The splitting and area of the two resonances depend on the symmetry of coordination sphere because the splitting corresponds to ligand field splitting of d orbitals. The splitting of d orbitals has a correlation with the pre-edge peak area of K or L₁-edge XANES spectra, which are attributed to the dipole forbidden transition of s → d occurred by mixing of p orbitals with d orbitals. This correlation is supported by DFT calculations of several group IV, V, VI structural models (four-, five- and six-coordinated). The clarification of the correlation between the splitting of the resonance and the structure of group IV, V, VI metal is important to provide structural information in unknown group IV, V, VI metal site.

The resistive switching state in Cr-doped SrTiO₃ was induced by applying an electric field. This was done in ambient air and in an atmosphere of H₂/Ar. The distribution of the thereby introduced oxygen vacancies was studied by spatially resolved X-ray fluorescence images. It was concluded that the oxygen vacancies were introduced in the interface between the SrTiO₃ and the positively biased electrode.

In order to elucidate the hydrogen effect on the atomic configuration in the Ni-Nb-Zr glassy alloys, we measured Ni, Nb, and Zr K-edge XAFS spectra of the Ni-Nb-Zr glassy alloy films with two different chemical compositions, i.e., Ni₄₂Nb₂₈Zr₃₀ and Ni₃₆Nb₂₄Zr₄₀, and their hydrogen-charged ones, i.e., (Ni₄₂Nb₂₈Zr₃₀)_0.91H_0.09 and (Ni₃₆Nb₂₄Zr₄₀)_0.89H_0.11. The Fourier transforms of the XAFS oscillations of these samples clearly shows that there is a significant difference in the structural response between the Zr30at.% and the Zr40at.% alloys when hydrogen atoms are charged. The curve-fitting analysis indicates that the hydrogenation does not alter the local alignment around the three metal atoms for the Zr30at.% alloy, but for the Zr40at.% alloy; it elongates the inter-atomic distances of Zr-Zr, Zr-Nb and Nb-Ni. On the basis of the curve fitting analysis, we propose the distorted icosahedral Zr₅Ni₅Nb₃ cluster models. The XANES spectra at each (Ni, Zr and Nb) edge of (Ni₃₆Nb₂₄Zr₄₀)_0.89H_0.11 also present the distinct shape from the other samples. The pre-edge peak (shoulder) vanishes or weakens, suggesting the conversion of the electronic state of the metal ions owing to the hydrogenation. The post-edge energy region shows clear multi-scattering effects from hydrogen atoms by charging these.

Neutron diffraction and Extended X-ray Absorption Fine Structure (EXAFS) studies have been carried out on a range of praseodymium gallate glasses (Pr₂O₃-Ga₂O₃) prepared by aerodynamic levitation and laser heating. The short and intermediate range ordering around the rare-earth have been obtained by a multi-technique method. The results show that simple molecular dynamics simulations give a good representation of the coordination structure around the rare-earth in these glasses.

Lanthanum barium gallate proton conductors are based on disconnected GaO₄ groups. The insertion of hydroxyls in the LaBaGaO₄ network proceeds through self-doping with Ba²⁺, consequent O^2- vacancy formation to fulfill charge neutrality. With a structural investigation on self-doped LaBaGaO₄ oxides using synchrotron XRD and EXAFS on the Ga K-edge, we find that: (a) the GaO₄ tetrahedra retain their size throughout the whole series; (b) the GaO₄ tetrahedra rotate as rigid bodies on hydration, leading to the formation of a network of shorter O-O configurations that are stabilized by hydrogen bonds; (c) contraction of the lattice occurs along the a unit cell axis, as a consequence of an overall structural rearrangement of the hydrated solid.

Europium-doped calcium tungstate (CaWO₄:Eu) was synthesized by a modified Pechini method. X-ray absorption near-edge structure (XANES) and X-ray excited optical luminescence (XEOL) was employed to probe the chemical and luminescence properties of CaWO₄:Eu. XANES results demonstrate that the chemical environment around calcium in the doped CaWO₄ is similar to that of undoped CaWO₄. On the other hand, chemical environment around oxygen is very different. Moreover, the results suggest that contributions to luminescence in the sample are from both silica (from silica matrix) and CaWO₄. Using XEOL, luminescence pathways and efficiency associated with the system can be identified.

Sulfur is an important element of glasses, not because of its amount, always very low (less than 0.4 % in weight of SO₃), but because of its role since it actively participates to the refinement process and, combined to other elements, it can be responsible for the coloration of the glass. Iron is also of a major importance in most of the glasses. In the case of the float glass, the two faces, because of the fabrication process, are different in terms of composition (presence of Sn for one face) and also in terms of oxidation state of these minority elements (Fe, Sn, S). There should be a subttle interplay between the concentrations and the oxidation states of these different minority elements, and anyway these variations occur over a thickness of the order of few micrometers below the surface.

Using the high intensity and the focusing properties (3 × 3 μm²) of the x-ray beam from the Lucia beamline, we have therefore studied the speciation of iron and sulfur near the face of a float glass in relation with the behavior of tin. This has been obtained by combining elemental x-ray fluorescence cartography and x-ray micro-absorption at the different K-edges.

Temperature dependent Re L₃-edge EXAFS signals from perovskite-type cubic ReO₃ have been successfully interpreted using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering approach. The force field model, required for MD simulations, has been determined by fitting the Re-O and O-O pairwise interatomic potentials to a set of experimental data (lattice parameter, elastic constants and bulk modulus) and phonon frequencies, theoretically calculated from the first principles at high symmetry points of the Brillouin zone. The MD simulations reproduce well the anisotropy of thermal vibration for oxygen atoms and confirm a deviation of the mean Re-O-Re angle from 180°. The atomic configurations from the MD simulations have been used to calculate the configuration-averaged EXAFS spectra at several temperatures. The use of the MD results allows a straightforward treatment of thermal disorder in the multiple-scattering contributions to the total EXAFS signal. Good agreement between calculated and experimental EXAFS signals has been found, that additionally supports the accuracy of our force field model.

The structure of PbZr_0.40Ti_0.60O₃ crystalline ferroelectric material was studied by powder X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) at Ti K-edge and Extended X-ray Absorption Fine Structure (EXAFS) at Pb L_III-edge. The XRD Rietveld refinement shows a tetragonal crystal structure. The resulting crystal model was used to calculate both theoretical XAFS spectra. The mismatch beween experimental and calculated XAFS spectra is interpreted as a consequence of the random distribution of Ti and Zr. The resulting disorder effect is averaged in the long-range structure probed by XRD whereas the XAFS techniques probe the local order of each site.

La-doped barium titanate (Ba_1-xLa_xTiO₃) is an important electronic ceramic material used in a wide variety of applications including in multilayer capacitor, transducers, ferroelectric thin film memories, and positive temperature coefficient resistor (PTCR). In this work, we investigated the changes of the local atomic structure around barium and titanium ions of Ba_1-xLa_xTiO₃ compounds prepared by solid state reaction using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The X-ray Absorption Near-Edge Structure (XANES) spectra at the Ti K-edge (4966 eV) and Ba L_III-edge (5247 eV) were analyzed. Our findings suggest that La³⁺ doping can modify the degree of covalency of the Ti-O bonds, but cause no change in the BaTiO₃ unit cell volume and the atomic coordinate around Ti⁴⁺, Ba²⁺ions.

The UV irradiation effect in the practical luminescence material (Pr, Al)-doped SrTiO₃ was investigated by x-ray absorption spectroscopy at the Ti K-edge. Two characteristic peaks observed in difference spectra between UV off- and on-spectra show different UV energy dependence; above the common onset UV energy of ∼3.3 eV, which is nearly equal to the band-gap energy, a difference peak at the main absorption edge changes its intensity in accordance with the photoluminescence excitation spectrum, while another difference peak in the pre-edge region does not. Through the consideration of the energy scheme, the Ti 3d conduction-band bottom is responsible for the pre-edge features and is rather insensitive to UV energy, whereas the main edge together with other features in the higher-energy region is attributable to the upper-lying 4p states that are strongly influenced by UV light via valence holes. These results enable us to propose a mechanism of UV absorption followed by visible light emission.

XAFS at the copper K-edge has been recorded for cuprous oxide and cupric oxide separately and also for a mixture of the two in a specific ratio, at the XAFS beam line at SSRL. The normalized μ(E) data obtained for the two oxides, i.e., Cu(I) and Cu(II) oxides separately was linearly combined to fit the normalized μ(E) data of the mixture using the Linear Combination Fitting (LCF) method. The values obtained for the statistical goodness-of-fit parameters, R-factor and chi-square, show that the fit is reasonably good. This procedure yielded the percentage of the oxides in the mixture which was found to be nearly the same as the actual percentage which was used to prepare the mixture. Another method based on the analysis of normalized difference absorption edge spectra has also been used to quantitatively determine the percentage of the two copper species in the mixture. The LCF method is, however, found to be better than the normalized difference absorption edge analysis.

The structural, magnetic and electronic properties of transition metal oxides reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray scattering (RXS) allows us to perform an accurate investigation of all these electronic degrees. RXS combines high-Q resolution x-ray diffraction with the properties of the resonance providing information similar to that obtained by atomic spectroscopy (element selectivity and a large enhancement of scattering amplitude for this particular element and sensitivity to the symmetry of the electronic levels through the multipole electric transitions). Since electronic states are coupled to the local symmetry, RXS reveals the occurrence of symmetry breaking effects such as lattice distortions, onset of electronic orbital ordering or ordering of electronic charge distributions. We shall discuss the strength of RXS at the K absorption edge of 3d transition-metal oxides by describing various applications in the observation of local anisotropy and charge disproportionation. Examples of these resonant effects are (I) charge ordering transitions in manganites, Fe₃O₄ and ferrites and (II) forbidden reflections and anisotropy in Mn³⁺ perovskites, spinel ferrites and cobalt oxides. In all the studied cases, the electronic (charge and/or anisotropy) orderings are determined by the structural distortions.

The emergence of superlattice periodicities at metal to insulator transitions in hole doped perovskite oxides responds to a rearrangement of the local atomic structure, and electron and spin density distribution. Originally, the ionic model based on a checkerboard- type atomic distribution served to describe the low temperature charge and orbital ordered (COO) phases arising in half- doped manganites. In the last years, the exploitation of resonant x- ray scattering (RXS) capabilities has shown the need to revisit these concepts and improve the picture. Yet, we have realised that COO is a more common phenomenon than expected that can be observed in a wide range of doping levels. Here we compare the experimental data recently collected by RXS on La_0.4Sr_1.6MnO₄ (x=0.60) and La(Pr)_1/3Sr_2/3FeO₃ (x=0.67). The first shows a COO phase similar to that found in the x=0.5 sample but angular peak positions vs. T denotes the incommensurability of superlattice reflections. Meanwhile, the analysis of the commensurate CO phase in the studied ferrite underlines the role of the structural changes also involving La(Sr) and O atoms.

We here report a combined experimental and theoretical resonant x-ray scattering study in two isomorphous compounds, LaMnO₃ and TbMnO₃. The two samples show an orthorhombic Pbnm structure with four Mn³⁺ atoms at equivalent positions. The Mn sites have a local inversion symmetry and they are surrounded by nearly tetragonal-distorted oxygen octahedron. The tetragonal distortion is larger in TbMnO₃ than in LaMnO₃. Resonances were measured at the Mn K-edge of the (h,0,0), (0,k,0) and (0,0,1) (h,k,1=3,5) reflections. All the reflections show a resonance only in the σ-π' polarization channel. The observed resonant intensities exhibit a sin²ϕ dependence on the azimuth angle ϕ. The (h,0,0) and (0,k,0) reflections have identical energy dependence but markedly different than the (0,0,1) reflections. Differences in the energy line shape and width of these resonant reflections between La and Tb samples are explained in terms of the different tetragonal distortion and the different ionic radius of the rare-earth. The origin of the two types of reflections (related to two different nonzero non-diagonal elements of the scattering tensor) is explained within the multiple scattering theory considering long-range order of structural distortions in a cluster up to 63 atoms without invoking any d-orbital order.

We report here soft resonant x-ray scattering (SRXS) measurements on a single crystal of highly stoichiometric Fe₃O₄ (Verwey transition at T_v = 123.5 K). Resonant intensity was observed at the Fe L_2,3 and the O K edges for the (0,0,1/2) reflection and at the Fe L₁-edge for the (001) reflection in the low temperature phase. The energy, azimuthal angle and temperature dependence was explored using either σ- or π-incidence. The (001) reflection is active in the σ-σ' polarization channel whereas the (0,0,1/2) reflection is in the σ-π' polarization one. The (0,0,1) reflection is also observed at energies below the Fe L₁-edge, confirming that this reflection is permitted by the crystal symmetry of the low temperature phase. On the other hand, the (0,0,1/2) reflection is strictly forbidden and scattered intensity is only observed on resonance. The resonant and non-resonant signals simultaneously disappear at T_V for the two studied reflections at both the Fe L-edges and the O K-edge. This result indicates that the resonant reflections and the associated electronic anisotropy of the Fe d, Fe p and O p-states are explained by the lattice distortions.

The pressure dependence of the x-ray magnetic circular dichroism (XMCD) has been measured in spinel ferrites (Fe₃O₄ and CoFe₂O₄). Room temperature XMCD spectra have been collected at the Fe K-edge measuring the difference in absorption between two helicity states of the photon. We measured from ambient pressure up to almost 23 GPa in the case of Fe₃O₄ and to 27 GPa in case of CoFe₂O₄. The XMCD spectra of Fe₃O₄ decrease monotonically as the pressure increases being the dichroic signal at 23 GPa half of that observed at ambient pressure. On the other hand, the dichroic signal almost disappears at 27 GPa in CoFe₂O₄. This result evidences a pressure-induced phase transition from a ferromagnetic state to a nonmagnetic state. We note that the two signals, one from the tetrahedral and the other from the octahedral Fe atoms, disappear simultaneously indicating a strong reduction of the ferromagnetic order of the two sub-lattices. In addition to this phenomenology, a clear variation of the XANES spectra at the same pressure indicates that this transition comes from a structural change. Moreover, when releasing the pressure, the dichroic signal is not recovered, even in new measurements at ambient pressure.

At room temperature, magnetite (cubic inverse spinel structure, Fd-3m s.g.) shows metal-like electrical conductivity, which discontinuously drops by two orders of magnitude below ca. 120 K (T_v). This is due to a first-order phase transition, where the cubic structure is distorted to monoclinic symmetry (Cc s.g.). Models for this metal-insulator transition are still highly debated. We performed 1s3p as well 1s2p RIXS measurements well below and above T_v on a sample of synthetic magnetite powder to probe any difference present in the electronic states. Neither 1s3p nor 1s2p RIXS spectra reveal any differences between the two phases. Our observations are consistent with earlier EXAFS data and indicate no changes in the local structural geometry around Fe.

Local crystalline structure of hypo- and hyperstoichiometric SmCo_x alloys with x = 5.15, 4.95, 4.0, 3.75 heat treated in different conditions was investigated by means of the X-ray absorption spectroscopy. Experimental spectra were measured above the L₃-Sm absorption edge. EXAFS-analysis shows that stacking faults appear in hyperstoichiometric alloys SmCo₄ and SmCo_3.75, confirming the hypothesis of "high coercive state, induced by phase transformations, changing the state of the grain surface in basic phase". L₃-Sm XANES spectra demonstrate the reduction of the "white line" amplitude in Sm-enriched samples.

We show that K-edge X-ray absorption spectroscopy can be used as a sensitive probe of electron correlations in V₂O₃. This is possible thanks to a detailed study of the V K pre-edge region while changing the thermodynamic parameters of the system. LDA+DMFT provides an interpretation of the changes in the electronic structure, in particular in the upper Hubbard band, at the Mott transition. The possibility of modifying the Coulomb interaction and observing the metal-insulator transition by applying an external pressure is also demonstrated, which is of particular interest for the study of many strongly correlated materials.

X-ray absorption spectra of the oxide systems Nd_2-xCe_xCuO_4-δ (NCCO) above the K-Cu absorption edge were investigated in temperature range 4 ÷ 300 K. It is assumed that oxygen ions in superconductive CuO₂ plane move in a double-well potential similarly to abnormal oxygen vibrations uncovered earlier in superconductive systems Ba_1-xK_xBiO₃ and La_2-xSr_xCuO₄. A model of relationship between electronic and local crystalline structures is proposed. Obtained results point to the direct connection of the observed local dynamic structure nonuniformity with local dynamic charge ordering. Role of dynamic charge ordering in superconductive CuO₂ plane in HTSC mechanism is discussed.

Carrier-induced lattice distortion (signature of strong electron-lattice interaction) in oxypnictide superconductors is found by a local structural study using extended x-ray absorption fine structure (EXAFS). Local lattice instability (polaron formation) is detected as an anomalous upturn of the mean-square relative displacement for the nearest neighbor distances (Fe-As) in LaFeAsO_1-xF_x (x = 0.07), implying a local lattice distortion that develops below 70 K and disappears at the superconducting critical temperature. Comparing the results with the lattice response in cuprate superconductors, intimate correlation between local lattice mode and superconductivity is revealed. The results suggest that strong electron-lattice interaction is present as a common ingredient in the microscopic mechanism of s uperconducting transition.

The local structure of the double perovskite (Sr_2-xCa_x)FeMoO₆ (0 ≤ x ≤ 2.0) and Sr₂CrMO₆ (M = Mo, W) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe and Cr K-edges. It was found that the Fe-O distance decreases from 1.999(7) Å (x = 0) to 1.991(1) Å (x = 1.0) in (Sr_2-xCa_x)FeMoO₆ with a tetragonal phase (I4/m). When the x value is further increased from 1.5 to 2.0, the Fe-O bond distance decreases from 2.034(5) to 2.012(4) Å with a monoclinic phase (P2_1/n). On the other hand, Cr-O, Cr-Sr and Cr-W bond distances in Sr₂CrWO₆ are all slightly longer than the corresponding bond distances in Sr₂CrMoO₆, which is attributable to the larger ionic radius of W⁵⁺ (0.62 Å) than Mo⁵⁺ (0.61 Å).

The present study aims, by using X-ray Absorption Spectroscopy, to describe the local process towards the pressure-induced abrupt changes in the resistivity in the Jahn-Teller distorted LaMnO₃ doped compounds. Local environment of manganese atoms under pressure up to 37 GPa has been studied by X-ray absorption spectroscopy. We identify successive steps towards the pressure-induced abrupt changes in the resistivity. These steps are associated to local processes such as the opening of the inter-octahedra tilt angles and the average symmetrization of the Mn local environment. All modifications present a hysteretic behavior when the pressure is released, pointing to the coexistence of MnO₆ distorted and undistorted units.

We investigate the local structural change under antiferro- and ferromagnetic transition for annealed Fe_50.4Rh_49.6 alloy. Both Fe and Rh K-edge EXAFS are analysed up to second nearest neighbours. For first nearest neighbour Fe-Rh (or Rh-Fe), the temperature dependence of the interatomic distance and Debye-Waller factor is well understandable and reproduced by other structural techniques. On the other hand, that for the second nearest Fe-Fe is quite mysterious; the interatomic distance is longer than the value deduced from the corresponding change of the first nearest Fe-Rh but the Debye-Waller factor for Fe-Fe decreases as temperature under the transition. In ferromagnetic phase, the coherent motion of Fe atoms is expected to be prominent. We propose the model that the transition progresses by three steps with temperature, T₁, T₂, and T₃.

The filled skutterudites RT₄X₁₂ (R: rare-earth, T: transition metal, X: pnictogen) show a variety of intriguing features by changing the combination of R, T, and X. Among them, some compounds shows characteristic feature called "rattling" that is considered as anharmonic oscillation or off-centered motion of rare-earth ions accommodated in the icosahedron cages made from pnictogen and "rattling" is suggested to contribute to the various features of this system. We applied extended X-ray absorption fine structure (EXAFS) on this system to clarify the microscopic mechanism of "rattling" motion [1]. Temperature dependence of EXAFS thermal (Debye-Waller) factors of R-Sb and T-Sb atomic pairs were analyzed by Einstein model. Thermal oscillation and static distortion are analyzed independently. From this study, we could know systematic information about "rattling" as a large amplitude oscillation of rare-earth ions and static distortion that has two types of cage space dependence.

Recent calculations by Maiti et al. have shown that non-magnetic ions like Sr/Ca in Sr/Ca ruthenates may not be mere spectators in the magnetic transitions but their strong hybridization with O atoms may modify the magnetic ground state by distorting the Ru-O-Ru bond angle. Our XAFS results at Sr and Ru K-edges on SrRuO₃ indeed demonstrate that the Debye Waller factor for the Sr-coupled bonds viz. Sr-Sr evolve most significantly across the ferromagnetic transition, almost replicating the magnetization curve while the Ru-octahedra evolves only gradually. This clearly establishes the definite role of Sr disorder in the ferromagnetic transition.

X-ray absorption fine structure (XAFS) and first-principles calculations are effectively combined to establish correlations of fabrications, atomic and electronic structures as well as ferromagnetism for the Mn-doped dilute magnetic semiconductors (DMS), and to shed light on the magnetism origin for a variety of ZnO-, GaN-, and Si-based DMSs. The results of Mn:ZnO and (Mn,N):ZnO thin films reveal that either the existence of Zn vacancy or N substitution of O sites can stabilize the ferromagnetic interactions between neighboring Mn-Mn pairs, and enhance the magnetic moment per Mn. In a 2.5at.% Mn-doped GaN film, a part of substantial Mn ions is found to locate at the interstitial sites near the substitutional Mn ions, forming Mn-Mn dimers that possess unique electronic and magnetic properties. Similar phenomena have also been found in the Mn-doped Si system in which the interstitial Mn atoms intend to assemble together via an intervening substitutional Mn ion. We have proposed a pathway to understand the microscopic origin of ferromagnetism in the DMS materials from the viewpoint of experimental determination and theoretical calculations.

Dilute magnetic semiconductors combine both magnetic ordering and semiconducting behaviour, leading to potential spintronic applications. Silicon containing dilute Mn impurities is a potential dilute magnetic semiconductor. We have grown Mn delta-doped films by deposition of 0.7 of a monolayer of Mn on Si(001) by molecular beam epitaxy and capping the film with Si. The magnetic properties are likely sensitive to the distribution of Mn on substitutional or interstitial sites and the formation of metallic precipitates. We have used polarization-dependent XAFS to examine the local structure. We compare to a thicker MnSi film grown on Si(111) and also examine the influence of lead on the manganese environment when used as a surfactant in the growth process.

The X-ray absorption spectra around the Cr K-edge are observed to reveal the strange behaviour on the magnetism of the dilute magnetic semiconductor GaCrN with a cubic structure (F3 m = Td²). The radial distribution function analyzed in the part of the X-ray absorption fine structure shows the splitting in the first and the second nearest neighbours into two peaks, indicating that the Cr ion substitutes the Ga ion but shifts from just the lattice site of the Ga ion. This local lattice instability breaking the symmetry is explained by pseudo-Jahn – Teller effect. In the relation to the local lattice instability, the electronic ground state of the Cr ion in the cubic GaN is discussed.

Geometric structures for II-VI diluted magnetic semiconductor iodine-doped Zn_1-xCr_xTe films (x = 0.05) grown by molecular-beam epitaxy with high-temperature ferromagnetism were investigated by using fluorescence x-ray absorption fine structure (XAFS) measurement in order to elucidate the relationship between the geometric structure and the magnetic properties. The XAFS analysis has revealed that the local structures around Cr atoms are dependent on the growth temperature. For the samples grown at 360 and 390 °C, the majority of Cr atoms are tetrahedrally coordinated to Te atoms, indicating the formation of substitutional Cr on Zn-site in ZnTe lattice and/or zinc-blende (ZB) CrTe. On the contrary, for the samples grown at 300 and 330 °C the additional formation of secondary phases such as Cr-Te compounds was suggested. Therefore, it is deduced that the formation of secondary phase such as Cr-Te compounds are related to the increase of Curie temperature. The XAFS analysis has also revealed that the local structures do not depend on the I concentration. For the samples with different I concentrations, the Cr atoms form substitutional Cr on Zn-site in ZnTe lattice and/or ZB CrTe, corresponding to the result of TEM measurement.

Fluorescence X-ray absorption fine structure (XAFS) technique was used to investigate the local structures of the doped Mn in the Mn_xGe_1-x dilute magnetic semiconductors (DMSs) with different Mn content (x=0.07, 0.25, 0.36) prepared by magnetron cosputtering method. The results indicate that for the sample with low Mn content (x=0.07), the Mn atoms are mainly incorporated into the lattice of Ge, and locate at the substitutional sites of Ge atoms with the ratio of 75%. With the Mn content increasing to 0.25 or higher, only part of Mn atoms enter the lattice of Ge and the others exist in the form of the Mn₅Ge₃ phase whose content increases with the doped Mn concentration. It is found that, in the Mn_0.07Ge_0.93 the bond length of the first (Mn-Ge) shell is R_Mn-Ge = 2.50 Å, which is bigger than the first (Ge-Ge) shell distance in Ge by about 0.05 Å. These results imply that local structure expansion is induced by dilute Mn substituting into Ge sites.

The local structure of the doped Mn in the Mn_xSi_1-x dilute magnetic semiconductors (DMSs) fabricated by magnetron cosputtering method are studied by fluorescence X-ray absorption fine structure (XAFS) at Mn K-edge. It is found that the occupation of Mn atoms in the Mn_xSi_1-x DMS strongly depends on the Mn content. The Mn K-edge XAFS results indicate that for the sample with low Mn content (x = 0.03∼0.08), the Mn atoms are incorporated into the lattice of Si, and substitute part of the Si sites. As the Mn content reaches 0.15, Mn atoms mainly form the phase of Mn₁Si₁ compound.

X-ray absorption near-edge structure (XANES) spectroscopy was used to investigate the local structures of Fe_0.05Si_0.95 diluted magnetic semiconductors (DMSs) thin film deposited by radio-frequency (RF) reactive magnetron co-sputtering device at temperatures of room-temperature (RT), 473K and 573K. Using the ab inito self-consistent real-space multiple-scattering approach, the experimental XANES spectra can be well reproduced by the theoretical calculation curves. The results indicate that the majority of Fe atoms are located at Si substitutional sites Fe_Si in Fe_0.05Si_0.95 at the room temperature. Upon increasing the temperature to 473 and 573 K, the majority of Fe atoms tend to form the FeSi₂ compound.

The x-ray absorption near-edge structure (XANES) and first-principles calculations were employed to study the local structure and magnetic origin of Co-doped rutile TiO₂ thin film. It is found that the experimental Co K-edge XANES can be reproduced by the calculated spectrum of substitutional Co (Co_Ti) with O vacancy (V_O), suggesting the coexistence of Co_Ti and V_O in this system. First-principles total energy calculations further reveal that the O vacancy prefers to reside near the Co ion and substantially facilitates the impurity doping. The electronic structure analysis indicates that the O vacancy can mediate the ferromagnetic interaction between the Co_Ti ions and thus is responsible for the observed room-temperature ferromagnetism in the Co-doped TiO_2-δ thin films.

Recent progresses in the depth-resolved X-ray magnetic circular dichroism (XMCD) and X-ray absorption fine structure (XAFS) techniques are presented. The depth-resolved atomic and magnetic structures of Co films grown on Ru(0001) was investigated by using the depth-resolved XMCD and extended X-ray absorption fine structure EXAFS. The three-dimensional magnetic structure of a micro-patterned Fe/Ni/Cu(100) film was studied by combining the depth-resolved XMCD with the X-ray microbeam. The technique was also applied to Co thin films covered with a relatively thick Mo overlayer, in order to demonstrate the possibility to investigate ex-situ samples with a protection layer.

Effects of NO adsorption on the magnetism of Fe(2 and 4 ML)/Cu(001) films have been studied. XMCD spectra have been measured for the films before and after NO adsorption. The bare 4 ML Fe film is magnetized perpendicularly, and m_s^eff is 2.5 μ_B. However, the NO adsorbed 4 ML Fe film exhibits in-plane magnetization and shows m_s^eff of 1.2 μ_B, which is about a half of m_s^eff of the bare film. The apparent fifty percent reduction of m_s^eff can be attributed to an idea that m_s^eff of 1 ML aligns in the opposite direction to that of the other 3 MLs'. This antiferromagnetic coupling between the topmost layer and the other layers is suggested by the careful analyses of the depth resolved XMCD spectra.

An analytical approach to the analysis of ReflEXAFS data collected from complex multilayer samples, at a range of angles above and below the critical angle is presented. The aim of the technique is to generate a structural model of the investigated system that is consistent with the variable depth sensitivity of the experimental data. The procedure follows three main steps (i) the determination of the free atom reflectivity background for the multilayer system, (ii) the estimation of the depth dependent EXAFS signals and (iii) the calculation of the corresponding ReflEXAFS components. By iterating between steps (ii) and (iii), and varying the estimates of the EXAFS signals, a consistent set of structural parameters is extracted that reflects the bulk structure of the multilayer system through the basic reflectivity signals, and the depth dependent local atomic structure through the estimated EXAFS components. An example of the depth dependent structure of copper in a copper-chromium multilayer stack is presented to illustrate the capabilities of the method.

In order to investigate the electronic and magnetic structures of each atomic layer at subsurface, we have proposed a new method, Auger electron diffraction spectroscopy, which is the combination of x-ray absorption spectroscopy (XAS) and Auger electron diffraction (AED) techniques. We have measured a series of Ni LMM AED patterns of the Ni film grown on Cu(001) surface for various thicknesses. Then we deduced a set of atomic-layer-specific AED patterns in a numerical way. Furthermore, we developed an algorithm to disentangle XANES spectra from different atomic layers using these atomic-layer-specific AED patterns. Surface and subsurface core level shift were determined for each atomic layer.

X-ray absorption spectroscopy (XAS) has been used to clarify the thickness-dependent magnetic properties in nanometric CoPt films. We get benefit from the variation of the sampling depth with the grazing angle to investigate the variations of the local order within the film. In order to properly resconstruct the 3D information the experiments were performed either in the in-plane as in the out-of-plane geometries and supported by ab initio calculations. A depth dependence in the chemical order is revealed and the magnetic behavior is interpreted within this framework.

The spin-reorientation transition of thin Au/Co/Au films, grown in-situ on W(110), is studied in XMCD and EXAFS experiments. At 300 K, for in-situ grown Co on a Au(111) film, the dominant easy magnetization direction was found to be in the surface plane, for the uncapped Co/Au bilayers. This is a novel observation, in terms of easy magnetization direction for low thickness Co on Au. After capping with Au, a sizeable out-of-plane magnetization is observed below a thickness of four atomic Co layers. When the spin-reorientation transition occurs because of Au capping, a 5 Å thin Co layer undergoes structural changes of lattice parameters Δa/a = −1.2 % and Δc/c = +6.6 %. The observation of structural changes which accompany the spin reorientation transition, contradicts previous work on Co/Au(111), and allows to quantify the magnetoelastic energy contribution, connected with the presence of the Co/Au interface.

Reflection mode grazing incidence X-ray absorption spectroscopy at the Bi L₃-edge and simultaneous electrical resistivity measurements were used to investigate the microstructure of quench condensed thin Bi metal films on float-glass substrates at temperatures from 20 K to 300 K. While thin films of ≈ 6 nm thickness appear to be amorphous after deposition at 20 K, thicker films of about 18 nm show the well-known rhombohedral structure of bulk Bi. During a subsequent heat treatment, the amorphous structure of the thin films transforms irreversibly into the crystalline form for temperatures at (42 ± 2) K. This crystallisation is accompanied by an irreversible increase of the film resistivity by a factor of more than 2.7. The film density and roughness do not change within detection limits during the heat treatment.

[Fe (t^Fe) / Si₃N₄ (3 nm)] multilayers were prepared by sequential magnetron sputtering. The Fe layer thickness has been varied for every sample. Magnetic properties show a gradual evolution from a ferromagnetic state for samples with larger metal thickness to a granular behaviour for the samples with the smallest Fe layer thickness. Microstructural features such as average thickness and granularity, as well as the local order around Fe atoms, were studied by x-ray reflectometry and x-ray absorption spectroscopy, respectively. X-ray reflectometry suggests that the formation of discontinuous metal-insulator multilayers is produced at t^Fe ≤ 1.3 nm. Extended x-ray absorption fine structure (EXAFS) analysis shows a reduction, of the Fe-Fe coordination shell as the metal layer thickness decreases. Moreover, a new phase emerges, and it is visible at the samples with t^Fe ≤ 1.3 nm. This coordination shell is attributed to the formation of Fe-N bonds likely placed at the interface regions. X-ray absorption near edge spectroscopy (XANES) at the Fe K-edge shows as well the evolution from the metallic spectrum to a combined contribution of 2 phases as the metal layer thickness decreases. XANES calculations performed within the real-space multiple-scattering formalism of two nanometric phases for metal bcc Fe and tetrahedral FeN in zinc-blende structure provide a successful explanation of the XANES spectral evolution. The appearance of a new phase linked to the interface regions obtained by X-ray absorption analysis suggests the granular morphology of samples with t^Fe ≤ 1.3 nm.

Geometric structures for HfSiON/SiON/Si films annealed at various N₂ gas partial pressures were investigated using fluorescence XAFS measurement at Hf L_III- and L_I-edge. The XAFS analysis has revealed that the local structures around the Hf atoms strongly depend on the N₂ gas partial pressure. For the sample annealed at the N₂ gas partial pressure of 10 Torr HfN and HfSiON coexist, and for the samples annealed at the N₂ gas partial pressure above 100 Torr Hf atoms form HfSiON only. These results indicate that the formation of HfN for HfSiON/SiON/Si films can be suppressed by annealing at proper partial pressure of N₂ gas.

Polarization dependent iodine K-edge XANES spectra of iodine-doped polyvinyl alcohol (PVA) films provide much information on the local structure around iodine anion. The present multiple scattering analyses support that the iodide anions are along to the PVA chain in the films. The difference XANES spectra taken between 0° and 90° and between 45° and 90° are slightly sensitive to the local structure of the PVA film around iodine anions.

The influence of structural and compositional changes within FePt nanoparticles on their magnetic properties was studied by means of x-ray absorption spectroscopy in the near-edge regime and its associated magnetic circular dichroism as well as by analysis of the extended x-ray absorption fine structure. The magnetic moments at the Fe sites were found to be a sensitive monitor to changes of the local surrounding: While compositional inhomogeneities in the nanoparticles yield significantly reduced magnetic moments (by 20–30%) with respect to the corresponding bulk material, thermally induced changes in the crystal structure yields strongly enhanced orbital contributions (up to 9% of the spin magnetic moment). Also the break of crystal symmetry at the surface leads to an enhanced orbital magnetism which was confirmed by determination of the ratio of orbital-to-spin magnetic moment for FePt particles with different sizes between 3 and 6 nm in diameter.

XAFS measurements near the Zr K-edge for the P2₁/c and Pbca ZrO₂ phases with particle size of 62 nm and 0.50 μm were performed under pressure up to 7.8 GPa using a multi-anvil high-pressure device and synchrotron radiation at BL14B1, SPring-8, Hyogo. XANES spectra change gradually near the phase transition region of 3.0–4.8 and 4.8–7.8 for bulk and nano particles. The second-nearest Zr-Zr distance in nano particle is 0.02 Å longer than that in bulk particle. It was found that the nano particle is more compressible comparing with the bulk particle and transforms to the Pbca phase at certain specific Zr-O and Zr-Zr distances. The magnitudes of σ2 for Zr-Zr distance in the nano particle are significantly larger because of the static disorder near the surface.

An in-situ EXAFS method is developed to study the nucleation and growth processes of nanocrystals by using a microfluidic reactor which converts the time-dependent kinetics to position-dependence. As an example, we measured the Se K-edge EXAFS spectra for CdSe nanocrystals along a microfluidic reactor channel and indicated strong time-dependence of the nucleation and growth at the beginning of the reaction. A rapid increase of the reaction yield within several seconds was observed. It is found that after injection of starting materials, the nucleation occurs abruptly and the CdSe nuclei concentration reaches the maximum and then declines rapidly.

A series of Au/Al₂O₃ catalysts prepared by the different procedures and series of model system Au/Si(100), Au/Si(111) differing in the mean Au particle sizes (from 2 nm up to 30 nm) were studied by EXAFS and XANES techniques. No visible changes in electron states of Au for all samples prepared by different methods in comparison with bulk material were detected. Oxygen atoms were not detected around Au atoms within the detection limits of our study (a few per cents of surrounding atoms). A gradual reduction of the Au-Au bond length and first shell Au-Au coordination number and an increase in the Debye-Waller factor are observed as the size of supported Au particles decreases. The significant increase of structural disorder for the smallest Au particles comparatively to the bulk Au metal and sizeable particles was detected. These variations in micro-structural parameters of Au nanoparticles are in line with an increase in their catalytic activity in CO oxidation. For model systems some coordination of Au- atoms from islands and Si- atoms from crystal surface was detected for thin Au "films".

Materials showing negative thermal expansion (NTE) coefficient over large temperature ranges are nowadays of great interest for their possible applications. Small nanoparticles show changes in their properties with respect to the corresponding bulk, mainly due to the high surface to volume ratio and to the confinement of electrons in a small volume. In the present paper we report a x-ray absorption fine structure (XAFS) study on the thermal expansion coefficient of an Au foil and of Au nanoparticles of very small dimensions ranging from 2.4 nm and 5.0 nm. Their L₃ edge has been investigated in the temperature range 20K – 300K and a very accurate data analysis has been performed taking into account the presence of asymmetry effects. All clusters showed a thermal trend of the first shell distance significantly different from that of the bulk. The larger clusters were characterized by a reduction of the thermal expansion coefficient with respect to bulk; in the smallest samples the crossover from a thermal expansion to a NTE effect was observed. A simple model, based on the contribution of localized states induced by the finite size of the clusters, qualitatively accounts for the observed behaviour.

Ag nanoparticles of 1.5 to 7 nm size were produced by ion exchange of soda-lime glass for various duration. Information on local order and thermal vibrations were available by means of X-ray absorption spectroscopy using experiments at the Ag K-edge (25.514 keV). Ratio method and EXAFS fitting procedure were successfully applied to reveal the temperature dependence using the cumulant-expansion method up to third order ones. The temperature dependence of the nearest neighbor Ag-Ag distance appears different from that of polycrystalline Ag foil below 400 K. This effect can be explained by a thermoelastic model describing the mismatch of thermal expansion coefficients of Ag particles and the glass matrix. In addition, the parameter of Ag-Ag bond length of 1.5 nm particles is governed by precursor formation for crystalline Ag nanoparticles. The data of the second cumulant, the Debye-Waller factor (DWF), represent a higher static disorder, especially for nanoparticles of 1.5 – 3.5 nm size, caused by the increasing portion of surface or interface atoms. From the temperature dependent part of DWF we estimated a slightly increased Einstein temperature.

Metal nanoparticles embedded in glass have been thoroughly studied because of their specific optical properties. The present work is directed to the fabrication of bimetallic Ag/Au nanoparticles by double ion implantation and their structural investigation. Ion-implanted samples were measured at the Ag K- and Au L₃-edge at HASYLAB/Hamburg and ESRF/Grenoble, respectively, in fluorescence mode (at 10 and 20 K). The Fourier transformed spectra show Ag-Ag and Ag-O bonds for small ion doses. For high ion doses two different correlations (Ag-Ag and Ag-Au) can be found between 2 and 3 Å. At the Au L₃-edge, the high-dose implantation creates an additional Au-Ag correlation visible in the Fourier transformed spectra. These results indicate the formation of Ag-Au alloy nanoparticles for high-dose sequential implantation of Ag and Au ions (4×10¹⁶ ions/cm² in each case) whereas for lower doses mainly the ionic state of implanted ions should exist. Transmission electron microscopy characterization revealed the formation of smaller homogeneous particles of ≈5 nm mean size and larger ones of ≈15 nm that exhibit an internal void, i.e. hollow core-shell particles. EXAFS data prove bimetallic structures for all nanoparticles.

The achievement of high information density and fast recording rate in memory devices crucially depends on the structure of magnetic domains. In this paper cobalt nanoparticles are synthesised using two capping agents (TOA, ODA) and two different preparation routes: thermal decomposition (TD) and Solvated Metal Atom Dispersion (SMAD). The interaction of capping agents with free metal clusters and their influence on Co nanoparticles size, atomic structure and oxidation state is investigated by means of X-ray diffraction and X-ray absorption spectroscopy.

The Debye-Waller factors obtained by EXAFS analysis of the Te nanoparticles are analyzed by a Einstein model. The Einstein temperatures for the intra- and interchain interactions are depend on the size of the Te nanoparticles. With decreasing the size of the Te nanoparticles the Einstein temperature for the intrachain correlations increases, while that for the interchain correlations decreases. The value of the static components of the Debye-Waller factors for both the intra- and interchain correlations increase with decreasing of the size. The reduction of the interchain interactions for the Te nanoparticles would induce the increase of the Einstein temperature for the intrachain correlations and the decrease of the interchain correlations.

The local 3D structures of electrochemically deposited Cu nanoclusters on p-GaAs(100) with various coverages have been investigated by in-situ surface-sensitive x-ray absorption fine structure (XAFS) analysis. The experimental Cu K-edge XANES of Cu nanoclusters deposited on GaAs surface have been analyzed on the basis of full potential calculations of XANES in the combination with DFT geometry optimization. It has been shown that small partially oxidized Cu nanoclusters are formed when the surface coverage of the Cu overlayer is less than 0.25 monolayer. At higher coverage the Cu microclusters have a fcc structure and are almost not oxidized.

This work describes EXAFS (extended X-ray absorption fine structure), XANES (X-ray absorption near edge structure) investigation into inclusion compounds of Cu(II) complexes: Cu(acac)₂; [Cu(en)₂(H₂O)₂]²⁺; [Cu(cyclam)]²⁺ in macrocyclic cavitand cucurbit[8]uril at different stages of preparation and heat treatment in hydrogen atmosphere. The structure and composition of the nearest environment of copper atoms have been characterized; the interatomic distances and coordination numbers have been determined.

In this paper, we show that combining Multiwavelength Anomalous Diffraction (MAD) and Diffraction Anomalous Fine Structure (DAFS) spectroscopy, in grazing incidence geometry, allows to obtain structural properties (strain and composition) of semiconductor nanostructures. We report results obtained on dome-shaped Ge nano-islands grown on Si(001) surfaces and AlGaN nanowires grown on Si(100). It is shown that, in the case of sharp interfaces, MAD alone can not determine the mean Ge content in the region of the substrate-island interface and needs to be combined with Extented-DAFS measurements.

We report a synchrotron study of GeO₂ nanowires (NWs) prepared by a vapor- liquid-solid (VLS) method on a silica glass substrate. The electronic and local structure of GeO₂ NWs were studied by X-ray Absorption Near-Edge Structure (XANES) at the O K- and Ge L_3,2-edges. X-ray Excited Optical Luminescence (energy and time resolved) were used to monitor the optical emission upon X-ray absorption with the excitation energy tuned across absorption edges of interest. Using this method one obtains site specific insight into the chemical origin of luminescence.

We investigate the microstructure of Ge/Si and GaN/AlN sandwiches containing vertically aligned QDs. The study establishes an influence of blocking layers (Si, AlN) thickness, number of QDs layers (Ge, GaN) in heterostructure and annealing temperature on the microstructure characteristics of systems with quantum dots.

We examined to establish the simple synthesis method of Ag triangular nanoplates in order to elucidate their growth process. Ethanol solution of AgNO₃ was photoirradiated without reduction agents except in the presence of PVP, poly(vinil-pyrrolidone). Electron microscope observations revealed that the shape of the product was Ag triangular nanoplates with sharp corners and a flat face. In situ XAFS and optical absorption measurements suggested that the Ag triangular nanoplates were photoinduced-converted from Ag spherical nanoparticles via Ag truncated triangular nanoplates.

We have studied X-ray absorption fine structures (XAFS) of Pt nanoparticles (PtNPs) which were deposited on silicon nanowires (SiNWs). SiNWs were fabricated via an electroless chemical etching method and served as the template for the immobilization of PtNPs. PtNPs electrolessly reduced from their ionic solution by HF-treated SiNWs were found to deposit on the tips of the SiNWs. The electronic structures of Pt were studied using X-ray absorption near-edge structures (XANES) at Pt L_3,2-edge. For comparison, we also examined the Pt L_3,2-edge and the Au L₃-edge XANES of Pt-Au bimetallic nanoparticles co-deposited on SiNWs. We found that the PtNPs showed slightly increased whiteline intensity compared to that of Pt foil. When Au was deposited together with Pt, the resonance peaks of the NPs were slightly, but systematically shifted due to the formation of Pt-Au alloy.

X-ray absorption near-edge structures (XANES) at Si and C K-edge as well as X-ray excited optical luminescence (XEOL) have been used to investigate the electronic structures and optical properties of SiC microcrystals (SiCmcs) and SiC nanowires (SiCnws). SiCnws synthesized via thermal evaporation, have a SiC (β-phase)-core-SiO₂-shell morphology. We found that the XANES for SiCmcs, a 6H-SiC (α-phase) structure, shows reasonable agreement with density functional theory (DFT) calculations. As for SiCnws, we observed both SiO₂ and SiC features at the Si K-edge. It is interesting to note that upon X-ray excitation, SiCmcs emit bright light at the wavelength of 600 nm (2.07 eV), although bulk α-SiC has an indirect band-gap of 3.02 eV. SiCnws, on the other hand, exhibit luminescence at 460 nm with a shoulder at 600 nm. The analysis of these data and its implications are presented.

The paper presents the results of investigation of the chemical bond formation in fluorinated single-walled carbon nanotubes using X-ray absorption spectroscopy. All measurements were performed with the use of synchrotron radiation at the BESSY II. The C1s and F1s absorption spectra point to formation of covalent chemical bonding between the fluorine and carbon atoms in F-SWCNTs. The investigation of the local structure of the F-SWCNTs has been done on the basis of calculations by the Density Function Theory and Finite Difference methods.

AlN ferromagnetic nanorods with 5 at.% of copper were studied by using x-ray absorption spectroscopy (XAFS) above the Cu K- and L3- edges. Theoretical simulations of XAFS spectra clearly identify a formation of small copper clusters inside AlN lattice. Average size of clusters was estimated to be 50–70 atoms from the analysis of both XANES (X-ray Absorption Near Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure) regions of spectra. Calculations of magnetic moments for different types of point copper defects in AlN lattice were made.

The atomic structure models of Zn-porphyrin/C₇₀ multilayer for solar cells were examined. The local atomic structure of the Zn-porphyrin/C₇₀ complex was refined with the use of previously published results [1]. Since near-edge spectral region (XANES) is sensitive to the three-dimensional atomic geometry, the theoretical analysis of the experimental XANES was performed on the basis of finite difference method (FDMnes 2008 program code). Some electronic properties of the complex were obtained from the DFT calculations performed by means of Amsterdam Density Functional program package.

Investigation on local atomic structure of ZnO:Mn nanorods, thin films and nanoscale core/shell structures ZnO nanorods/ZnO:Mn film (10% Mn concentration) has been performed. The structures are synthesized with high pressure pulsed-laser deposition (PLD) method. Synthesis and growth of the studied structures have been considered in detail for the determination of Mn embeddings and impurities in ZnO host lattice. Theoretical analysis of experimental data have been carried out using a self-consistent real space multiple scattering method (FEFF8.4 code) and a finite difference method (FDMNES2008 code). Local structure parameters have been refined using multidimensional interpolation approach on the basis of fitting XANES spectra (Fitit2.0 code). The samples synthesized under certain condition may contain both Mn embeddings and secondary phases. It is found that the most probable model of the Mn embeddings is the structure where Mn atoms substitute for Zn atoms but a part of Mn atoms is located in interstitial sites in ZnO host lattice.

Fe₆₀Co₄₀ alloys were fabricated by the mechanical alloying process with the periods of 1, 2, 4, 6, 12 and 24 hours, respectively. The structural variations during the formation of the alloy were examined by the X-ray diffraction and the extended X-ray absorption fine structure. The activation for structural transform begins in 6 hour milling. Substantial structural changes were observed in 12 hour milling. The alloying process was almost completed in 24 hours. EXAFS analysis showed that BCC shells appeared in the alloy milled for 6 hours. The magnetization increased as milling time increased.

Organometallic complexes hosted inside porous frameworks are particularly interesting because of possible application in heterogeneous catalysis or electronic devices and optical materials. We present here a detailed spectroscopic investigation on the structure and reactivity towards simple reagents (such as CO) of chromocene molecules (Cp₂Cr) encapsulated into the nanovoids of two different matrices: a non polar polystyrene (PS) and a polar NaY zeolite. We demonstrate that stable Cp₂Cr(CO) complexes are formed in PS, while in NaY the presence of high internal electric fields confers to the Cp₂Cr molecules a much higher reactivity towards CO. In situ EXAFS data, combined with other spectroscopic techniques and ab initio theoretical calculations, allowed the structural determination of the reaction products and afforded the full comprehension of the complex reactivity of Cp₂Cr molecules inside the cavities of PS and NaY hosts.

We used EXAFS and DFT calculations to investigate the structure of [Ru(bpy)(AP)₄]²⁺ and [Ru(bpy)₂(AP)₂]²⁺ (bpy=2-2'-bipyridyne, AP=4-aminopyridyne) in aqueous solution (10 mM). These derivatives are of potential interest since, upon direct irradiation, they can form reactive aqua-species able to bind to macromolecules. An attempt has been made to determine with EXAFS the structure of the photodissociation product of the [Ru(bpy)₂(AP)₂]²⁺ complex, where a water molecule fill the coordination vacancy left by an AP ligand resulting in [Ru(bpy)₂(AP)(H₂O)]²⁺. Unfortunately, co-presence in the experimental sample of both original and photodissociated complexes, causes the failure of the analysis. This failure was due to the structural complexity of both systems and to the similarity in their EXAFS signals. This work underlines the potentialities and the limits of EXAFS spectroscopy when dealing with highly diluted samples where the local environment of the adsorbing atom is characterized by structured ligands: the local environment of Ru is correctly reproduced when dealing with homogeneous samples, while the co-presence of two or more different species makes the data analysis highly critical.

Advanced X-ray spectroscopy experiments can contribute to elucidation of the mechanism of water oxidation in biological (tetra-manganese complex of Photosystem II) and artificial systems. Although the electronic structure of the catalytic metal site is of high interest, it is experimentally not easily accessible. Therefore, we and other researchers are working towards a comprehensive approach involving a combination of methods, namely (1) quantitative analysis of X-ray absorption near-edge structure (XANES) spectra collected at the K-edge and, in the long run, at the L-edge of manganese; (2) high-resolution X-ray emission spectroscopy (XES) of Kα and Kβ lines, (3) two-dimensional resonant inelastic X-ray scattering (RIXS) spectra. Collection of these spectroscopic data sets requires state-of-the-art synchrotron radiation facilities as well as experimental strategies to minimize the radiation-induced modifications of the samples. Data analysis requires the use and development of appropriate theoretical tools. Here, we present exemplary data collected for three multi-nuclear synthetic Mn complexes with the Mn ions in the oxidation states II, III, and IV, and for Mn^VII of the permanganate ion. Emission spectra are calculated for the Mn^VII ion using both multiple-scattering (MS) approach and time-dependent density functional theory (TDDFT).

3d transition metal ions, like Fe(II) in a planar organic environment are subject to the details of the ligand coordination. In this study the 3d orbital splitting in planar D_4h symmetry is investigated for Fe(II) using the charge transfer multiplet program. By variation of the 10Dq, Ds and Dt crystal field parameters, the 3d orbitals split differently giving rise to different spin multiplicity. The relative occupations of the 3d orbitals yield a range of ground states. Experimental x-ray absorption spectra of FePc powder are compared with theoretical simulations, resulting in the spin ground state of the Fe(II) ion being ³E.

Acid sulfate soils (ASS) are soils and soft sediments in which sulfuric acid may be produced from iron sulfides or have been produced leaving iron oxyhydroxysulfates in amounts that have a long lasting effect on soil characteristics. If soil material is exposed to rotting vegetation or other reducing material, the Fe-oxyhydroxysulfates can be bacterially reduced to sulfides including disulfides (pyrite and marcasite), and Monosulfidic Black Ooze (MBO) a poorly characterised material known to be a mixture of iron sulfides (especially mackinawite) and organic matter. The chemistry of these environments is strongly affected by Fe and S cycling processes and herein we have sought to identify key differences in environments that occur as a function of Fe and S concentration. In addition to our chemical results, we have found that the effects of particle size on self absorption in natural sediments play an important role in the spectroscopic identification of the relative proportions of different species present.

In the present paper Full Multiple Scattering (FMS) theory has been applied to analyse the cobalt hexacyanoferrate XANES spectra. The use of the MXAN program has permitted to calculate the edge spectra and to perform a fitting procedure with the experimental data, obtaining a set of structural parameters. A previously reported EXAFS analysis (which includes terms up to four-body MS calculations) was performed via the GNXAS package, by a Multiple Edge approach of both Fe/Co K-edges and Fe/Co/Ni K-edges, and using the same structural parameters for all edges. The XANES data of Fe and Co K-edges are independently analysed here. An excellent reproduction of the XANES spectra, and a good agreement with the previous EXAFS results is obtained. The CN bond length using EXAFS has been determined with a statistical error of few thousandths of Å, whereas structural parameter using MXAN are probed within a 0.01–0.03 Å accuracy.

X-ray Absorption Spectroscopy (XAS) has been used to probe the local structure of copper(I) complexes containing scorpionate ligands. The EXAFS analysis, performed by using the GNXAS package, has permitted the identification of the local environment of the copper site. Copper is found to be 4-fold coordinated with two sets of Cu-N and Cu-P interactions describing a quasi planar figure, in the case of {Cu[(C₆H₅)₂PCH₂CH₂P(C₆H₅)₂][H₂B(tz^NO2)₂]}. An additional coordination is revealed for the copper complex of bis(1,2,4-triazol-1-yl)acetate due to the interaction of the copper with the acetate of the scorpionate ligand. XANES spectra behaviour confirms the occurrence of copper in the +1 oxidation state.

The oxidation of sulfur in marine archaeological timbers under museum storage conditions is a recently identified problem, particularly for major artefacts such as historic ships excavated from the seabed. Recent work on the Vasa has stressed the role of iron in catalysing the oxidative degradation of the wood cellulose and the polyethylene glycols used to restore mechanical integrity to the timbers. In developing new treatment protocols for the long term preservation of Henry VIII of England's flagship, the Mary Rose, we are investigating the potential of chelating agents to neutralise and remove the iron products from the ships timbers. We have explored the use of aqueous solutions of chelating agents of calcium phytate, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ammonium citrate to extract the iron compounds. All of these solutions exhibit some level of iron removal; however the key is to find the most effective concentration at pH of around 7 of the reagent solution, to minimise the treatment time and find the most cost-effective treatment for the whole of the Mary Rose hull. Fe K-edge XAFS data from samples of Mary Rose timbers, before and after treatment by the chelating agents mentioned has been collected. The data collected provide valuable insights into the effectiveness of the treatment solutions.

The chelate Co(2,2'-Bipy)(i-Bu₂PS₂)₂ has been studied by X-ray absorption near-edge structure (XANES) spectroscopy. The experimental Co K-edge XANES of the Co(2,2'-Bipy)(i-Bu₂PS₂)₂ has been recorded. Theoretical analysis of Co K-XANES has been performed on the basis of the full-potential finite difference method using FDMNES code and real-space self-consistent full multiple-scattering approach within the muffin-tin approximation for potential shape (FEFF8.4 program). The comparison of the theoretical spectra with the experimental data has been done and a agreement between the theoretical and experimental XANES has been obtained.

Distinct site- and state-selective dissociation following the O1s core-excitation has been found in the gaseous molecules of methyl trifluoroacetate (MTFA). The site- and state-selective dissociation was examined by measuring the branching ratios of dominant CH₃⁺ and CHO⁺ fragments. The branching ratios from MTFA showed that site-selective dissociation takes place via the excitation from the different atomic sites to the same π^*_CO resonance state, (O1s_CO^-1π^*_CO) and (O1s_OMe^-1π^*_CO). A pronounced O1s_OMe site-selectivity was identified by a significant increment of CHO⁺ formation at the (O1s_OMe→π^*_CO) band. The site-selectivity was also justified by an equivalent core approximation using the density functional theory calculation. State-selective dissociation was identified among the (O1s_OMe^-1π^*_CO), (O1s_OMe^-1σ^*_O-Me) and (O1s_OMe^-1σ^*_C-OMe) transitions originated from the same OMe core. State-selective production of CH₃⁺ could be found at the (O1s_OMe→σ^*_O-Me) band, whereas state-selective formation of CHO⁺ was observed at the (O1s_OMe→π^*_CO) and (O1s_OMe→σ^*_C-OMe) bands.

Squalene has been used as a model compound for the investigation of sulphur crosslink in the vulcanization process. The effects of the accelerator on the crosslink were deduced from the sulfur K-edge absorption spectra. The majority of the crosslinks for the squalene vulcanized with ZDEC or TMTD is likely disulfidic, while that vulcanized with CBS or MBTS is monosulfidic.

Structure-performance relationships gained by studying catalysts at work are considered the key to further development of catalysts underlined here by a brief overview on our research in this area. The partial oxidation of methane to hydrogen and carbon monoxide over Pt- and Rh-based catalysts and the total combustion of hydrocarbons demonstrate the importance of structural identification of catalysts in its working state and the measurement of the catalytic performance at the same time. Moreover, proper cell design is a key both here and in liquid phase reactions including preparation or high pressure reactions. In several cases structural changes during preparation, activation and reaction occur on a subminute scale or the catalyst structure varies inside a reactor as a result of temperature or concentration gradients. This, additionally, requires time and spatial resolution. Examples from time-resolved QEXAFS studies during the partial oxidation of methane over Pt- and Rh-based catalysts demonstrate some of the recent developments of the technique (use not only of Si(111) but also Si(311) crystals, angular encoder, full EXAFS spectra at subsecond recording time, and modulation excitation spectroscopy). In order to obtain spectroscopic information on the oxidation state inside a microreactor, scanning and full field X-ray microscopy with X-ray absorption spectroscopic contrast were achieved under reaction conditions. If a microbeam is applied, fast scanning techniques like QEXAFS are required. In this way, even X-ray absorption spectroscopic tomographic images of a slice of a microreactor were obtained. The studies were recently extended to spatiotemporal studies that give important insight into the dynamics of the catalyst structure in a spatial manner with subsecond time-resolution.

In situ x-ray absorption spectroscopy identified partially oxidized platinum as the active phase for generating high activity during carbon monoxide oxidation over Pt/Al₂O₃. CO covers and poisons metallic platinum, which results in a low catalytic activity. The conversion in CO abruptly increased during ignition, switching from low activity to high activity, accompanied by oxidation as observed in the increased intensity of the XANES. EXAFS analysis indicated breaking of Pt-Pt bonds and the appearance of a Pt-O scatterer. The partially oxidized catalyst had a lower oxygen coordination number and shorter Pt-O bond length than bulk PtO₂, suggesting that a strongly defected platinum oxide was formed with a coordination possibly lower than octahedral. From infrared data, ignition was accompanied by the abrupt disappearance of CO adsorbed on metallic particles. The reverse changes happen with the sudden decrease in CO conversion during extinction: partially oxidized catalyst becomes reduced and covered with CO.

In the present study the structure of copper catalysts on alumina support were investigated in situ and time resolved during reduction and re-oxidation at different temperatures with the quick-scanning EXAFS (QEXAFS) technique. Different impregnation times (2 min and 90 min) were chosen for the preparation which resulted in different copper species that show a strong variation in the reduction/re-oxidation behaviour. These dynamic changes as well as possible intermediate phases during the gas atmospheres changes were followed with up to 20 EXAFS spectra per second at the copper K-edge covering an energy range of 450 eV. The high time resolution provided new insights into the dynamics of the catalysts e.g. revealing Cu(I) as intermediate state during re-oxidation. Latest advances in the data acquisition hardware are leading to an improved data quality of spectra collected at the SuperXAS beamline. Thus, not only accurate analysis of the catalysts via XANES but also by EXAFS was possible. This is also due to the recent upgrade to monitor the Bragg angle directly with an encoder during the experiments.

The local structure of Pd metal fine particles on LaFeO₃ which has a high catalytic activity was observed by dispersive XAFS optics from the viewpoint of dynamical structure change of Pd during oxide-metal change and CO/NO catalytic reaction. The oxide-metal change of Pd nanoparticles on LaFeO₃ and Al₂O₃ was investigated by 20–50 Hz rate. It was recognized that, under the reductive atmosphere, Pd atoms show similar speed of movement from oxide to metal state both on the two supports. However, under the oxidative atmosphere, Pd atoms on LaFeO₃ show faster movement from metal to oxide state than those on Al₂O₃. CO/NO catalytic reaction on Pd metal nanoparticles was also observed by 0.2 Hz rate. Slow observation mode made the four EXAFS parameters: coordination number, interatomic distance, Debye-Waller factor and edge shift, precisely determined during catalytic reaction. There are two particular differences between Pd particles on LaFeO₃ and Al₂O₃. Large enhancement of interatomic distance of Pd particle was only observed on Al₂O₃. Stable surface oxide layer of Pd particle is created on LaFeO₃.

We prepared several samples of carbon-nanotube-supported Pt nanoparticles that are potentially promising electrocatalysts for hydrogen fuel cells. Commercially obtained single-walled carbon nanotubes (SWNTs) were characterized by Raman Spectroscopy, SEM, TEM, EDS, and XANES. This multi-technique characterization allowed us to quantify the size and composition of metal impurities (Mo, Co) in SWNTs, to choose the best method to remove them, and characterize the effectiveness of their removal. After synthesizing a "nanopaper" (10–20 micrometer thick, free standing sheets of self-assembled SWNTs) we decorated it with Pt nanoparticles by electroless deposition. Formation of Pt nanoparticles was verified by EXAFS, and quantitative information about their size and structure was obtained.

A computer-controlled continuous tubular flow reactor system has been commissioned that permits time-resolved in situ XAFS measurements of organometallic reactions. The system was commissioned by Zn K-edge measurements of products formed during the Soai reaction. XANES data are shown that illustrate the quality of the data that can be achieved. The XANES spectra are compatible with the presence of dimer, trimer or other oligomeric alkoxide species in the Soai process. It is shown how heterogeneity in the Soai reaction system leads to considerable complications with the measurements due to the formation of floating particles of the aldehyde/iPr₂Zn adduct formed in the reaction; additionally, decomposition of iPr₂Zn with residual air and moisture leads to deposits on cell walls.

Platinum-nickel alloys have been considered one of the promising alternative catalysts for replacement of Pt since they show higher reactivity with less usage of Pt. To elucidate the role of Ni in the various stages of the oxygen reduction reaction and the corresponding changes to Pt in comparison with pure Pt clusters, we have conducted Pt L₃ and Ni K edge in situ XAFS measurements on carbon supported Pt and PtNi(1:1) nanoparticle catalysts under a wide range of operating potentials. We observe that in PtNi alloys the Pt-Pt bond distance is shorter and the distribution of Pt and Ni is non-uniform: Pt has a tendency to be found on the surface while Ni is mostly in the interior of the catalyst nanoparticles. In addition, while a change in oxidation of the pure Pt nanoparticles is clearly observed at different potentials, the Pt in the PtNi alloy remains nearly oxygen-free at all potentials but an accompanying oxidation change of Ni has been observed instead. This phenomenon suggests that the presence of Ni in the nanoparticle inhibits the coverage of oxygen adsorbate on Pt surface, resulting in more active sites on the Pt surface.

Supported Ni₂P catalysts are efficient for the hydrodesulfurization (HDS) of liquid fuels. In situ extended x-ray absorption fine-structure (EXAFS) analysis of the Ni₂P catalyst under realistic HDS conditions revealed the formation of Ni-S bonds in the catalyst system. In order to identify the origin of these bonds, a quick x-ray absorption fine structure (QXAFS) system was set up, which enabled measurement of one Ni K-edge EXAFS spectrum in 10 sec. In addition, a Fourier transform infrared (FTIR) unit was incorporated to the QXAFS system, which allowed simultaneous measurements of XAFS and IR spectra on the same sample. The catalyst (12.2 wt% Ni₂P/MCM-41) was activated under H₂ at 723 K to regenerate an active phosphide phase. After activation, a reaction gas mixture (thiophene/He/H₂ = 0.1/1.9/98, at a total flow rate of 102 ml/min) was introduced. Under the reaction conditions, there was a change in the pre-edge area of XANES, which corresponded to the evolution of Ni-S bonds in EXAFS. The simultaneous measurements of XANES and IR revealed that this Ni-S could be attributed to the formation of a Ni phosphosulfide species rather than bonding between Ni and S of adsorbed thiophene. The combined in situ techniques proved to be an effective tool for the characterization of working catalysts.

The structure of supported platinum catalyst (2 wt% Pt/Al₂O₃) has been determined during the sudden change in the activity of the catalyst, referred as "ignition", during oxidation of carbon monoxide. The catalyst was prepared by incipient wetness impregnation method. The active phase of the catalyst is shown to be a highly disordered platinum oxide. This surface oxide increases with the increase of carbon monoxide conversion during the ignition process, which further increased the conversion, making the process autocatalytic. The QEXAFS spectra collected at Pt L₃ edge with a time resolution of 0.5 sec are compared with the standard EXAFS that are generally collected in transmission mode and are shown to be useful to extract valuable information about the changing structure of the catalyst during the ignition.

The structure of palladium during the total combustion of methane has been studied by a combination of the complementary in situ techniques X-ray absorption spectroscopy, Raman spectroscopy and X-ray diffraction. The study demonstrates that finely dispersed and oxidized palladium is most active for the oxidation of methane. Upon heating in the reaction mixture a sudden reduction accompanied by strong sintering of the palladium particles occurs leading to a less active catalyst. Raman spectroscopy combined with XAS shows that palladium is re-oxidized during cooling but is not as finely dispersed as in its prepared state.

In-situ Scanning X-ray Transmission Microscopy (STXM) allows the measurement of the soft X-ray absorption spectra with 10 to 30 nm spatial resolution under realistic reaction conditions. We show that STXM-XAS in combination with a micromachined nanoreactor can image a catalytic system under relevant reaction conditions, and provide detailed information on the morphology and composition of the catalyst material. The nanometer resolution combined with powerful chemical speciation by XAS and the ability to image materials under realistic conditions opens up new opportunities to study many chemical processes.

Catalytic partial oxidation (CPO) of methane to hydrogen and carbon monoxide over Pt-Rh/Al₂O₃ and Pt/Al₂O₃ was studied in-situ with a new QEXAFS setup. The structural changes of the catalysts were investigated on the subsecond timescale during two reaction steps by recording both XANES and full EXAFS spectra: (1) heating and ignition in 6%CH₄/3%O₂/He, (2) periodic changes between the reaction gas mixture and H₂ atmosphere. The results showed that the ignition occurred at lower temperatures for Pt-Rh/Al₂O₃ while it was completed in a significant shorter time interval for Pt/Al₂O₃. Some structural changes during the heating phase were detectable before the reaction ignited, especially for Pt/Al₂O₃, as reflected by the performed principle component analysis. However, a closer analysis of the FT-QEXAFS data did not evidence a defined intermediate. In addition, the composition of the gas atmosphere was altered between hydrogen and the reaction mixture, enabling modulation excitation spectroscopy. This technique was for the first time applied to QEXAFS data and resulted in significantly enhanced data quality.

We investigated the change in structures during reduction and oxidation of a new type of Pd on Sr-Fe-O catalyst for exhaust emission. In situ DXAFS techniques have shown changes in palladium states and oxygen concentration simultaneously during reduction and oxidation reactions. Quantitative analysis has shown that palladium atoms change their states between Pd(II^*) and Pd(0) reversibly according to the gas atmosphere accompanying changes in the oxygen concentration. This reaction explains the high performance of the catalyst.

The stability of the Pt/KL catalyst can be greatly enhanced by the presence of the rare earth Ce. The analysis of the X-ray absorption edges indicates that some electronic differences may indeed exist in the state of Pt supported on the Ce-KL compared to that on the unpromoted KL zeolite. Although the Pt particle size and location inside the zeolite is very similar in the two zeolites, the presence of the Ce seems to have influence on the electronic potential around Pt, which may be responsible for the observed enhanced stabilization of the small metal clusters. The presence of Ce in the zeolite also greatly affects the reducibility of Pt.

The millisecond time resolution achieved by Energy Dispersive EXAFS (EDE) and the high stability provided by the unmoved optical components make this technique very attractive to study chemical reactions and elucidate reactive intermediate species. Great progress has been made on the EDE study of the problematic in situ experiments of reactions in solution. Herein, limitations and solutions for the study of these systems are given. Two examples of catalytic reactions followed in situ and carried out in a stopped-flow/UV-Vis spectroscopy/EDE set-up are shown.

Nanocrystalline Ru_1-xNi_xO₂ materials were synthesized by a solution method. Local structure around doped Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS) functions obtained from X-ray absorption spectra acquired at Ni-K edge (8333eV). It was found that Ni ions are confined to the Ru site in the RuO₂ rutile-type crystal structure, and Ni atoms tend to group by entering neighbouring sites along the body diagonal of rutile lattice. Such a neighbourhood of two Ni atoms may act as an active site for oxygen evolution by promoting simultaneous two electron transfer from the absorbed molecule of water. The refined Ni-O bond distances suggest that oxidation state of Ni ions is between +2 and +3.

A major enterprise for scientists worldwide is the search for alternative fuels and molecular hydrogen (H₂) is a promising candidate. Its large-scale technical production needs to involve water-oxidation catalysts from inexpensive and abundant materials. Here, a water-oxidizing Co-based catalyst film (CoCF) is investigated. We review and extend our previous X-ray absorption spectroscopy (XAS) measurements (at Helmholtz-Zentrum Berlin/BESSY) by comparison to LiCoO₂, a Co^III compound of similar structure and composition. Further evidence is presented that the bulk oxidation state of cobalt in the CoCF is 3+. We propose that the catalyst film is composed of interconnected complete and/or incomplete Co-oxo cubanes possibly forming a disordered network of the basic Co_3/4(μ-O)₄ units.

It has been shown that Pt₃Co nanoparticles used as a catalyst for cathode of Proton Exchange Membrane Fuel Cells (PEMFC) enhance oxygen reduction reaction (ORR) activity even by a factor of two compared to pure Pt nanoparticles. The local structure and chemical disorder of a commercially available Pt₃Co nanocatalyst supported on high surface area carbon were investigated. High-quality XAFS spectra were collected at the ELETTRA synchrotron XAFS 11.1 beamline. XAFS spectra analysis have been performed accounting for the reduction of the coordination number and degeneracy of three-body configurations, resulting from transmission electron microscopy (TEM) and x-ray diffraction (XRD) extracted mean particles diameter, size distribution and expected surface atom contributions. The presence of a Co-Co first neighbour EXAFS signal is shown to be related to the degree of the alloy's chemical disorder. This is a good starting point for analyzing the atomic structure of Pt₃Co nanocrystalline system and their changes as a function of alloy preparation or working conditions when they operate as a catalyst in PEMFC.

SiO₂-Supported Fe-NbN catalysts were prepared by temperature programmed reaction (TPR) method from Fe-Nb/SiO₂ oxide precursor under a N₂-H₂ gas stream. As raising the intermediate temperature-maintaining (ITM) step temperature during the TPR, Fe species in the Fe-Nb/SiO₂ catalyst was reduced to zero-valent, confirmed by Fe K-edge XAFS analysis. Although the Fe-Fe coordination number increased by elevating ITM temperature, the size of Fe cluster was still small. The Nb-N coordination number became larger, as higher the ITM temperature. The reduced Fe species effectively assisted the nitridation process of Nb.

Dynamical change of structure of Rh supported on H-USY and Na-USY zeolite was measured by Quick XAFS technique operated under in situ conditions. In the atmosphere of H2, formation of the Rh clusters consist of 13 atoms was observed in H-USY and Na-USY. On the other hand, in the atmosphere of O₂, formation of the highly dispersed Rh oxide was observed in H-USY, whereas Rh oxide species did not disperse in Na-USY. In the reduction processes after heating samples in the atmosphere of O₂, the highly dispersed metal Rh particles in the H-USY agglomerated with increasing temperature above 553K. Whereas, the generation of stable Rh clusters were observed on the Na-USY. From these finding, it was conclude that the structure and acid sites of USY affected on the dispersion of Rh oxide particles and the generation of metal Rh clusters.

Chemical state analysis of silver species in Ag⁺ exchanged zeolite A and Y catalysts were carried out by means of XAFS and UV-Vis spectroscopies. Order of thermal stability of silver cluster was Ag(50%)-Y > Ag(60%)-A > Ag(100%)-A, which was consistent with the previous ¹H NMR study for stability of chemisorbed hydrogen species. The three shell model (Ag-O, Ag-Ag, and Ag-Al/Si) of silver cluster in zeolites was proposed.

In situ X-ray absorption spectroscopy at the Pd L₃ edge was applied to determine the particle size effect on the formation of palladium hydride and on surface hydrogen adsorption at room temperature. Pd L₃ edge XANES spectra allow direct detection of hydride formation via a characteristic spectral feature caused by the formation of a Pd-H anti-bonding state. This feature showed strong particle size dependence. The L₃ edge spectra were reproduced using full multiple scattering analysis and density of states calculations and the contributions of bulk-dissolved and surface hydrogen to the XANES spectra could be distinguished. The ratio of hydrogen on the surface versus that in the bulk increased with decreasing particle size, and smaller particles dissolved less hydrogen.

The unique features of X-ray absorption spectroscopy allow investigations of nanosized catalysts for fuel cells under working conditions. We present the results of an experiment carried out on a low Pt content electrocatalyst supported by a mesoporous heteropolyacid salt and used at the cathode of a proton exchange membrane fuel cell (PEMFC). The analysis of the EXAFS signal at the Pt L₃-edge indicates that upon operating the fuel cell a substantial oxygen desorption from the Pt catalytic surface occurs followed by a tangible structural change on the Pt local order.

Phosphorus, a group V element, has always been found so far in minerals, biological systems and synthetic compounds with an oxygen coordination number of four (i.e, PO₄ groups). We demonstrate here using phosphorus K-edge XANES spectroscopy that this element can also adopt a six-fold oxygen coordination (i.e, PO₆ groups). This new coordination was achieved in AlPO₄ doped SiO₂ stishovite synthesized at 18 GPa and 1873 K and quenched down to ambient conditions. The well-crystallized P-bearing stishovite grains (up to 100μm diameter) were embedded in the back-transformation products of high pressure form of AlPO₄ matrix. They were identified by elemental mapping (μ-XRF). μ-XANES spectra collected at the Si and P K edges in the Si rich region with a very low concentration of P present striking resemblance, Si itself being characteristic of pure stishovite. We can therefore infer that phosphorus in the corresponding stishovite crystal is involved in an octahedral coordination made of six oxygen atoms. First principle XANES calculations using a plane-wave density functional formalism with core-hole effects treated in a supercell approach at the P K edge for a P atom substituting an Si one in the stishovite structure confirm this assertion. This result shows that in the lower-mantle where all silicon is six-fold coordinated, phosphorus has the crystal-chemical ability to remain incorporated into silicate structures.

A selection of marine biominerals, mostly aragonitic coral skeletons were probed at the Mg K-edge by XANES spectroscopy coupled to μXRF methods and compared to an extensive set of relevant model compounds (silicates, carbonates, oxides and organic). Extensive methodologies are required to better describe the speciation of Mg in those minerals. A combination of ab-initio XANES calculations for defective clusters around Mg in aragonite together with wavelets analyzes of the XANES region are required to robustly interpret the spectra. When using those methodologies, the speciation of Mg ranges from a magnesite-type environment in some scleractinian corals to an organic-type environment. In all environments, the Mg-domains probed appear to be less than 1 nm in size.

High-resolution XANES spectra for various chromates show that their pre-edge feature varies dramatically with Cr-polymerization. Ab-initio FEFF calculations reproduces those observed experimental trends. Those variations can be easily explained with Pauling's bond valence rules. As chromates are used to model the fraction of toxic Cr(VI) in samples of environmental importance (among others), a careful choice of the chromate model compound is essential for a reliable model of the Cr-speciation in "unknown" samples.

Powders of four synthetic glasses of volcanic composition, a silica glass and crystalline quartz were equilibrated with SO₂ to study the speciation of S sorbed onto their surface. These samples mimic the aerosols injected into the atmosphere during volcanic eruptions. Volcanic sulfur is known to globally affect the Earth's climate with an opposite effect to CO₂. However, absorption on ashes may reduce the amount of sulfur entering the stratosphere. S K-edge micro-XANES (μXANES) spectra and μXRF maps were collected at the LUCIA beamline (SOLEIL) at the SLS (Switzerland). When photoreduction is minimized, SO₂ is sorbed mostly as sulfates moieties. The sorption of S is controlled by the surface structure of the powders probed. Presence of defects, non-bridging oxygens and network-modifiers (alkali and alkali-earths) enhance S-sorption as sulfate moieties onto the powders surface. Therefore, the quantity of S released to the atmosphere is highly dependant on the type of ash produced during eruptions that help to better model the climatic impact of volcanic S.

We present structural information obtained on spinel at high temperature (298–2400 K) using in situ XANES at the Mg and Al K-edge. Spinel, ^[4](Al_x,Mg_1-x)^[6](Al_2-x,Mg_x)O₄, with increasing temperature, show a substitution of Mg by Al and Al by Mg in their respective sites. This substitution corresponds to an inversion of the Mg and Al sites. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.

This study is focused on the determination of the geochemical behaviour of europium (Eu) in a set of synthetic silicate glasses with composition relevant for the Earth Science and ranging from basaltic to granitic composition. The samples have been characterized through Eu L_III-edge by X-ray Absorption Spectroscopy (XAS) and the measurements have been performed in fluorescence mode at the ESRF (Grenoble, F). Eu L_III-edge XANES analysis allowed to obtain a semi-quantitative assessment of the Eu²⁺/(Eu²⁺ + Eu³⁺) redox ratio.

Kinetics of europium reduction at low oxygen fugacity (IW buffer) has been studied on samples equilibrated at different times. Data obtained from kinetic experiments clearly show that glasses of basaltic composition reach equilibrium values of the Eu²⁺/(Eu²⁺ + Eu³⁺) ratio after 6 h at 1400 ° C, whereas glasses of granitic composition reach equilibrium after 60 h at 1400 ° C. Knowledge of Eu reduction kinetics is an absolute prerequisite for any study of Eu oxidation state at low oxygen fugacity.

Pb-L_III edge XANES and μ-XAFS experiments (bulk and μ-focalised) were performed to evaluate the speciation of radiogenic Pb in naturally irradiated monazites (ideally LaPO₄) and zircons (ideally ZrSiO₄) minerals after ca. one billion years. XANES spectra show that Pb is divalent in all the samples investigated. But large variation in the speciation of Pb has been evidenced from monazites to zircons. Ab-initio calculations (FEFF8.4) were preliminary tested in a set of Pb-sulfide, oxide, carbonate, phosphate and silicate minerals and converged using Dirac-Hara exchange potentials. In monazite, XANES spectra calculations results are consistent with Pb substituting to La.

The experimental Ti K-edge X-ray absorption near edge structure (XANES) spectrum of the mineral ilmenite was recorded. The theoretical Ti K-XANES spectra of ilmenite were simulated using both the self-consistent real-space full-multiple scattering theory within the muffin-tin approximation for the potential shape and the full-potential finite difference method. The comparison of the theoretical spectra with the experimental XANES is discussed. The electronic structure of ilmenite was investigated by analyzing the distribution of the partial densities of electron states.

In Earth and Materials sciences, iron is the most important transition element. Glass and melt properties are strongly affected by iron content and redox state with the consequence that some properties (i.e. viscosity, heat capacity, crystallization...) depend not only on the amounts of Fe²⁺ and Fe³⁺, but also on the coordination state of these ions. In this work we investigate iron redox reactions through XANES experiments at the K-edge of iron. Using a high-temperature heating device, pre-edge of XANES spectra exhibits definite advantages to make in-situ measurements and to determine the evolution of redox state with time, temperature and composition of synthetic silicate melts. In this study, new kinetics measurements are presented for a basalt melt from the 31,000-BC eruption of the Puy de Lemptegy Volcano in France. These measurements have been made between 773 K and at superliquidus temperatures up to 1923 K.

Trace chlorinated organic compounds are generated via thermal processes. Their formation is promoted by copper chloride in solid phase such as fly ash, especially in the post-combustion zone in municipal solid waste incineration. Previously, we reported the chemical state and change of copper chloride in a single model using the in situ quick scan x-ray absorption fine structure (QXAFS). However, a real solid phase, which is a complex system involving many elements, was not simulated. In this paper, we measured the Cu-K XAFS of a metal-mixture model upon heating to discuss the effect of mixing. The in situ QXAFS technique revealed that the reaction temperature of copper was lower, compared with the single model, when a mixture was measured. The result shows that the formation mechanism of chlorinated organic compounds derived from anthropogenic thermal sources can be described more correctly.

Sulfur is an essential biological element, yet its biochemistry in anaerobic biofilm is poorly understood because there are few tools for studying this element in biological systems. X-ray absorption spectroscopy provides a unique approach to determining the chemical speciation of sulfur in intact biological samples. When treating sulfate containing wastewaters in full scale up-flow anaerobic sludge bed bioreactors, microbial activity forms biofilms, consisting of a complex mixture of cells and associated extracellular substances as well as undefined inorganic precipitates. In addition to the anaerobic sludges, a large variety of model compounds of S (esp. sulfides) were investigated to find consistencies in the XANES that were used to model each "valence state" of S. The results confirmed that attributing a specific valence to most sulfides is impossible as we measured a continuum of edge shifts from sulfur "-2" to "-1", depending on the electronic structure of S in the probed sulfides. In the sludges, various sulfur hot spots were probed for speciation, despite photo-reduction was sometimes a problem. First, we index the main features of complex K-edge XANES spectra for S^2--type units and sulfate units. Organic sulfur compounds were also shown to contribute significantly to the sulfur species present in some anaerobic granular sludge.

The complexation of thorium, neptunium and plutonium at oxidation state +IV with three ligands of increasing complexity has been investigated. These ligands are relevant for bio inorganic systems. The first ligand is the small nitrilotriacetic acid that often play the role of protecting ligands against hydrolysis. EXAFS results for the Th to Pu series have been correlated to quantum chemical calculations and show an homogeneous behavior of the actinide at oxidation state +IV. For larger ligands, steric effects may become significant and one can ask how the ligand may accommodate the large actinide cation coordination sphere. Model pentapeptides have been synthesized and tested as complexing agents. Comparison with NTA shows that the molecular arrangements are radically different. The third ligand system is transferrin, a diferric metalloptrotein that is well known to coordinate a large variety of cations from transition metals of f-elements. Metalloproteins bear primary, secondary and tertiary structures that all play a crucial role in bonding. At a given oxidation state (+IV), but for various atomic numbers (Th, Np, Pu) EXAFS data at the cation L_III edge exhibit significant coordination discrepancies that are related to a changes in protein geometry. In that sense, the metalloprotein may be viewed as a complex system.

We perform X-ray absorption fine structure (XAFS) spectroscopy measurements at the sulfur K-edge to elucidate the electronic and geometric bonding of sulfur atoms in borosilicate glass used for the vitrification of high level radioactive liquid waste. The sulfur is incorporated as sulfate, most probably as sodium sulfate, which can be deduced from the X-ray absorption near edge structure (XANES) by fingerprint comparison with reference compounds. This finding is backed up by Raman spectroscopy investigation. In the extended XAFS data, no second shell beyond the first oxygen layer is visible. We argue that this is due to the sulfate being present as small clusters located into voids of the borosilicate network. Hence, destructive interference of the variable surrounding prohibits the presence of higher shell signals. The knowledge of the sulfur bonding characteristics is essential for further optimization of the glass composition and to balance the requirements of the process and glass quality parameters, viscosity and electrical resistivity on one side, waste loading and sulfur uptake on the other side.

Combined spatially resolved hard X-ray μ-XRF and μ-XAFS studies using an X-ray beam with micrometer dimensions at the INE-Beamline for actinide research at ANKA and Beamline L at HASYLAB with those from scanning transmission soft X-ray microscopy (STXM) and synchrotron-based Fourier transform infrared microspectroscopy (μ-FTIR) recorded with beam spots in the nanometer range are used to study a U-rich clay originating from Autunian shales in the Permian Lodève Basin (France). This argillaceous formation is a natural U deposit associated with organic matter (bitumen). Results allow us to differentiate between possible mechanisms leading to U enrichment: likely U immobilization via reaction with organic material associated with clay mineral. Such investigations support development of reliable assessment of the long term radiological safety for proposed nuclear waste disposal sites.

The long term radiotoxicity of spent nuclear fuel disposed of in deep underground repositories after discharge from nuclear power reactors is determined by actinide elements, mainly plutonium. Water intrusion into the repository might cause container corrosion and leaching of the waste matrices, leading to the release of Pu and other actinides into the geological environment. Performance assessment for a future nuclear waste repository requires detailed knowledge on actinide aqueous chemistry in the aquifer surrounding the disposal site. Tetravalent actinides exhibit a strong tendency towards hydrolysis and subsequent polymerization and/or colloid formation. These species provide a potential pathway for migration of actinides away from the repository. Therefore, it is of fundamental interest to study their generation and properties in-situ. To this end, X-ray Absorption Fine Structure Spectroscopy (XAFS) at the INE-Beamline for actinide research at ANKA, Electrospray Mass-Spectrometry (ESI TOF-MS) and Laser Induced Breakdown Detection (LIBD) are combined at FZK-INE in a comprehensive attempt to characterize Zr(IV) (An(IV) analogue), Th(IV) and Pu(IV) polymerization and colloid formation.

We present a study about the behavior of Zn in agricultural soils polluted 100–50 years ago by metallurgical fallout and used nowadays for corn production. Such type of soil concerns an area of several km² around former metallurgical complex in Northern France. Despite the moderated metal amounts of these soils, the metals deposited over the agricultural area still indirectly expose nowadays populations through the food chain. In contrast to the most contaminated industrial site, these more distant agricultural areas have been less studied. The study was focused on Zn, a relative mobile metal element, since its predominant occurrence in the surface horizon of sandy textured soils, fifty years after cessation of metallurgical activity suggests its immobilization due to specific soil mechanisms. To evaluate how Zn is associated to POM, Zn K-edge XAFS spectra were collected at 293 K at the SLS on beamlines superXAS and microXAS, using Si(111) monochromators and solid state Ge detectors. Energetic resolution is ca. 2 eV at 9 KeV. Lateral resolution varied from ca. 1 mm² to 15 micron². Spectra were normalized with the XAFS 3.0 software. We studied different POM size fractions isolated from soils. The largest POM particles correspond to recent leaves or roots fragments. The finest POM particles correspond to decomposition by-products. The results revealed a multiple and heterogeneous speciation of Zn with POM. We observed that little interactions from next-nearest neighbors around Zn. We concluded that most of the Zn tends to be located in the POM matrix as a Zn-organic speciation. We also collected macroscopic EXAFS data on selected intact POM particles probed at the micron scale. The results show that the remaining Zn-distribution related to inorganic (hot-spots), possibly franklinite-type, is minor compared to the Zn-organic speciation. Such observations will help to better understand the mechanisms that regulate the bioavailability and immobilization of Zn in polluted soils.