X-Ray Absorption Spectroscopy (in Materials Characterisation/X Ray Analysis) Research Papers (original) (raw)

Thangkas are scroll Tibetan Buddhist paintings on cotton or silk, usually
depicting a Buddhist deity. The monastery collection counts unique pieces as 12th century Kashmiri thangkas, which deserved to be analysed. A total of 28 thangkas have been analysed: for the most precious ones, all the colours have been characterized (traces and main elements) and for the others only the white pigments and preparation were investigated. Preparation and white pigments are found locally
and can thus help to define provenance. Different clays with or without gypsum have been used and several groups of thangkas can be defined according to it.

The Tunisian industrial phosphoric acid (IPA) was obtained from the phosphate rock by the wet process. However, the organic matter (OM) contained in the acid may interact with organic solvents to form stable foams, preventing phase settling, or simply by forming cross layers and organic phases, and denaturing part of the solvent. Hence, removal of these organics seems to be an important step for the production of decontaminated phosphoric acid. In the phosphoric acid plant of M'dhilla, the OM can be found as colloidal suspension and soluble forms. The colloidal organics are coagulated and deposited with the gypsum precipitation during the aging of H 3 PO 4 , while the soluble part remains behind. The purpose of this work was to study the OM adsorption onto montmorillonite bentonite. Equilibrium data are analyzed by the Langmuir, Freundlich and Redlich–Peterson adsorption isotherm models. ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

A collection of window-panes, vessels and alleged waste from Thamusida has been investigated by OM, SEM–EDS, ICP–MS, ICP–OES and XAS at the Fe–K and Mn–K edges. Glass samples have been characterized as natron-based soda–lime–silica glasses, with low magnesium and low potassium. The results have been compared with 43 reference groups available for ‘naturally coloured’ and colourless glasses of both Roman and later ages. Two main types were distinguished: RBGY 1 (Roman Blue–Green and Yellow 1) and RBGY 2 (Roman Blue–Green and Yellow 2). Given their compositional similarity to the Levantine I or, to a lesser extent, HIMT glasses, the Syrian–Palestinian coast for RBGY 2 and Egypt for the RBGY 1 have been suggested for their provenance. Most Thamusida samples have been assigned to the RBGY 2 type. A small group of Thamusida colourless vessels was included into the RC (Roman-Colourless) compositional field; the latter still being defined. The alleged waste pieces may define a local production that should have been of secondary type. The investigations performed on local raw materials seem to discount the possibility of a primary glass-making site. XAS measurements determined that Fe2+ contents ranging between 30 and 52% are able to assure an aqua blue colour; below 30%, the glasses turn light green or light yellow.

- by Elisabetta Gliozzo
- •
- Archaeology, Classical Archaeology, Colour Science, Archaeological Science

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxial quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank-van der Merve to Stranski-Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1-x-yGexCy material, as determined by Vegard's law, and the equilibrium Si-C bond length, weakens the Si-C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1-x-yGexCy films with increasing C incorporation suggests a repulsive Ge-C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 degrees C, whereas at 450 degrees C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. (

We report the results of the studies on crystal structure, electronic structure and dielectric properties of Er 1-x La x FeO 3 (ELFO) (x ¼ 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) orthoferrites synthesized by co-precipitation method. Rietveld refinement of the XRD data confirms the orthorhombic crystal structure for all the samples. The study of Fe L 3,2-edge X-ray Absorption spectroscopy shows the presence of Fe-ions in 3 þ valence state in all the samples. Investigations on the dielectric behavior of ELFO samples over the wide frequency range of 20 Hz to 5 MHz show the increment in the dielectric constant with La-doping. ErFeO 3 has the lowest value of dielectric constant whereas LaFeO 3 has the highest value of dielectric constant among all the samples. Effect of grain and grain boundary contribution on the dielectric behavior is studied using complex dielectric permittivity. The observed colossal dielectric behavior in LaFeO 3 is attributed to the combined contribution from the intrinsic dielectric constant of the material and that due to the modification in the microstructure.

SEM–EDS, EMPA, ICP–MS and ICP–OES were applied to the study of three sectilia panels made of red, orange and yellow glass slabs. In order to determine the chemical state of Cu, XAS was also performed. The results indicate that, with the exception of the red samples, all slabs were made by mixing a siliceous sand with natron. The red slabs show significant compositional differences with respect to K2O and MgO contents, probably linked to the use of plant ashes as a source of alkali. The red, orange and yellow slabs are coloured by metallic copper, cuprite and Pb antimonates, respectively. The comparison between the chemical composition of the Faragola samples and several glass reference groups did not provide conclusive evidence of provenance.

The influence of the organic content, sample preparation process and the morphology of the depositions of two types of Coke beverage, traditional and light Coke, have been investigated by mean of Total-reflection X-ray Fluorescence (TXRF) spectrometry. Strong distortions of the nominal concentration values, up to 128% for P, have been detected in the analysis of traditional Coke by different preparation methods. These differences have been correlated with the edge X-ray energies of the elements analyzed being more pronounced for the lighter elements. The influence of the organic content (mainly sugar) was evaluated comparing traditional and light Coke analytical TXRF results. Three sample preparation methods have been evaluated as follows: direct TXRF analysis of the sample only adding internal standard, TXRF analysis after open vessel acid digestion and TXRF analysis after high pressure and temperature microwave-assisted acid digestion. Strong correlations were detected between quantitative results, methods of preparation and energies of the X-ray absorption edges of quantified elements. In this way, a decay behavior for the concentration differences between preparation methods and the energies of the X-ray absorption edges of each element were observed. The observed behaviors were modeled with exponential decay functions obtaining R 2 correlation coefficients from 0.989 to 0.992. The strong absorption effect observed, and even possible matrix effect, can be explained by the inherent high organic content of the evaluated samples and also by the morphology and average thickness of the TXRF depositions observed. As main conclusion of this work, the analysis of light elements in samples with high organic content by TXRF, i.e. medical, biological, food or any other organic matrixes should be taken carefully. In any case, the direct analysis is not recommended and a previous microwave-assisted acid digestion, or similar, is mandatory, for the correct elemental quantification by TXRF.

Iron spectra have been recorded from plasmas created at three different laser plasma facilities: the Tor Vergata University laser in Rome (Italy), the Hercules laser at ENEA in Frascati (Italy), and the Compact Multipulse Terawatt (COMET) laser at LLNL in California (USA). The measurements provide a means of identifying dielectronic satellite lines from Fe xvi and Fe xv in the vicinity of the strong 2p ! 3d transitions of Fe xvii. About 80n 1 lines of Fe xv (Mg-like) to Fe xix (O-like) were recorded between 13.8 and 17.1 8 with a high spectral resolution (k/k 4000); about 30 of these lines are from Fe xvi and Fe xv. The laser-produced plasmas had electron temperatures between 100 and 500 eV and electron densities between 10^20 and 10^22 cm3. The Hebrew University Lawrence Livermore Atomic Code (HULLAC) was used to calculate the atomic structure and atomic rates for Fe xv–xix. HULLAC was used to calculate synthetic line intensities at Te ¼ 200 eV and ne ¼ 1021 cm3 for three different conditions to illustrate the role of opacity: optically thin plasmas with no excitation-autoionization/dielectronic recombination (EA/DR) contributions to the line intensities, optically thin plasmas that included EA/DR contributions to the line intensities, and optically thick plasmas (optical depth 200 m) that included EA/DR contributions to the line intensities. The optically thick simulation best reproduced the recorded spectrum from the Hercules laser. However, some discrepancies between the modeling and the recorded spectra remain.

Resonant inelastic scattering measurements of the conjugated polymer, poly (pyridine-2, 5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules.

Analyses at the Cu–K, Fe–K and Mn–K edge were performed to study the green, marbled (green and yellow), blue and blackish (deep greyish olive green) glass slabs decorating three sectilia panels from the archaeological site of Faragola. Results indicate that all slabs were made by mixing siliceous sand with natron, sometimes probably mixed with small percentages of plant ash. Cu2+ and Pb antimonates should be responsible for the opaque green colours. The dark green and yellow portions of the marbled slabs are respectively comparable to the slabs comprising only one of these colours. Cu2+ together with Ca antimonates probably produced light blue slabs, whereas cobalt was used to produce dark blue slabs. We consider it possible that the abundance ratio of Fe2+/Fe3+ and the complex Fe3+S2− would have an effect on the blackish slabs. The contribution of Mn cannot be ascertained even if it could have played a role in darkening glass colour. The comparison between the chemical composition of Faragola samples and several glass reference groups provided no conclusive evidence of provenance; whereas, the presence of a secondary local workshop can be hypothesized.

- by Elisabetta Gliozzo and +2
- •
- Late Antique and Byzantine Studies, Colour Science, Archaeological Science, Late Antique Archaeology

Highly c-axis-oriented Zn1-xMgxO multilayered thin films have been deposited on p-type Si
substrates with different concentration of Mg (x = 0.00−0.40) using a sol–gel spin-coating
technique. The x-ray diffraction (XRD) shows that single-phase wurtzite thin films start
showing phase segregation for a Mg content of x = 0.25 for the sol–gel-derived ZnMgO thin
films. The element specific near edge x-ray fine structure (NEXAFS) collected at O K-edge
also clearly evidence the phase segregation at x = 0.25. These results also show that films are
deposited with wurtzite structure as dominant phase even after phase segregation. The
NEXAFS spectra collected at Zn L3-edge rule out the presence of any Zn-related defect due to
Mg doping. The atomic force microscopy (AFM) depicts the spherical shape of nanosized
grains, and grain size varies slightly with Mg content. The single-phase ZnMgO thin films
show a band gap tuning from 3.38 to 3.84 eV, which is also consistent with blue shifting of
near-band edge PL emission. The electrical resistivity of thin films increases with Mg content
before phase segregation. However, the optical band gap, photoluminescence and electrical
resistivity show anomalous behavior at phase segregation limit which has been discussed and
correlated with each other.

Mn dissolution is the main drawback of LiMn 2 O 4 cathodes, leading to capacity fading and anode poisoning. It is well known that improved capacity/cycling performances have been obtained by the Al 2 O 3 coating. It is less clear what is the effect of the coating from the point of view of the fundamental processes occurring within the active material and on the interface with the active material, especially during the first cycle, when a dynamical interaction at a high voltage with an electrolyte and a binder leads to the formation of a passivation layer. We present here the close comparison of coated and uncoated electrodes' X-ray absorption analysis at the interface during the measurements of several charged/discharged states of the electrode. The Al 2 O 3 coating is significantly effective for stopping the high voltage instability of the battery, especially, when the Mn−O couple reacts with organic species, limiting Mn capture and the electrolyte reaction with the oxide surface. In the low-voltage discharge, on the other hand, more complex structure/electronic modifications occur. The presence of the coating limits disproportionation, preventing a general corrosion with dissolution of the Mn 2+ species, and hence improves the electrode performance. From the structural point of view, the signatures of the transformations and a reversible modification of the surface character of the nanoparticles from a spinel to a defective phase are observed, while no charge transfer between the coating and manganese oxide is found. The role of nonthermodynamic interphase formation by means of proton transfer is enhanced for the coated oxide particles.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract The environmental troubles that are related to cement manufacturing makes the new studies moving forward to using materials have less environmental impact, thus, in this paper we utilized different type of recycled glass such as (neon glass, brown glass, and green glass) that has high percentage of silicon dioxide (SiO2) with different concentrations. Utilization these landfall materials can be considered as keeping on resources. Different waste glasses used as a partial replacement of cement with different concentrations 11%, 13%, and 15% of cement weight for each type, and study the effect of it on the mechanical properties of concrete. After mixing, casting, and curing in water at (20±2)°C for (7, 14, and 28) days, the mechanical properties showed that the compressive strength and flexural show highest results at 13% from cement weight of neon glass, whereas splitting tensile strength appeared the highest value at the same percentage but from green glass.

We demonstrate the effect of inversion population ratio mediated by 980 nm pumping band on the gain spectra of a gain-flattened Erbium-doped fiber amplifier. The gain equalizing filter was designed at 977 nm and the amplifier was built in the four-stage arrangement. In the pumping structure, the 1480 nm lasers were maintained in the final gain block while the 980 nm band lasers were utilized in the first three blocks. These laser sources were arranged at several combinations of 977 and 980 nm wavelengths. Within these 3 nm spectrum, an absorption cross-section difference around 0.32 × 10-25 m2 contributed to a dispensable gain variation up to 3-dB. These inequalities were the results of variations in population inversion induced by the pump wavelength discrepancy. The findings show the importance of designing a filter at the specific absorption wavelength to allow the operation of consistent gain level.

XAFS (X-ray absorption fine structure) spectra were measured by using the fluorescence spectrometer for the emitted X-ray from sample. The chemical shifts between Cu 0 and Cu I and between Cr III and Cr VI were evaluated. Tuning the fluorescence spectrometer to each energy, the Cu 0 and Cu I site-selective XANES for Cu/ZnO catalyst were measured. The first one was similar to the XANES of Cu metal and the second one was the 5 : 5 average of XANES for Cu I sites + Cu metal. The population ratio of copper site of the Cu/ZnO catalyst was found to be Cu metal : Cu 2 O : Cu I atomically dispersed on surface = 70(±23) : 22(±14) : 8(±5). Site-selective XANES for Cr III site of Cr/SiO 2 catalyst was also studied.

The physicochemical state of a catalyst is a key factor in determining both activity and selectivity; however these materials are often not structurally or compositionally homogeneous. Here we report on the 3-dimensional imaging of an industrial catalyst, Mo-promoted colloidal Pt supported on carbon. The distribution of both the active Pt species and Mo promoter have been mapped over a single particle of catalyst using microfocus X-ray fluorescence computed tomography. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure revealed a mixed local coordination environment, including the presence of both metallic Pt clusters and Pt chloride species, but also no direct interaction between the catalyst and Mo promoter. We also report on the benefits of scanning μ-XANES computed tomography for chemical imaging, allowing for 2- and 3-dimensional mapping of the local electronic and geometric environment, in this instance for both the Pt catalyst and Mo promoter throughout the catalyst particle.

The structural analysis of LaCo1xNixO3 (0x0.5) samples assures single phase rhombohedral
structure with space-group R3 c. Electronic structure of these samples has been studied by x-ray
absorption near edge spectroscopy (XANES) at K-edge of O, Ni, Co and M5,4 edge of La. These
studies confirm the trivalent state of Co/Ni and La in all the compositions. Upon substitution of the
Ni at the Co site in LaCoO3, the O K-edge spectra show a feature about 1.2 eV lower than that of
LaCoO3. This feature keeps on growing as the concentration of the Ni is increasing. This is
consistent with our resistivity data which shows drastic decrease in resistivity with the Ni
substitution. The resistivity data have been analyzed using Arrhenius and Efros-Shklovski’s type
variable range hopping models in different temperature ranges. The activation energy decreases
and localization length increases systematically with increase in the Ni concentration. Observed
features have been explained on the basis of change in charge-carrier density with substitution. The
disorder-induced localization of carriers is found to govern conduction mechanism and resistivity
behavior in substituted sample.

Abstract: The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant X-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant X-ray emission spectra show depletion of the {\ pi} electron bands due to the selective excitation which enhances the effect of symmetry selection rules.

XTACH 2011, an international conference on the use of X-ray (and related) techniques in arts and cultural heritage was held on 7th-8th December 2012 at the American University of Sharjah in the United Arab Emirates (UAE). The conference was organized in cooperation with the National X-ray Fluorescence Laboratory (NXFL) and the International Atomic Energy Agency (IAEA). The conference was inaugurated by Dr. Peter Heath, Chancellor of the American University of Sharjah and attended by Mr. Kwaku Aning, Deputy Director General of the International Atomic Energy Agency (IAEA), and Ambassador Hamad Al-Kaabi, Ambassador of the UAE to the IAEA, university officials, faculty members and students. The conference covered a variety of topics including the usage of X-ray and micro beam X-ray analysis, synchrotron based techniques, ion beam and neutron based techniques, optical imaging and mass spectroscopy, chromatography techniques, as well as best conservation practices.

For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using microsecond time-resolved X-ray absorption spectroscopy at the Ti K-edge in order to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just below the main edge increase with an increase in the amplitude of the applied electric field, whereas that of the main peak decreases in an opposite manner. Based on the multiple scattering theory, the increase and decrease of the eg and main peaks are simulated for different Ti off-center displacements. Our results indicate that these spectral features reflect the inter- and intra- atomic hybridization of Ti 3d with O 2p and Ti 4p, respectively. In contrast, the shoulder structure is not affected by changes in the Ti off-center displacement but is susceptible to the effect of the corner site Ba ions. This is the first experimental verification of electronic contribution of Ba to polarization reversal.

The electronic structure, chemical bonding, and interface component in ZrN-AlN nanocomposites formed by phase separation during thin film deposition of metastable Zr 1−x Al x N (x = 0.0, 0.12, 0.26, 0.40) are investigated by resonant inelastic x-ray scattering, x-ray emission, and x-ray absorption spectroscopy and compared to first principles calculations including transitions between orbital angular momentum final states. The experimental spectra are compared with different interface-slab model systems using first principles all-electron full-potential calculations where the core states are treated fully relativistically. As shown in this work, the bulk sensitivity and element selectivity of x-ray spectroscopy enables one to probe the symmetry and orbital directions at interfaces between cubic and hexagonal crystals. We show how the electronic structure develops from local octahedral bond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results in three different kinds of bonding originating from semicoherent interfaces with segregated ZrN and lamellar AlN nanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes place with increasing Al content and affects the bond strength and increases resistivity.

The electronic structure and chemical bonding of -Ta synthesized as a thin 001-oriented film (space group P¯421m) is investigated by 4f core level and valence band X-ray photoelectron spectroscopy and compared to -Ta bulk. For the -phase, the 4f7/2 peak is located at 21.91 eV and with the 4f5/2 at 23.81 eV which is 0.16 eV higher compared to the corresponding 4f peaks of the -Ta reference. We suggest that this chemical shift originates from electron screening, higher resistivity or strain in the -Ta film. Furthermore, the 5d-5s states at the bottom of the valence band are shifted by 0.75 eV towards higher binding energy in -Ta compared to -Ta. This is a consequence of the lower number of nearest neighbors with four in -Ta compared to eight in the -Ta phase. The difference in the electronic structures, spectral line shapes of the valence band and the energy positions of the Ta 4f, 5p core-levels of -Ta versus -Ta are discussed in relation to calculated states of -Ta and -Ta. In particular, the lower number of states at the Fermi level of -Ta (0.557 states/eV/atom) versus -Ta (1.032 states/eV/atom) that according to Mott’s law should decrease the conductivity in metals and affect the stability by charge redistribution in the valence band. This is experimentally supported from resistivity measurements of the film yielding a value of ~170  cm in comparison to -Ta bulk with a reported value of ~13.1  cm.

Investigations of chemical bonding and electronic structure features for polycrystalline (porphyrinato)nickel (II) (NiP, the simplest Ni porphyrin), (5,10,15,20-tetraphenylporphyrinato)nickel (II) (NiTPP) and (2-aza-21-carba-5,10,15,20-tetraphenylporphyrinato)nickel (II) (N-confused NiTPP, NiNCTPP) have been performed by means of high-resolution soft x-ray absorption and x-ray photoemission spectroscopy. The Ni 2p 3/2 x-ray absorption spectra show strong π-back-bonding in these compounds leading to a high-energy shift (1.2 eV for the NiP and NiTPP) of the entire absorption structure compared to Ni metal. It has been found that the main absorption line of the Ni 2p 3/2 spectrum of the NiNCTPP is shifted by an additional 0.5 eV to higher energies in comparison with those for other nickel porphyrins. This shift is evidence of stronger back-donation (metal-to-ligand charge transfer) and a smaller effective number of 3d electrons on the central Ni atom in the NiNCTPP as compared to other Ni porphyrins. The confused N atom in the NiNCTPP is of pyrrolic type (protonated nitrogen), which was confirmed by the N 1s absorption and core-level photoemission spectra.

"ZrO2 thin films were deposited on Si (100) substrates using pulsed laser deposition. Swift heavy ion irradiation
experiments, with different ion fluence, were performed using 200 MeV Ag-ion beam. X-ray diffraction,
Raman spectroscopy and O K – edge X-ray absorption spectroscopy measurements confirmed
the dissolution of monoclinic phase and fruition of tetragonal phase of ZrO2 with the increase of ion fluence.
The mechanism of such structural evolutions is briefly discussed in light of ion-irradiation induced
local temperature rising, overlapping of latent tracks and energy loss processes"

Results are presented from X-ray absorption spectroscopy based analysis of As, Cr and V speciation within samples of bauxite ore processing residue (red mud) collected from the spill site at Ajka, Western Hungary. Cr K-edge XANES analysis found that Cr is present as Cr3+ substituted into hematite, consistent with TEM analysis. V K-edge XANES spectra have E½ position and pre-edge features consistent with the presence of V5+ species, possibly associated with Ca-aluminosilicate phases. As K-edge XANES spectra identified As present as As5+. EXAFS analysis reveals arsenate phases in red mud samples. When alkaline leachate from the spill site is neutralised with HCl, 94 % As and 71 % V is removed from solution during the formation of amorphous Al-oxyhydroxide. EXAFS analysis of As in this precipitate reveals the presence of arsenate Al-oxyhydroxide surface complexes. These results suggest that in the circumneutral pH, oxic conditions found in the Torna and Upper Marcal catchments, incorporation and sorption respectively will restrict the environmental mobility of Cr and As. V is inefficiently removed from solution by neutralisation, therefore, the red mud may act as a source of mobile V5+ where the red mud deposits are not removed from affected land.

- by William Mayes
- •
- Water, Environmental Geology, Disaster Studies, Water quality

Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method's impressive electronic structure sensitivity for excited-state investigations.

The Cu 2p, I 3d, and C 1s X-ray absorption spectra of the CuI@SWCNT nanocomposite prepared
by filling single-walled carbon nanotubes (SWCNTs) with the CuI melt by the capillary technique have been
measured with a high-energy resolution using the equipment of the Russian–German beamline at the
BESSY electron storage ring. In order to characterize the electronic structure of the nanocomposite and possible changes in the atomic and electronic structures of CuI and SWCNTs in the CuI@SWCNT nanocomposite, the spectra obtained have been analyzed in the framework of the quasi-molecular approach by comparing with the spectra of the pristine (CuI and SWCNT) and reference (CuO) systems. It has been revealed that the encapsulation of the CuI compound inside SWCNTs is accompanied by changes in the electronic
structure of CuI and SWCNTs due to the chemical interaction between the filler and carbon nanotubes and the change in the atomic structure of CuI.

NiX2@SWCNT (X¼Cl, Br) nanostructures were prepared by
capillary filling of single-walled carbon nanotube channels with nickel halogenide melts with slow cooling down to room
temperature for better crystallization. The HRTEM data indicated formation of well-ordered 1D NiBr2 crystals, with the experimental atomic structure representing a fragment of the bulk structure. The lattice constant coincides with the corresponding distance in bulk lattice. The 1D crystal structure was modeled using DFT within the PW-GGA approach. According to the Raman, X-ray photoelectron, X-ray and optical absorption spectroscopic data and the DFT results obtained within the rigid band model, nickel halogenides display acceptor behavior with the corresponding charge transfer from the single-walled carbon
nanotube walls to the NiX2 nanocrystals.

- by Nicole Herbots
- •
- Optical Engineering, Physics, Condensed Matter Physics, Solid State Physics

Recently, the interest in nanolaminated ternary Mn+ 1AXn denoted 211, 312, and 413, where n= 1, 2, and 3, respectively carbides and nitrides, so-called MAX phases, has grown significantly. Here, M is an early transition metal, A is ap... more

Strontium titanate is a model quantum paraelectric in which in the region of dominating quantum statistics the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero-point motion contribution. The enhancement of atomic masses by the substitution of 18 O for 16 O decreases the zero-point atomic motion and low-T ferroelectricity in SrTi 18 O 3 is realized. In this study we report on the local structure of Ti in SrTi 16 O 3 and SrTi 18 O 3 by Ti K-edge extended x-ray absorption fine structure measurements in temperature range 6-300 K.

The processes by which Athenian black- and red-figure vases were produced appear to be well understood, with text-books regularly offering succinct descriptions of levigation, the application of relief line, and the three-stage firing process. A number of aspects, however, remain hypothetical, and new analytical techniques can inform old questions. In 2011, with funding from the National Science Foundation, the Getty Conservation Institute and J. Paul Getty Museum undertook a project to characterize Athenian black gloss. By partnering with The Aerospace Corporation, the Stanford Synchrotron Radiation Lightsource (SSRL), and The Northwestern University/Art Institute of Chicago Center for Scientific Studies in the Arts (NU-ACCESS), we created a team which had a diverse range of interests and equipment, with a view to obtaining new and rigorously-tested data. Combining these analyses with replication studies, we documented the ways in which black gloss responded during firing. Some of the results have been published in scientific journals, but in order to share them more broadly, we present here a summary of three case-studies. Taken together, they indicate that the production of the vases may be more complex than
the conventional notion of a single three-stage firing process (oxidation-reduction-oxidation) suggests.

Pure spin currents have potential for use in energy-friendly spintronics. They can be generated by a flow of charge along a nonmagnetic metal with large spin−orbit coupling. This produces a spin accumulation at the surfaces, controllable by the magnetization of an adjacent ferromagnetic layer. Paramagnetic metals typically used are close to ferromagnetic instability and thus magnetic proximity effects can contribute to the observed angular-dependent magnetoresistance (ADMR). As interface phenomena govern the spin conductance across the metal/ferromagnetic−insulator heterostructures, unraveling these distinct contributions is pivotal for a full understanding of spin current conductance. Here, we report X-ray absorption and magnetic circular dichroism (XMCD) at Pt M and (Co, Fe) L absorption edges and atomically resolved energy electron loss spectroscopy (EELS) data of Pt/CoFe 2 O 4 bilayers, where CoFe 2 O 4 layers have been capped by Pt grown at different temperatures. It was found that the ADMR differs dramatically, dominated either by spin Hall magnetoresistance (SMR) associated with the spin Hall effect or by anisotropic magnetoresistance. The XMCD and EELS data indicate that the Pt layer grown at room temperature does not display any magnetic moment, whereas when grown at a higher temperature, it becomes magnetic due to interfacial Pt-(Co, Fe) alloying. These results enable differentiation of spin accumulation from interfacial chemical reconstructions and tailoring of the angular-dependent magnetoresistance.

The local electronic and atomic structures of the high-quality single crystal of SrFeO3-δ (δ~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L3,2-edge X-ray linear dichrois results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d eg states remain in persistently out-of-plane 3d3z2-r2 orbitals. In contrast, in the warming process below the transition temperature, they change from 3d3z2-r2 to in-plane 3dx2-y2 orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3dx2-y2 and out-of-plane 3d3z2-r2 orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-δ (δ~ 0.19) single crystal.

Investigations of chemical bonding and electronic structure features for polycrystalline Ni(II) phthalocyanine (NiPc), Ni(II) tetra-benzoporphyrin (NiTBP), Ni(II) 2,3,7,8,12,13,17,18-octaethylporphyrin (NiOEP), Ni(II) 5,10,15,20-tetraisobutylporphyrin (NiTiBuP), Ni(II) 5,15-diphenylporphyrin (NidPP) and Ni(II) 5,15-diisobutylporphyrin (NidiBuP) have been performed by means of high-resolution soft X-ray absorption spectroscopy. It has been found that the low-lying unoccupied electron states in nickel porphyrins are mainly generated by the NiN 4 quasi-molecule: the lowest empty state is the weakly antibonding molecular orbital (MO) of rb 1g symmetry with nearly pure Ni 3d x 2 Ày 2 character, while the next empty state is the e g MO, which has a hybridized Ni 3dp–N 2pp character and reflects p chemical bonding (p-back-donation) between nickel and neighbouring nitrogen atoms of the pyrrole rings. The differences observed in the Ni 2p spectra of nickel porphyrins and phthalocyanines indicate a limited usefulness of the NiN 4 quasi-molecule and a need for its extension to the whole porphyrin (phthalocyanine) macrocycle. As a result, the differences in the Ni 2p spectra of the complexes and in their electronic structure are associated with a torsion of the opposite pyrrole ring planes (NiOEP, NiTiBuP) and the presence of N atoms in meso positions (NiPc). These conclusions are further confirmed by a comparative analysis of the Ni 2p and N 1s absorption spectra for NiPc and NiOEP.

Axial Cu–S(Met) bonds in electron transfer (ET) active sites are generally found to lower their reduction potentials. An axial S(Met) bond is also present in cytochrome c (cyt c) and is generally thought to increase the reduction potential. The highly covalent nature of the porphyrin environment in heme proteins precludes using many spectroscopic approaches to directly study the Fe site to experimentally quantify this bond. Alternatively, L-edge X-ray absorption spectroscopy (XAS) enables one to directly focus on the 3d-orbitals in a highly covalent environment and has previously been successfully applied to porphyrin model complexes. However, this technique cannot be extended to metalloproteins in solution. Here, we use metal K-edge XAS to obtain L-edge like data through 1s2p resonance inelastic X-ray scattering (RIXS). It has been applied here to a bis-imidazole porphyrin model complex and cyt c. The RIXS data on the model complex are directly correlated to L-edge XAS data to develop the complementary nature of these two spectroscopic methods. Comparison between the bis-imidazole model complex and cyt c in ferrous and ferric oxidation states show quantitative differences that reflect differences in axial ligand covalency. The data reveal an increased covalency for the S(Met) relative to N(His) axial ligand and a higher degree of covalency for the ferric states relative to the ferrous states. These results are reproduced by DFT calculations, which are used to evaluate the thermodynamics of the Fe–S(Met) bond and its dependence on redox state. These results provide insight into a number of previous chemical and physical results on cyt c.

Abstract Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d–d and chargetransfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet–triplet and triplet–singlet transitions of the 3d8 configuration.

The electronic structure and the anisotropy of the Al - N π and σ chemical bonding of wurtzite AlN has been investigated by bulk-sensitive total fluorescence yield absorption and soft x-ray emission spectroscopies. The measured N K, Al L1, and Al L2,3 x-ray emission and N 1s x-ray absorption spectra are compared with calculated spectra using first principles density-functional theory including dipole transition matrix elements. The main N 2p - Al 3p hybridization regions are identified at -1.0 to -1.8 eV and -5.0 to -5.5 eV below the top of the valence band. In addition, N 2s - Al 3p and N 2s - Al 3s hybridization regions are found at the bottom of the valence band around -13.5 eV and -15 eV, respectively. A strongly modified spectral shape of Al 3s states in the Al L2,3 emission from AlN in comparison to Al metal is found, which is also reflected in the N 2p - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure and chemical bonding of AlN and Al metal are discussed in relation to the position of the hybridization regions and the valence band edge influencing the magnitude of the large band gap.

We show the first evidence of dissociation during resonant inelastic soft X-ray scattering. Carbon and oxygen K-shell and sulfur L-shell resonant and non-resonant X-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur, L2,3 -> π*, σ* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast the carbon and oxygen spectra show weaker line shape variations and no atomic lines. The spectra are compared to results from ab initio calculations and the discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.