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Chemical composition of interfaces between physical-vapor-deposited TiN and SiO2 as affected by introduction of a thin (0.5–3 nm) alumina interlayer was studied using photoelectron spectroscopy wit...

Simultaneous retention of SMM behaviour and of optical activity is demonstrated upon surface deposition for a chiral SMM., The synthesis and characterization of a chiral, enneanuclear Mn(iii)-based, Single-Molecule Magnet, [Mn9O4(Me-sao)6(L)3(MeO)3(MeOH)3]Cl (1; Me-saoH2 = methylsalicylaldoxime, HL = lipoic acid) is reported. Compound 1 crystallizes in the orthorhombic P212121 space group and consists of a metallic skeleton describing a defect super-tetrahedron missing one vertex. The chirality of the [MnIII9] core originates from the directional bridging of the Me-sao2– ligands via the –N–O– oximate moieties, which define a clockwise (1ΔΔ) or counter-clockwise (1ΛΛ) rotation in both the upper [MnIII3] and lower [MnIII6] subunits. Structural integrity and retention of chirality upon dissolution and upon deposition on (a) gold nanoparticles, 1@AuNPs, (b) transparent Au(111) surfaces, 1ΛΛ@t-Au(111); 1ΔΔ@t-Au(111), and (c) epitaxial Au(111) on mica surfaces, 1@e-Au(111), was confirmed by CD and IR spectroscopies, mass spectrometry, TEM, XPS, XAS, and AFM. Magnetic susceptibility and magnetization measurements demonstrate the simultaneous retention of SMM behaviour and optical activity, from the solid state, via dissolution, to the surface deposited species.

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Physical chemistry, chemical physics 22(36), 20311 - 20330 (1-20) (2020). doi:10.1039/D0CP04033A, Permanganate aqueous solutions, MnO$_4$$^-$(aq.), were studied using liquid-micro-jet-based soft X-ray non-resonant and resonant photoelectron spectroscopy to determine valence and core-level binding energies. To identify possible differences in the energetics between the aqueous bulk and the solution-gas interface, non-resonant spectra were recorded at two different probing depths. Similar experiments were performed with different counter ions, Na$^+$ and K$^+$, with the two solutions yielding indistinguishable anion electron binding energies. Our resonant photoelectron spectroscopy measurements, performed near the Mn L$_{II,III}$- and O K-edges, selectively probed valence charge distributions between the Mn metal center, O ligands, and first solvation shell in the aqueous bulk. Associated resonantly-enhanced solute ionisation signals revealed hybridisation of the solute constituents’ atomic orbitals, including the inner valence Mn 3p and O 2s. We identified intermolecular Coulombic decay relaxation processes following resonant X-ray excitation of the solute that highlight valence MnO$_4$$^-$$_{(aq.)}$-H$_2$O$_{(l)}$ electronic couplings. Furthermore, our results allowed us to infer oxidative reorganisation energies of MnO$_4$$^•$$_{(aq.)}$ and adiabatic valence ionisation energies of MnO$_4$$^-$$_{(aq.)}$, revealing the Gibbs free energy of oxidation and permitting estimation of the vertical electron affinity of MnO$_4$$^•$$_{(aq.)}$. Finally, the Gibbs free energy of hydration of isolated MnO$_4$$^-$ was determined. Our results and analysis allowed a near-complete binding-energy-scaled MnO$_4$$^-$$_{(aq.)}$ molecular orbital and a valence energy level diagram to be produced for the MnO$_4$$^-$$_{(aq.)}$ / MnO$_4$$^•$$_{(aq.)}$ system. Cumulatively, our mapping of the aqueous-phase electronic structure of MnO$_4$$^-$ is expected to contribute to a deeper understanding of the exceptional redox properties of this widely applied aqueous transition-metal complex ion., Published by RSC Publ., Cambridge

By use of a combination of electrical measurements and internal photoemission interface barrier characterization, the effective workfunction (EWF) changes of nm-thin TiN layer deposited on top of o...

Cost‐effective and environment‐friendly aqueous zinc‐ion batteries (AZIBs) exhibit tremendous potential for application in grid‐scale energy storage systems but are limited by suitable cathode materials. Hydrated vanadium bronzes have gained significant attention for AZIBs and can be produced with a range of different pre‐intercalated ions, allowing their properties to be optimized. However, gaining a detailed understanding of the energy storage mechanisms within these cathode materials remains a great challenge due to their complex crystallographic frameworks, limiting rational design from the perspective of enhanced Zn2+ diffusion over multiple length scales. Herein, a new class of hydrated porous δ‐Ni0.25V2O5.nH2O nanoribbons for use as an AZIB cathode is reported. The cathode delivers reversibility showing 402 mAh g−1 at 0.2 A g−1 and a capacity retention of 98% over 1200 cycles at 5 A g−1. A detailed investigation using experimental and computational approaches reveal that the host “δ” vanadate lattice has favorable Zn2+ diffusion properties, arising from the atomic‐level structure of the well‐defined lattice channels. Furthermore, the microstructure of the as‐prepared cathodes is examined using multi‐length scale X‐ray computed tomography for the first time in AZIBs and the effective diffusion coefficient is obtained by image‐based modeling, illustrating favorable porosity and satisfactory tortuosity.

Iron phthalocyanines (FePc) adsorbed onto a Ag(110) substrate self-assemble into different monolayer phases going from rectangular to different oblique phases, with increasing molecular density. We have investigated the oxygen uptake capability of the different phases and their associated magneto-structural changes. Our study combines scanning tunneling microscopy and spectroscopy (STM/STS), X-ray magnetic circular dichroism (XMCD), and density functional theory (DFT) calculations. STM measurements reveal that the oxygenation reaction of the FePc/Ag(110) generally involves a displacement and a rotation of the molecules, which affects the electronic state of the Fe centers. The oxygen intercalation between FePc and the substrate is greatly obstructed by the steric hindrance in the high-density phases, to the point that a fraction of oblique phase molecules cannot change their position after oxidizing. Depending on the oxidation state and adsoption geometry, the STS spectra show clear differences in the Fe local density of states, which are mirrored in the XAS and XMCD experiments. Particularly, XMCD spectra of the oxidized phases reflect the distribution of FePc species (nonoxygenated, oxygenated-rotated, and oxygenated-unrotated) in the different cases. Sum rule analysis yields the effective spin (mseff) and orbital (mL) magnetic moments of Fe in the different FePc species. Upon oxygenation, the magnetic moment of FePc molecules increases about an order of magnitude, reaching mTOT ∼ 2.2 μB per Fe atom., We acknowledge financial support from the Spanish MCINN Project (DWARFS MAT2017-83468-R) and the Aragonese Projects E12-17R RASMIA and E09-17R Q-MAD (co-funded by Fondo Social Europeo), and of the European Union FEDER (ES); from the University of Padova Grant CPDA154322 AMNES, and from the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract EFA 194/16 TNSI). M.P. and A.M. are funded by the CERCA Program/Generalitat de Catalunya and the Severo Ochoa program from Spanish MINECO (Grant SEV-2017-0706).

Simulations based on density functional theory (DFT) were used to investigate the behaviour of substitutional iron in both tetragonal and monoclinic ZrO2. Brouwer diagrams of predicted defect concentrations, as a function of oxygen partial pressure, suggest that iron behaves as a p-type dopant in monoclinic ZrO2 while it binds strongly to oxygen vacancies in tetragonal ZrO2. Analysis of defect relaxation volumes suggest that these results should hold true in thermally grown oxides on zirconium, which is under compressive stresses. X-ray absorption near edge structure (XANES) measurements, performed to determine the oxidation state of iron in Zircaloy-4 oxide samples, revealed that 3 + is the favourable oxidation state but with between a third and half of the iron, still in the metallic Fe0 state. The DFT calculations on bulk zirconia agree with the preferred oxidation state of iron if it is a substitutional species but do not predict the presence of metallic iron in the oxide. The implications of these results with respect to the corrosion and hydrogen pick-up of zirconium cladding are discussed.

All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and energy-dispersive X-ray spectroscopy (EDS) data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300°C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500°C by synchrotron X-ray diffraction (XRD). X-ray absorption spectroscopy (XAS) results indicate the presence of also LaCoO3, in addition to La2Zr2O7 and Li2CO3. Based on electrochemical impedance spectroscopy, and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500°C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode-electrolyte interfaces that enable fast Li transfer and high capacity.

Near-infrared emitting persistent phosphors have promising applications in the field of in vivo medical imaging. In this paper, we prepared the persistent phosphor LiGa5O8:Cr3+ (LGO:Cr) which exhibits emission in the tissue transparency window and shows afterglow for multiple hours after excitation. Addition of Si or Ge improves the persistent luminescence. X-ray diffraction and electron microscopy, coupled with elemental analysis, revealed that there is a maximum amount of Si or Ge that can be incorporated in the host. Via X-ray absorption spectroscopy and electron paramagnetic resonance experiments, we studied the local environment of chromium in the LGO spinel host. The presence of both Cr3+ and Cr4+ on octahedral sites in LGO was confirmed. Electron paramagnetic resonance showed that Cr3+ resides in a rhombically distorted octahedral lattice site and that the Cr3+ local environment is sensitive to variation in point defects in the surrounding.

Energy storage solutions are a vital component of the global transition toward renewable energy sources. The power-to-gas (PtG) concept, which stores surplus renewable energy in the form of methane, has therefore become increasingly relevant in recent years. At present, supported Ni nanoparticles are preferred as industrial catalysts for CO2 methanation due to their low cost and high methane selectivity. However, commercial Ni catalysts are not active enough in CO2 methanation to reach the high CO2 conversion (>99%) required by the specifications for injection in the natural gas grid. Herein we demonstrate the promise of promotion of Ni by Mn, another low-cost base metal, for obtaining very active CO2 methanation catalysts, with results comparable to more expensive precious metal-based catalysts. The origin of this improved performance is revealed by a combined approach of nanoscale characterization, mechanistic study, and density functional theory calculations. Nanoscale characterization with scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) and X-ray absorption spectroscopy shows that NiMn catalysts consist of metallic Ni particles decorated by oxidic Mn2+ species. A mechanistic study combining IR spectroscopy of surface adsorbates, transient kinetic analysis with isotopically labeled CO2, density functional theory calculations, and microkinetics simulations ascertains that the MnO clusters enhance CO2 adsorption and facilitate CO2 activation. A macroscale perspective was achieved by simulating the Ni and NiMn catalytic activity in a Sabatier reactor, which revealed that NiMn catalysts have the potential to meet the demanding PtG catalyst performance requirements and can largely replace the need for expensive and scarce noble metal catalysts.

LiMn 2O 4 is a promising candidate for a cathode material in lithium-ion batteries because of its ability to intercalate lithium ions reversibly through its three-dimensional manganese oxide network. One of the promising techniques for depositing LiMn 2O 4 thin-film cathodes is atomic layer deposition (ALD). Because of its unparalleled film thickness control and film conformality, ALD helps to fulfill the industry demands for smaller devices, nanostructured electrodes, and all-solid-state batteries. In this work, the intercalation mechanism of Li + ions into an ALD-grown β-MnO 2 thin film was studied. Samples were prepared by pulsing LiO tBu and H 2O for different cycle numbers onto about 100 nm thick MnO 2 films at 225 °C and characterized with X-ray absorption spectroscopy, X-ray diffraction, X-ray reflectivity, time-of-flight elastic recoil detection analysis, and residual stress measurements. It is proposed that for tBu/H 2O, the Li + ions penetrate only to the surface region of the β-MnO 2 film, and the samples form a mixture of β-MnO 2 and a lithium-deficient nonstoichiometric spinel phase Li xMn 2O 4 (0 < x < 0.5). When the lithium concentration exceeds x ≈ 0.5 in Li xMn 2O 4 (corresponding to 100 cycles of LiO tBu/H 2O), the crystalline phase of manganese oxide changes from the tetragonal pyrolusite to the cubic spinel, which enables the Li + ions to migrate throughout the whole film. Annealing in N 2 at 600 °C after the lithium incorporation seemed to convert the films completely to the pure cubic spinel LiMn 2O 4.

Journal of materials chemistry / A 5(31), 16296 - 16306 (2017). doi:10.1039/C7TA02316B special issue: "Green Materials and Surfaces", Herein, a cost-effective and tailored synthesis route for the preparation of cubic ZrO$_2$ nanocrystals with high dispersibility (up to 45% by weight in H$_2$O) is reported. The procedure is straightforward and produces uniform 2–3 nm particles of a high yield of up to 98% when applying microwave dielectric heating as a “green” method. Furthermore, it can be applied to a wide range of batch sizes (from 0.5 to 20 g ZrO$_2$), which makes it interesting for industrial applications, and also lends itself to the preparation of yttria-stabilized ZrO$_2$ nanocrystals with varying doping levels. Overall, the paper aims at unravelling all relevant reaction steps by means of nuclear magnetic resonance and gas chromatography-mass spectrometry. Two innovative synthesis routes are presented, which have not been considered in previous studies. Both the microstructure and chemical composition of the nanoparticles were analyzed via electron microscopy, X-ray diffraction and dynamic light scattering as well as Raman, X-ray absorption and X-ray photoelectron spectroscopy. Besides, it is demonstrated that alcoholic ZrO$_2$ dispersions are highly suited for the preparation of nanoscale materials with different morphologies, including fibers as well as ordered mesoporous and macroporous thin films and powders. Collectively, this work provides a blueprint for the fabrication of high-quality nanoparticles and structured materials thereof and is likely to trigger further research in the field of solution-processed metal oxides., Published by RSC, London [u.a.]

We report the development of sol-gel derived TiO2 thin films with adjustable and defined properties suitable for memristive cell fabrication. Memristive cells were developed by the sol-gel deposition of titania onto SiO2/Ti/Pt engineered electrodes via spin coating, followed by diverse curing and annealing procedures. The influence of the processing conditions and the sol's chemical composition on the film properties, and therefore on the memristive response, was studied by micro-Raman and transmission spectroscopies, profilometry, ellipsometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray absorption and diffraction spectroscopies (XAS and XRD). A memristive response was acquired from a number of these cells, revealing a dependence of the electrical behavior on minor changes in the TiO2 structure, electroforming parameters, and architecture. Thus, these properties provide a handle for fine-tuning electrical performance.

A series of Li1-xFe1-xVxPO4/C (with 0

International audience; The influence of zirconium as a nucleating agent on the congruent crystallization and relevant physical properties of a supercooled calcium aluminosilicate melt of a composition close to CaAl2SiO6 has been investigated up to 6mol% ZrO2. Zirconium marginally affects rheological and structural properties, decreasing the viscosity of the Zr-free melt by no more than 0.25 log unit and, as observed by Raman spectroscopy, not changing significantly the polymerization state of the material. Whereas the Zr-free melt crystallizes congruently and heterogeneously from the sample surface to yield yoshiokaite, a stuffed derivative of the nepheline structure, addition of zirconia promotes instead bulk crystallization of tetragonal ZrO2 and then of yoshiokaite. The latter process takes place in two stages: dissolved Zr first promotes homogeneous precipitation of zirconia before yoshiokaite crystallizes congruently from a Zr-depleted volume of melt around zirconia precipitates. This process makes zirconium, and probably other poorly soluble oxides, valuable to control congruent crystallization in silicate glass-ceramics. From the recorded thermograms, an enthalpy of crystallization of 40 and 46kJ/mol has been determined at 1060 and 1140K, respectively, for CaAl2SiO6 yoshiokaite, a very low value that is likely due to the extensive atomic disorder of crystals precipitating at high degrees of supercooling

The structure of Ag nanoparticles of different size, supported on the cerium oxide (111) surface, was investigated by X-ray absorption fine structure at the Ag K-edge. The results of the data analysis in the near and extended energy range are interpreted with the help of the results obtained by X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements and allow to obtain a detailed atomic scale description of the model system investigated. The Ag nanoparticles have an average size of a few tens of angstroms, which increases with increasing deposited Ag amount. The nanoparticles show a slight tendency to nucleate at the step edges between different cerium oxide layers and they have a face centered cubic structure with an Ag-Ag interatomic distance contracted by 3-4% with respect to the bulk value. The interatomic distance contraction is mainly ascribed to dimensionality induced effects, while epitaxial effects have a minor role. The presence of Ag-O bonds at the interface between the nanoparticles and the supporting oxide is also detected. The Ag-O interatomic distance decreases with decreasing nanoparticle size.

This manuscript reports the synthesis and characterization of the first organic-inorganic hybrid material exhibiting efficient multimodal spectral converting properties. The nanocomposite, made of Er(3+), Yb(3+) codoped zirconia nanoparticles (NPs) entrapped in a di-ureasil d-U(600) hybrid matrix, is prepared by an easy two-step sol-gel synthesis leading to homogeneous and transparent materials that can be very easily processed as monolith or film. Extensive structural characterization reveals that zirconia nanocrystals of 10-20 nm in size are efficiently dispersed into the hybrid matrix and that the local structure of the di-ureasil is not affected by the presence of the NPs. A significant enhancement in the refractive index of the di-ureasil matrix with the incorporation of the ZrO2 nanocrystals is observed. The optical study demonstrates that luminescent properties of both constituents are perfectly preserved in the final hybrid. Thus, the material displays a white-light photoluminescence from the di-ureasil component upon excitation at UV/visible radiation and also intense green and red emissions from the Er(3+)- and Yb(3+)-doped NPs after NIR excitation. The dynamics of the optical processes were also studied as a function of the lanthanide content and the thickness of the films. Our results indicate that these luminescent hybrids represent a low-cost, environmentally friendly, size-controlled, easily processed and chemically stable alternative material to be used in light harvesting devices such as luminescent solar concentrators, optical fibres and sensors. Furthermore, this synthetic approach can be extended to a wide variety of luminescent NPs entrapped in hybrid matrices, thus leading to multifunctional and versatile materials for efficient tuneable nonlinear optical nanodevices.

The Cu K- and Ce L-3-edge regions have been measured in the hole doped hybrid structured [Nd-2/3(Ce1-xThx)(1/3)](2)-(Ba2/3Nd1/3)(2)Cu3O9-delta (2-2-3), 0 less than or equal to x less than or equal to 1.0, compounds which are superconducting for x less than or equal to 0.30. From the energy positions of the Cu K-edge features, it is clearly noted that 2-2-3 compounds incorporate the K-edge features seen in the oxygen deficient 1-2-3 and the T'-type 2-1-4 superconductors. On progressive Th substitution in 2-2-3, Ce continues to show mixed valence (3(+), 4(+) predominant), Cu remains mainly in 2 + state and no significant change is seen in the weak feature at Cu1+ position. However, noticeable changes in the split white line features at the Cu K-edge are observed. It is inferred from the analysis of the spectral features that a re-distribution of oxygen on the Cu(1) octahedral (defect) site in 2-2-3 occurs with increasing x, affecting adversely the carrier density. This plausibly causes a steep fall in T-c with Th substitution. (C) 1999 .

Ferrimagnetic CoFe2O4 nanopillars embedded in a ferroelectric BaTiO3 matrix are an example for a two-phase magnetoelectrically coupled system. They operate at room temperature and are free of any resource-critical rare-earth element, which makes them interesting for potential applications. Prior studies succeeded in showing strain-mediated coupling between the two subsystems. In particular, the electric properties can be tuned by magnetic fields and the magnetic properties by electric fields. Here we take the analysis of the coupling to a new level utilizing soft X-ray absorption spectroscopy and its associated linear dichroism. We demonstrate that an in-plane magnetic field breaks the tetragonal symmetry of the (1,3)-type CoFe2O4/BaTiO3 structures and discuss it in terms of off-diagonal magnetostrictive-piezoelectric coupling. This coupling creates staggered in-plane components of the electric polarization, which are stable even at magnetic remanence due to hysteretic behaviour of structural changes in the BaTiO3 matrix. The competing mechanisms of clamping and relaxation effects are discussed in detail.

We present and discuss the bremsstrahlung isochromat spectra (BIS) of four d0 transition-metal oxides; namely ZrO2, HfO2, Nb2O5, and Ta2O5. The spectra are related to the density of unoccupied states in the conduction band. They give directly the magnitude of the crystal-field splitting and the dispersion of the metal-d bands. The trends observed in the spectra are discussed and compared to those found in the O 1s x-ray absorption spectra (XAS) of the same materials.

Cataloged from PDF version of article. In this study, we implanted N(+) and N(2)(+) ions into sputter deposited amorphous boron carbide (a-BC) and diamond like carbon (DLC) thin films in an effort to understand the chemical bonding involved and investigate possible phase separation routes in boron carbon nitride (BCN) films. In addition, we investigated the effect of implanted C(+) ions in sputter deposited amorphous boron nitride (a-BN) films. Implanted ion energies for all ion species were set at 40 KeV. Implanted films were then analyzed using x-ray photoelectron spectroscopy (XPS). The changes in the chemical composition and bonding chemistry due to ion-implantation were examined at different depths of the films using sequential ion-beam etching and high resolution XPS analysis cycles. A comparative analysis has been made with the results from sputter deposited BCN films suggesting that implanted nitrogen and carbon atoms behaved very similar to nitrogen and carbon atoms in sputter deposited BCN films. We found that implanted nitrogen atoms would prefer bonding to carbon atoms in the films only if there is no boron atom in the vicinity or after all available boron atoms have been saturated with nitrogen. Implanted carbon atoms also preferred to either bond with available boron atoms or, more likely bonded with other implanted carbon atoms. These results were also supported by ab-initio density functional theory calculations which indicated that carbon-carbon bonds were energetically preferable to carbon-boron and carbon-nitrogen bonds. (C) 2011 American Institute of Physics.

We addressed the issue of bismuth heteroantisite defects (BiGa) in GaAs1-xBix/GaAs epilayers by coupling x-ray absorption spectroscopy at the bismuth edge with density functional theory calculations of the defect structure. Calculations predict a large relaxation of the Bi-As interatomic distances when Bi atoms substitute Ga, however we found no experimental evidence of it. Quantitative analysis of the x-ray absorption spectra allows us to establish a maximum concentration limit for Bi_Ga, which corresponds to about 5% of the total Bi atoms. Bi_Ga do not account for the modifications in the spectra previously attributed to short range ordering.

Titanium oxide nanostructured thin films synthesized by pulsed laser deposition (PLD) were here characterized with a multi-technique approach to investigate the relation between surface electronic, structural and morphological properties. Depending on the growth parameters, these films present characteristic morphologies ranging from compact to columnar and to an extremely open structure. As-deposited films have a disordered structure both in the bulk and on the surface, as shown by Raman spectroscopy and by the fine structure of X-ray absorption spectra near the Ti and O edge (NEXAFS). The surface reactivity towards the atmosphere, with consequent formation of surface hydroxyl terminal groups, turns out to be dependent not only on the effective surface but also on the surface structure. By ultraviolet photoemission spectroscopy, we observed that, depending on the sample structure and morphology, defect states at 1 eV binding energy in the valence band can be induced by exposing the samples to the intense synchrotron photon beam.After annealing in air at 673 K. the structural order increases towards a mainly anatase phase in which the presence of rutile increases in films with a more open morphology. Such structural modifications influence the surface stability since the defect formation in the valence band is strongly reduced in all the annealed films, and it is completely hindered in the most compact films. (C) 2010 Elsevier B.V. All rights reserved.

The atomic level structure of a series of monodisperse single crystalline nanoparticles with a magnetic core of manganese ferrite was studied using X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) techniques at both the Fe and Mn K-edges, and conventional and high resolution transmission electron microscopy (TEM and HRTEM). In particular, insights on the non-stoichiometry and on the inversion degree of manganese ferrite nanocrystals of different size were obtained by the use of complementary structural and spectroscopic characterization techniques. The inversion degree of the ferrite nanocrystals, i.e. the cation distribution between the octahedral and tetrahedral sites in the spinel structure, was found to be much higher (around 0.6) than the literature values reported for bulk stoichiometric manganese ferrite (around 0.2). The high inversion degree of the nanoparticles is ascribed to the partial oxidation of Mn(2+) to Mn(3+) which was evidenced by XANES, leading to non-stoichiometric manganese ferrite.

We investigate the evolution of the Ni electronic and magnetic structure on fs to ps time scales following fs-laser excitation. Within 200 fs after excitation the $\text{Ni}\text{ }3d$ ferromagnetic moment is reduced as probed by x-ray magnetic circular dichroism. At the same time the $\text{Ni}\text{ }3d$ electronic structure undergoes pronounced changes as demonstrated by x-ray absorption spectroscopy. We show that the latter persists also into thermal equilibrium which is reached on the ps time scale. Cluster calculations identify a reduction in $3d\ensuremath{-}4sp$ hybridization possibly associated with phonon-driven spin-flip excitations.

In this work, we developed and optimised a synthetic route which enables to produce by spray-coating hard, transparent and stable inorganic–organic hybrid coatings for a wide variety of different substrates (e.g. stone, stainless steel, polymethylmethacrylate, polyethylene, wood, anodized aluminum). Chemically and thermally stable acrylate-based hybrid materials embedding the zirconium oxocluster Zr4O2(OMc)12, OMc (CH2 C(CH3)C(O)O) were prepared and UV-cured. The coatings of different compositions on different substrates were characterized by numerous analytical and spectroscopic methods such as FT-IR spectroscopy, Angle Resolved-XPS (AR-XPS), Secondary Ion Mass Spectrometry (SIMS), X-ray Absorption Spectroscopy (XAS), Environmental Scanning Electron Microscopy (ESEM) and Energy Dispersive X-ray analysis (EDX). Bulk samples were also prepared for additional characterizations. The bulk samples were analysed by FT-IR, whereas the cross-linking degree was qualitatively evaluated by swelling experiments. As far as the mechanical properties are concerned, the shear storage modulus (G′) and loss modulus (G″) were measured by Dynamical Mechanical Thermal Analysis (DMTA) technique. Moreover, the best conditions for the curing and cross-linking processes of the hybrid materials were studied up to 200 °C by using Differential Scanning Calorimetry (DSC). The thermal stability of the hybrid samples was evaluated by Thermogravimetric Analysis (TGA).

We exploited complementary synchrotron radiation spectroscopies to study the Yb 4f electronic configuration in three representative intermediate-valence materials: YbAl3, YbInCu4, and YbCu2Si2. High-resolution x-ray absorption (PFY-XAS), resonant inelastic x-ray scattering (RIXS), and hard-x-ray photoemission (HAXPES) data all show characteristic temperature-dependent changes of the Yb valence. For each material, the increments measured from low (20 K) to high (300 K) temperature by the different probes are quite similar. The estimated RIXS and XAS valences are consistently higher than the HAXPES values. We briefly discuss the possible origin of this discrepancy.

We report a detailed investigation of interdiffusion processes that occur during the growth of germanium nanostructures on the (111)-oriented surface of silicon. In particular, X-ray Absorption Fine Structure (XAFS) measurements performed ex situ show that a Ge(1-x)Si(x) alloy forms during deposition, with average composition x varying between 0.25 and 0.50, depending on substrate temperature and total coverage. By fitting the Si nearest-neighbor numbers around Ge as a function of the deposited thickness with a simple model, the effective vertical composition profile in the growth direction has been estimated. The latter has been described with a static effective diffusion length of (10.0 +/- 1.5) nm at 530 degrees C and (5 +/- 1) nm at 450 degrees C, which is interpreted as the dominance of surface transport processes in the intermixing dynamics. The analysis of the data on Ge-Ge bond length indicates a decrease of the Ge-Ge atomic distances with increasing Ge fraction, confirming previous theoretical predictions for strained epilayers. The XAFS results are compared to morphological information obtained by scanning tunneling microscopy investigations carried out in situ, yielding a satisfactory description for the epitaxy of this system.

A comparative study of Li1-xMn2-xO4 (0

We present a systematic study of the perovskite-related system La2-xSrxCu1-yRuyO4 using Cu-L2,3, Ru-L2,3, and O-K x-ray absorption spectroscopy (XAS). This system can be regarded as a solid solution of the two superconductors La2-xSrxCuO4 and Sr2RuO4, and thus the question as to the destination of the holes induced by Sr doping is central to our understanding of these novel systems. The comparison of the experimental data with state-of-the-art crystal-field-multiplet calculations shows clearly that the charge balance for x/2y >1 is predominantly achieved by an increase of the Ru valence from Ru(IV) to Ru(V), while Cu remains in the Cu(II) oxidation state., Text = 1 .pdf file. Figs (all) = 1 .pdf file. Submitted to PRB

By using a transmission-electron microscope, we have performed electron-energy loss measurements above the O K-edge at ≈ 528 eV on very thin layers cut from good-quality single crystals of Bi 2- x Pb x Sr 2 CaCu 2 O 8 . We have selected a surface reg ion of the superconductor of known chemical composition free from microprecipitates of Ca. For different directions of the transfer momentum q with respect to the c -axis we observe for the first time the strong orientational dependence of the O K-edge transitions in the extended energy loss fine structure. The momentum-transfer-resolved radial distribution functions allow one to identify several characteristics bond lengths of O-Cu and O-Bi parallel and perpendicular to the c -axis.

We predict very strong peak enhancements in core-level photoemission at the resonance with a deeper core-level absorption. This allows a straightforward interpretation of core-level spectroscopy in two ways: (a) photoemission peaks can be resolved in resonance with different x-ray absorption peaks, and (b) x-ray absorption peaks can be resolved using partial electron yield at constant binding energy. This can be used to study covalency effects in transition-metal, rare-earth, and actinide compounds. An example is given for nickel metal using a cluster calculation including multiplet structure.

By combining HERFD-XAS at the uranium L 1-, L 3- and M 4-edge with relativistic quantum chemistry calculations the uranium valence electronic structure in KUO3 could be assessed in detail. The contribution of uranium and oxygen states in observed spectral features is discussed., The uranium valence electronic structure in the prototypical undistorted perovskite KUO3 is reported on the basis of a comprehensive experimental study using multi-edge HERFD-XAS and relativistic quantum chemistry calculations based on density functional theory. Very good agreement is obtained between theory and experiments, including the confirmation of previously reported Laporte forbidden f–f transitions and X-ray photoelectron spectroscopic measurements. Many spectral features are clearly identified in the probed U-f, U-p and U-d states and the contribution of the O-p states in those features could be assessed. The octahedral crystal field strength, 10Dq, was found to be 6.6 (1.5) eV and 6.9 (4) eV from experiment and calculations, respectively. Calculated electron binding energies down to U-4f states are also reported.

Uranium (U) is a ubiquitous element in the Earth’s crust at ~2 ppm. In anoxic environments, soluble hexavalent uranium (U(VI)) is reduced and immobilized. The underlying reduction mechanism is unknown but likely of critical importance to explain the geochemical behavior of U. Here, we tackle the mechanism of reduction of U(VI) by the mixed-valence iron oxide, magnetite. Through high-end spectroscopic and microscopic tools, we demonstrate that the reduction proceeds first through surface-associated U(VI) to form pentavalent U, U(V). U(V) persists on the surface of magnetite and is further reduced to tetravalent UO2 as nanocrystals (~1–2 nm) with random orientations inside nanowires. Through nanoparticle re-orientation and coalescence, the nanowires collapse into ordered UO2 nanoclusters. This work provides evidence for a transient U nanowire structure that may have implications for uranium isotope fractionation as well as for the molecular-scale understanding of nuclear waste temporal evolution and the reductive remediation of uranium contamination. In anoxic environments, soluble hexavalent uranium is reduced and immobilized, however, the underlying molecular-scale reduction mechanism remains unknown. Here, the authors find that U reduction can occur on the surface of magnetite via transient U nanowire structures which collapse into ordered UO2 nanoclusters, which may have implications for understanding nuclear waste evolution and remediation of uranium contamination.

Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments have been carried out on GaAsO4 (berlinite structure) at high pressure and room temperature. XAS measurements indicate four-fold to six-fold coordination changes for both cations. The two local coordination transformations occur at different rates but appear to be coupled. A reversible transition to a high pressure crystalline form occurs around 8 GPa. At a pressure of about 12 GPa, the system mainly consists of octahedral gallium atoms and a mixture of arsenic in four-fold and six-fold coordinations. A second transition to a highly disordered material with both cations in six-fold coordination occurs at higher pressures and is irreversible., 8 pages, 5 figures, LaTeX2e

By means of Mn-Cu transmetalation, we incorporated Mn atoms in an array of TCNQ (7,7,8,8-tetracyanoquinodimethane) grown on Cu(100), forming a long range ordered and commensurate metal–organic coordination network (MOCN). Preliminary Sn alloying of the Cu(100) surface allowed us to control the degree of substrate reactivity, thus preventing the chemical interaction of the Mn-TCNQ MOCN with the substrate. Mn 2 + ions are stabilized in an artificial tetra-pyrrolic coordination, which mimics the macrocyle configuration of Mn-phthalocyanines/porphyrins. X-ray absorption spectroscopy at the Mn L 2 , 3 -edge indicates that the Mn ions are in a high-spin state (S = 5/2), in agreement with DFT + U calculations which also shows that the electronic structure of this Mn-TCNQ MOCN is very similar to that of the corresponding unsupported MOCN.

In the landscape of ultrafast spectroscopic tools, the deep- and near-ultraviolet ranges (200-400 nm) have lagged behind due to the lack of tunability of both the pump and the probe pulses in this range. With the advent of novel nonlinear optical methods, this has now become possible. In this perspective, I will review some of the recent studies in the 250-400 nm range on (bio)chemical systems in order to stress the capabilities of ultrafast deep-UV spectroscopy to unravel new phenomena. This will serve as a basis to dwell on the promise and the new directions not only for molecular systems but also materials in solid or nanostructured form.