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We report here a detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with a high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the U M4 edge. We show the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. Calculations based on density functional theory and on crystal field multiplet theory indicate that for all local configurations analyzed, the main peak corresponds to nonbonding 5f orbitals, and the highest energy peak corresponds to antibonding 5f orbitals. Our findings agree with the accepted interpretation of uranyl spectral features and embed the latter in a broader field of view, which interprets the spectra of a large variety of U6+-containing samples on a common theoretical ground.

V–W/TiO$_{2}$-based catalysts, which are used for the removal of NO$_{x}$ from the exhaust of diesel engines and stationary sources via selective catalytic reduction with NH$_{3}$ (NH$_{3}$-SCR), were studied by operando X-ray absorption spectroscopy (XAS) and emerging photon-in/photon-out techniques. In order to minimize the influence of highly X-ray absorbing tungsten and the fluorescence of titanium, we used a high-energy-resolution fluorescence setup that is able to separate efficiently the V Kβ$_{1,3}$ emission lines and additionally allows to record valence-to-core (vtc) X-ray emission lines. High-energy resolution fluorescence-detected XAS (HERFD-XAS) and vtc X-ray emission spectroscopy (vtc-XES) proved to be the only way to perform an operando V K edge X-ray spectroscopic study on industrially relevant V–W/TiO$_{2}$ catalysts so far. The V–W/TiO$_{2}$ and V/TiO$_{2}$ samples synthesized by incipient wetness impregnation and grafting exhibited high activity toward NH$_{3}$-SCR. Raman spectroscopy showed that they mainly contained highly dispersed, isolated, and polymeric V-oxo species. HERFD-XAS and XES identified redox cycling of vanadium species between V$^{4+}$ and V$^{5+}$. With respect to most of the potential NH$_{3}$ adsorption complexes, density functional theory calculations further showed that vtc-XES is more limited than surface-sensitive techniques such as infrared spectroscopy; hence, a combination of X-ray techniques with IR or similar spectroscopies is required to unequivocally identify the mechanism of NH$_{3}$-SCR over vanadia-based catalysts.

Developing characterization techniques and analysis methods adapted to the investigation of nanoparticles (NPs) is of fundamental importance considering the role of these materials in many fields of research. The study of actinide based NPs, despite their environmental relevance, is still underdeveloped compared to that of NPs based on stable and lighter elements. We present here an investigation of ThO2 NPs performed with High-Energy Resolution Fluorescence Detected (HERFD) X-ray Absorption Near-Edge Structure (XANES) and with ab initio XANES simulations. The first post-edge feature of Th L3 edge HERFD XANES disappears in small NPs and simulations considering non-relaxed structural models reproduce the trends observed in experimental data. Inspection of the simulations from Th atoms in the core and on the surface of the NP indeed demonstrates that the the first post-edge feature is very sensitive to the lowering of the number of coordinating atoms and therefore to the more exposed Th atoms at the surface of the NP. The sensitivity of the L3 edge HERFD XANES to low coordinated atoms at the surface stems from the hybridization of the d-Density of States (DOS) of Th with both O and Th neighboring atoms. This may be a common feature to other oxide systems that can be exploited to investigate surface interactions.

Invited for the cover of this issue is Lucia Amidani and co-workers from the The European Synchrotron, Helmholtz Zentrum Dresden-Rossendorf, Lomonosov Moscow State University, Kurchatov Institute, and the Université Grenoble Alpes. The image depicts the atomic structure of the sample being viewed through "atomic googles", which represent the X-ray techniques used in this work. Read the full text of the article at 10.1002/chem.202003360.

Eu$^{2+}$ is used to replace toxic Pb$^{2+}$ in metal halide perovskite nanocrystals (NCs). The synthesis implies injection of cesium oleate into a solution of europium (II) bromide at an experimentally determined optimum temperature of 130C and a reaction time of 60s. Structural analysis indicates the formation of spherical CsEuBr$_3$ nanoparticles with a mean size of 43nm. Using EuI$_2$ instead of EuBr$_2$ leads to the formation of 18nm CsI nanoparticles, while EuCl$_2$ does not show any reaction with cesium oleate forming 80nm EuCl2 nanoparticles. The obtained CsEuBr3 NCs exhibit bright blue emission at 413nm (FWHM 30 nm) with a room temperature photoluminescence quantum yield of 39%. The emission originates from the Laporte-allowed 4f7-4f65d1 transition of Eu$^{2+}$ and shows a PL decay time of 263ns. The long-term stability of the optical properties is observed, making inorganic lead-free CsEuBr$_3$ NCs promising deep blue emitters for optoelectronics., The Journal of Chemical Physics (2019)

Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and contaminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III), and Eu(III) than standard graphene oxides (GOs). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. Therefore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with a large number of defects and holes. Defects and holes are additionally introduced by Hummers oxidation of rGO, thus providing an extremely defect-rich material. Analysis of characterization by XPS, TGA, and FTIR shows that dGO oxygen functionalization is predominantly related to defects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to that in standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic group attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy.

Laser excitation and x-ray spectroscopy are combined to settle a long-standing question in persistent luminescence. A reversible electron transfer is demonstrated, controlled by light and showing the same kinetics as the persistent luminescence. Exposure to violet light induces charging by oxidation of the excited Eu^{2+} while Dy^{3+} is simultaneously reduced. Oppositely, detrapping of Dy^{2+} occurs at ambient temperature or by infrared illumination, yielding afterglow or optically stimulated luminescence, respectively.

The nanoscience field often produces results more mystifying than any other discipline. It has been argued that changes in the plutonium dioxide (PuO

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany., RSC Advances (2020)

The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized byHummers’s, Brodie’s and Tour’s methods was studied through a combination of batch experiments withcharacterization by microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy(XPS), attenuated total reflection fourier-transform infrared spectroscopy (ATR-FTIR), high-energy resolutionfluorescence detected X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorptionfine structure (EXAFS) and high resolution transmission electron microscopy (HRTEM). Remarkablydifferent sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers’sand Brodie’s methods reflecting different structure and oxidation state of these materials.Mechanism underlying GO e radionuclide interaction is determined using variety of experimentaltechniques. For the first time it is shown here that GO - radionuclides interaction takes place on the smallholes or vacancy defects in the GO sheets. Mechanism of GO’s interaction with radionuclides wasanalyzed and specific functional groups responsible for this interaction were identified. Therefore, a newstrategy to produce improved materials with high capacity for radionuclides suggests the use perforatedand highly defected GO with a larger proportion of carboxylic functional groups.

In order to optimize the catalytic functionality of cerium oxide it is important to understand the structural modifications associated with reduction of the material and the role of the proximity of metals, which are often coupled with the oxide in the applications. For this purpose, the evolution of the short- and long-range structure of cerium oxide ultrathin epitaxial films and nanostructures supported on Pt(111) is investigated using x-ray absorption spectroscopy at the Ce L3 edge and surface x-ray diffraction, during reduction by thermal treatments in vacuum. In epitaxial nanoislands, the reduction is associated with a contraction of the Ce-O distance and with the appearance of Ce-Pt bonds. The formation of a phase with a (2×2) periodicity after a thermal treatment at 1023 K is ascribed to the formation of a Pt5Ce alloy. Films of 3 nm thickness do not show, on average, significant structural modifications with the same thermal treatment, consistent with the hypothesis that the reduction involves only the topmost surface layers and it does not influence significantly the bulk structure of the material. This study demonstrates a strong interaction between cerium oxide and platinum, which has implications for the reactivity and stability of catalysts based on metals combined with reducible oxides.

Synchrotron radiation (SR)-based X-ray methods are powerful analytical tools for several purposes and we widely use them for probing the degradation mechanisms of inorganic artists’ pigments in paintings, including chrome yellows (PbCr1-xSxO4; 0 ≤x≤0.8), a class of compounds often found in Van Gogh masterpieces. However, the high intensity and brightness of SR beams raise important issues regarding potential damages of the analyzed samples. A thorough knowledge of the SR X-ray sensitivity of each class of pigment in the painting matrix is therefore required to find analytical strategies that contribute to minimize the damage for preserving the integrity of the analyzed sample and to avoid misinterpretation of the data. Here, we employ a combination of Cr K-edge X-ray absorption near edge structure (XANES) spectroscopy, Cr-Kβ X-ray emission spectroscopy (XES) and X-ray diffraction (XRD) to monitor and quantify the effects of SR X-rays on the stability of chrome yellows and related Cr-compounds and to define strategies for mitigating their damage. We found that the SR X-ray beam exposure induces changes in the oxidation state and local coordination environment of Cr-ions and leads to a loss of the compound’s crystalline structure. The extent of X-ray damage depends on some intrinsic properties of the samples (chemical composition of the pigment as well as the presence/absence and nature of the binder) and it can be minimized by optimizing the overall fluence/dose released to the samples and by working in vacuum and cryogenic conditions.

Hematite (alpha-Fe2O3) is an earth-abundant indirect n-type semiconductor displaying a band gap of about 2.2 eV, useful for collecting a large fraction of visible photons, with frontier energy levels suitably aligned for carrying out the photo-electrochemical water oxidation reaction under basic conditions. The modification of hematite mesoporous thin- film photoanodes with Ti(IV), as well as their functionalization with an oxygen-evolving catalyst, leads to a 6-fold increase in photocurrent density with respect to the unmodified electrode. In order to provide a detailed understanding of this behavior, we report a study of Ti-containing phases within the mesoporous film structure. Using X-ray absorption fine structure and high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy, we find that Ti(IV) ions are incorporated within ilmenite (FeTiO3) near-surface layers, thus modifying the semiconductor-electrolyte interface. To the best of our knowledge, this is the first time that an FeTiO3/-Fe2O3 composite is used in a photoelectrochemical setup for water oxidation. In fact, previous studies of Ti(IV)modified hematite photoanodes reported the formation of pseudobrookite (Fe2TiO5) at the surface. By means of transient absorption spectroscopy, transient photocurrent experiments, and electrochemical impedance spectroscopy, we show that the formation of the Fe2O3/FeTiO3 interface passivates deep traps at the surface and induces a large density of donor levels, resulting in a strong depletion field that separates electron and holes, favoring hole injection in the electrolyte. Our results provide the identification of a phase coexistence with enhanced photoelectrochemical performance, allowing for the rational design of new photoanodes with improved kinetics.

Eu

International audience; This study deals with the unprecedented reactivity of dinuclear non-heme MnII -thiolate complexes with O2 , which dependent on the protonation state of the initial MnII dimer selectively generates either a di-μ-oxo or μ-oxo-μ-hydroxo MnIV complex. Both dimers have been characterized by different techniques including single-crystal X-ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled 18 O2 unambiguously show that the oxygen atoms present in the MnIV dimers originate from O2 . Based on experimental observations and DFT calculations, evidence is provided that these MnIV species comproportionate with a MnII precursor to yield μ-oxo and/or μ-hydroxo MnIII dimers. Our work highlights the delicate balance of reaction conditions to control the synthesis of non-heme high-valent μ-oxo and μ-hydroxo Mn species from MnII precursors and O2 .

Developing characterization techniques and analysis methods adapted to the investigation of nanoparticles (NPs) is of fundamental importance considering the role of these materials in many fields of research. The study of actinide based NPs, despite their environmental relevance, is still underdeveloped compared to that of NPs based on stable and lighter elements. We present here an investigation of ThO

WO

In order to optimize the performance of devices based on porphyrin thin films it is of great importance to gain a physical understanding of the various factors which affect their charge transport and light-harvesting properties. In this work, we have employed a multi-technique approach to study vacuum deposited zinc octaethyl porphyrin (ZnOEP) thin films with different degrees of long-range order as model systems. An asymmetrical stretching of the skeletal carbon atoms of the porphyrin conformer has been observed and attributed to ordered molecular stacking and intermolecular interactions. For ordered films, a detailed fitting analysis of the X-ray absorption near edge structure (XANES) using the MXAN code establishes a symmetry reduction in the molecular conformer involving the skeletal carbon atoms of the porphyrin ring; this highlights the consequences of increased π-π stacking of ZnOEP molecules adopting the triclinic structure. The observed asymmetrical stretching of the π conjugation network of the porphyrin structure can have significant implications for charge transport and light harvesting, significantly influencing the performance of porphyrin based devices.

WO3/BiVO4 films obtained by electrochemical deposition of BiVO4 over mesoporous WO3 were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO3/BiVO4 films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na2SO4 electrolytes. Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO3/BiVO4 junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO3/BiVO4 interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO4 and a different water oxidation mechanism, the employment of WO3/BiVO4 in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO2 and WO3.

Incorporation of dopants in semiconductors is commonly used to modify the optical response and improve the efficiency of related devices. A physical understanding with elemental and local sensitivity of the electron excitation and trapping channels which follow photoexcitation is a prerequisite for knowledge-based materials design. By using high-resolution x-ray absorption methods we show that, in V-doped TiO2 nanoparticles, subband-gap visible light absorption is predominantly due to excitation of electrons from V ions to defective and long-lived Ti sites. We thus identify an element-specific photoexcitation channel.

Doping with transition metals is an effective method to enhance visible-light absorption in TiO2 nanoparticles and to improve the efficiency of many photocatalytic processes under solar radiation. A determination of the incorporation site of the dopant and an understanding of the local bonding arrangement and electronic structure is a necessary step for knowledge-based materials design. In this paper, we report an in-depth X-ray absorption spectroscopy study of V dopants in TiO2 nanoparticles deposited by gas-phase condensation with a local structure similar to anatase, rutile, or intermediate. The combination of K- and L-edge spectra in the pre-edge, edge, and extended energy regions with full potential ab initio spectral simulations shows that V ions occupy substitutional cationic sites in the TiO2 structure, irrespective of whether it is similar to rutile, anatase, or mixed.

The structural characterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non-homogeneous samples with NPs less than 3 nm. By combining high-energy X-ray scattering (HEXS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD XANES) analysis, we have characterised for the first time both the short- and medium-range order of ThO2 NPs obtained by chemical precipitation. By using this methodology, a novel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution function revealed a high concentration of ThO2 small units similar to thorium hexamer clusters mixed with 1 nm ThO2 NPs in the initial steps of formation. Drying the precipitates at around 150 °C promoted the recrystallisation of the smallest units into more thermodynamically stable ThO2 NPs. HERFD XANES analysis at the thorium M4 edge, a direct probe for f states, showed variations that we have correlated with the breakdown of the local symmetry around the thorium atoms, which most likely concerns surface atoms. Together, HEXS and HERFD XANES are a powerful methodology for investigating actinide NPs and their formation mechanism.

The addition of cerium oxide to bioactive glasses, important materials for bone tissue regeneration, has been shown to induce multifunctionality, combining a significant bioactivity with antioxidant properties. We provide a real time investigation of the evolution of the electronic properties of highly diluted cerium ions in a liquid environment containing hydrogen peroxide - the most abundant reactive oxygen species in living cells. This challenging task is undertaken by means of high-energy resolution fluorescence detected by X-ray absorption near-edge spectroscopy at the Ce L3 edge. We investigate samples with variable compositions and different morphologies. We relate the observed spectroscopic changes not only to variations in the concentration of the two Ce oxidation states in the samples, but also to changes in the local atomic environment of Ce ions, providing a clear picture of the role of cerium ions in the dissociation of hydrogen peroxide. The obtained results contribute to the understanding of the mechanisms that come into play in the process and provide a basis for the optimization of the functionalities of this class of materials.

We report an X-ray absorption near edge structure (XANES) study of vanadium (V) and nitrogen (N) dopants in anatase TiO2 thin films deposited by radio-frequency magnetron sputtering. Measurements at the Ti K and V K edges were combined with soft X-ray experiments at the Ti L2,3, O K and N K edges. Full potential ab initio spectral simulations of the V, O and N K-edges were carried out for different possible configurations of substitutional and interstitial dopant-related point defects in the anatase structure. The comparison between experiments and simulations demonstrates that V occupies substitutional cationic sites (replacing Ti) irrespective of the film structure and dopant concentration (up to 4.5 at%). On the other hand, N is found both in substitutional anionic sites (replacing O) and as N2 dimers within TiO2 interstices. The dopants' local structures are discussed with reference to the enhanced optical absorption and photocatalytic activity achieved by (co)doping.

International audience; Solar fuels such as H-2 generated from sunlight and seawater using earth-abundant materials are expected to be a crucial component of a next generation renewable energy mix. We herein report a systematic analysis of the photo-electrochemical performance of TiO2 coated, microstructured p-Si photo-electrodes (p-Si/TiO2) that were functionalized with CoOx and NiOx for H-2 generation. These photocathodes were synthesized from commercial p-Si wafers employing wet chemical methods. In neutral phosphate buffer and standard 1 sun illumination, the p-Si/TiO2/NiOx photoelectrode showed a photocurrent density of -1.48 mA cm(-2) at zero bias (0 V-RHE), which was three times and 15 times better than the photocurrent densities of p-Si/TiO2/CoOx and p-Si/TiO2, respectively. No decline in activity was observed over a five hour test period, yielding a Faradaic efficiency of 96% for H-2 production. Based on the electrochemical characterizations and the high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and emission spectroscopy measurements performed at the Ti K-1 fluorescence line, the superior performance of the p-Si/TiO2/NiOx photoelectrode was attributed to improved charge transfer properties induced by the NiOx coating on the protective TiO2 layer, in combination with a higher catalytic activity of NiOx for H-2-evolution. Moreover, we report here an excellent photo-electrochemical performance of p-Si/TiO2/NiOx photoelectrode in corrosive artificial seawater (pH 8.4) with an unprecedented photocurrent density of 10 mA cm(-2) at an applied potential of -0.7 V-RHE, and of 20 mA cm(-2) at -0.9 V-RHE. The applied bias photon-to-current conversion efficiency (ABPE) at -0.7 V-RHE and 10 mA cm(-2) was found to be 5.1%.

We report an X-ray absorption near edge structure (XANES) study of vanadium (V) and nitrogen (N) dopants in anatase TiO

Exploiting plasmonic Au nanoparticles to sensitize TiO2 to visible light is a widely employed route to produce efficient photocatalysts. However, a description of the atomic and electronic structure of the semiconductor sites in which charges are injected is still not available. Such a description is of great importance in understanding the underlying physical mechanisms and to improve the design of catalysts with enhanced photoactivity. We investigated changes in the local electronic structure of Ti in pure and N-doped nanostructured TiO2 loaded with Au nanoparticles during continuous selective excitation of the Au localized surface plasmon resonance with X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Spectral variations strongly support the presence of long-lived charges localized on Ti states at the semiconductor surface, giving rise to new laser-induced low-coordinated Ti sites.

Phosphorus-fertilizers from secondary resources such as sewage sludge ash (SSA) will become more important in the future as they could substitute conventional fertilizers based on the nonrenewable resource phosphate rock. Thermochemical approaches were developed which remove heavy metals from SSA prior to its fertilizer application on farmlands. We analyzed the chemical state of mercury and selenium in SSA before and after thermochemical treatment under different conditions for P-fertilizer production by X-ray absorption near edge structure (XANES) spectroscopy. In some incineration plants the mercury loaded carbon adsorber from off-gas cleaning was collected together with the SSA for waste disposal. SSAs from those plants contained mercury mainly bound to carbon/organic material. The other SSAs contained inorganic mercury compounds which are most probably stabilized in the SSA matrix and were thus not evaporated during incineration. During thermochemical treatment, carbon-bound mercury was removed quantitatively. In contrast, a certain immobile fraction of inorganic mercury compounds remained in thermochemically treated SSA, which were not clearly identified. HgSe might be one of the inorganic compounds, which is supported by results of Se K-edge XANES spectroscopy. Furthermore, the chemical state of selenium in the SSAs was very sensitive to the conditions of the thermochemical treatment.

The effects of low-energy irradiation by light ions (H and He) on the properties of In-rich InxGa1−xN alloys are investigated by optical and structural techniques. H-irradiation gives rise to a remarkable blue-shift of light emission and absorption edge energies. X-ray absorption measurements and first-principle calculations address the microscopic origin of these effects.

An accurate description of the structural and chemical modifications of cerium oxide nanoparticles (NPs) is mandatory for understanding their functionality in applications. In this work we investigate the relation between local atomic structure, oxidation state, defectivity and size in cerium oxide NPs with variable diameter below 10 nm, using x-ray absorption fine structure analysis in the near and extended energy range. The NPs are prepared by physical methods under controlled conditions and analyzed in morphology and crystalline quality by high resolution transmission electron microscopy. We resolve here an important question on the local structure of cerium oxide NPs: we demonstrate a progressive contraction in the Ce-O interatomic distance with decreasing NP diameter and we relate the observed effect to the reduced dimensionality. The contraction is not significantly modified by inducing a 4%-6% higher Ce3+ concentration through thermal annealing in high vacuum. The consequences of the observed average cation-anion distance contraction on the properties of the NPs are discussed.

We investigated atomic ordering in In-rich In x Ga1−x N epilayers in order to obtain an understanding of whether a deviation from a random distribution of In atoms in the group-III sublattice could be the origin of the strong carrier localization and defect-insensitive emission of these semiconductor alloys. This phenomenon can be exploited for application in optoelectronics. By coupling In K-edge x-ray absorption spectroscopy and high resolution x-ray diffraction, we were able to discard the hypothesis of significant phase separation into InN + GaN, in agreement with previous N K-edge absorption spectroscopy. However, we found an enrichment of In neighbours in the second atomic shell of In as compared to random statistics (clustering) for x = 0.82, while this is not the case for x = 0.46. This result, which is also supported by optical spectroscopy, is likely to stimulate new theoretical studies on In x Ga1−x N alloys with a very high In concentration.

Postgrowth hydrogen incorporation in In-rich In${}_{x}$Ga${}_{1\ensuremath{-}x}$N ($xg0.4$) alloys strongly modifies the optical and structural properties of the material: A large blueshift of the emission and absorption energies is accompanied by a remarkable broadening of the interatomic-distance distribution, as probed by synchrotron radiation techniques. Both effects vanish at a finite In-concentration value ($x$ \ensuremath{\sim} 0.5). Synergic x-ray absorption measurements and first-principle calculations unveil two different defective species forming upon hydrogenation: one due to the high chemical reactivity of H, the other ascribed to mere lattice damage. In the former species, four H atoms bind to as many N atoms, all nearest-neighbors of a same In atom. The stability of this peculiar complex, which is predicted to behave as a donor, stems from atomic displacements cooperating to reduce local strain.

We describe a soft x-ray appearance potential spectroscopy apparatus, which uses a windowless hyperpure Ge detector operated in the photon counting mode. Direct comparisons of recorded spectra with the self-convolution of x-ray absorption spectra and with ab initio simulations in the multiple scattering framework are reported and discussed.

The surface of ferromagnetic Zn1−xCoxO wurtzite epilayers has been studied by coupling atomic force microscopy and advanced x-ray spectroscopy. We found that, even in high-quality epilayers, the formation of Co clusters and iso-space-group Co-rich regions can take place at the sample surface while the bulk maintains random Co distribution. Comparing structural characterization with magnetometry, we show that these surface modifications are not at the origin of the magnetic properties of the material. Quite the reverse, ferromagnetic behavior is enhanced in the sample characterized by the less defective surface.

Although it is well known that dilute species often significantly modify the properties of solids in which they are hosted, a basic question remains open: how critical are their local properties in determining the macroscopic ones of the host material? Here, we address this issue by taking N in dilute III-V-N alloys as a paradigmatic case and propose an original approach based on synergic use of x-ray spectroscopies (XANES and valence – to – core XES at the N K-edge), density functional theory simulations and hydrogen exposure as a tool to modify N local bonding. Our results disclose the key role of the local N – Ga interactions in determining both N-related band states and the macroscopic effects of dilute N on the GaAs energy gap. The success of our approach indicates a new way to connect local and macroscopic properties.

Here we provide evidence that the formation of PuO2 nanoparticles from oxidized PuVI under alkaline conditions proceeds through the formation of an intermediate PuV solid phase, similar to NH4PuO2CO3, which is stable over a period of several months. For the first time, state‐of‐the‐art experiments at Pu M4 and at L3 absorption edges combined with theoretical calculations unambiguously allow to determine the oxidation state and the local structure of this intermediate phase. Early View: Online Version of Record before inclusion in an issue