Extended X-ray Absorption Fine Structure Measurements Research Articles

Structure and Dynamics of NaCl/KCl/CaCl2-EuCln (n = 2, 3) Molten Salts.

Modern molten salt reactor design and the techniques of electrorefining spent nuclear fuels require a better understanding of the chemical and physical behavior of lanthanide/actinide ions with different oxidation states dissolved in various solvent salts. The molecular structures and dynamics that are driven by the short-range interactions between solute cations and anions and long-range solute and solvent cations are still unclear. In order to study the structural change of solute cations caused by different solvent salts, we performed first-principles molecular dynamics simulations in molten salts and extended X-ray absorption fine structure (EXAFS) measurements for the cooled molten salt samples to identify the local coordination environment of Eu2+ and Eu3+ ions in CaCl2, NaCl, and KCl. The simulations reveal that with the increasing polarizing the outer sphere cations from K+ to Na+ to Ca2+, the coordination number (CN) of Cl- in the first solvation shell increases from 5.6 (Eu2+) and 5.9 (Eu3+) in KCl to 6.9 (Eu2+) and 7.0 (Eu3+) in CaCl2. This coordination change is validated by the EXAFS measurements, in which the CN of Cl- around Eu increases from 5 in KCl to 7 in CaCl2. Our simulation shows that the fewer Cl- ions coordinated to Eu leads to a more rigid first coordination shell with longer lifetime. Furthermore, the diffusivities of Eu2+/Eu3+ are related to the rigidity of their first coordination shell of Cl-: the more rigid the first coordination shell is, the slower the solute cations diffuse.

Local ordering in Ge/Ge–Sn semiconductor alloy core/shell nanowires revealed by extended x-ray absorption fine structure (EXAFS)

Short-range atomic order in semiconductor alloys is a relatively unexplored topic that may promote design of new materials with unexpected properties. Here, local atomic ordering is investigated in Ge–Sn alloys, a group-IV system that is attractive for its enhanced optoelectronic properties achievable via a direct gap for Sn concentrations exceeding ≈10 at. %. The substantial misfit strain imposed on Ge–Sn thin films during growth on bulk Si or Ge substrates can induce defect formation; however, misfit strain can be accommodated by growing Ge–Sn alloy films on Ge nanowires, which effectively act as elastically compliant substrates. In this work, Ge core/Ge1−xSnx (x ≈ 0.1) shell nanowires were characterized with extended x-ray absorption fine structure (EXAFS) to elucidate their local atomic environment. Simultaneous fitting of high-quality EXAFS data collected at both the Ge K-edge and the Sn K-edge reveals a large (≈ 40%) deficiency of Sn in the first coordination shell around a Sn atom relative to a random alloy, thereby providing the first direct experimental evidence of significant short-range order in this semiconductor alloy system. Comparison of path length data from the EXAFS measurements with density functional theory simulations provides alloy atomic structures consistent with this conclusion.

Evolution of local atomic structure accompanying devitrification of amorphous Ni-Zr alloy thin films

Thin film metallic glasses undergoing devitrification can form partially crystallized or fully crystallized materials with novel structural and magnetic properties. The development of desired and tunable properties of such systems drives the need to understand the mechanism of their thermal evolution at the atomic level. Co-sputtered amorphous Ni-Zr alloy thin films which were thermally annealed in steps of 200°C from room temperature up to 800°C, were observed to undergo an amorphous-to-crystalline transformation. Evolutions in local atomic structure, including oxide formation and depletion during this devitrification process, were determined using a combination of X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The most probable phase of the alloy was determined as Ni7Zr2; undergoing a polymorphous transformation. The slight oxide content in the films was also noted to decrease rapidly as annealing proceeded; leaving the crystallization pathway unhindered. modeling and analyses of XRR and GIXRD data showed that film thickness decreased with annealing while long range order increased. Pair distribution function peak widths were observed to decrease with annealing, indicating a control over structural disorder in the system as it transitioned from the amorphous to crystalline state. Partial atomic distribution in the environment of each constituent was examined at every stage of annealing through EXAFS measurements, which gave proper insight into atomic scale changes to the order present. Detailed analyses through these techniques gave coherent results, thus providing a true picture of the thermal evolution process of devitrification in this technologically useful material.

Investigation of long term stability of W/B4C multilayer structures

The long term stability of as-deposited, annealed, and synchrotron radiation exposed W/B4C multilayer structures was investigated. The multilayer structures were studied using hard X-ray reflectivity, grazing incidence X-ray diffraction (GIXRD), extended X-ray absorption fine structure (EXAFS), and atomic force microscopy (AFM). The structural degradation in annealed and synchrotron radiation exposed samples occurs at faster rate as compared to untreated samples. The structural degradation rate clearly depends on the thickness of B4C layer in multilayer structures. GIXRD measurements confirm the formation of tungsten carbide and boride phases. From EXAFS measurements at the W L3-edge, we find that the increase in the diffusion of oxygen is responsible for the observed structural degradation at faster rate in annealed samples consisting of thinner B4C layer. AFM images reveal that the surface modifications occur at slower rate in untreated samples as compared to annealed samples. Moreover, B4C proves to be an efficient cap layer to protect the as-deposited and annealed multilayer structures from oxidation.

Size and structure of hexanuclear plutonium oxo-hydroxo clusters in aqueous solution from synchrotron analysis.

The size and shape of a water-soluble hexanuclear plutonium cluster were probed by combining synchrotron small-angle X-ray scattering (SAXS) and extended X-ray absorption fine structure (EXAFS). A specific setup coupling both techniques and dedicated to radioactive samples on the MARS beamline endstation at Synchrotron SOLEIL is described. The plutonium hexanuclear cores are well stabilized by the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ligands and this allows a good evaluation of the setup to probe the very small plutonium core. The results show that, in spite of the constrained conditions required to avoid any risk of sample dispersion, the flux and the sample environment are optimized to obtain a very good signal-to-noise ratio, allowing the detection of small plutonium aggregates in an aqueous phase. The structure of the well defined hexanuclear cluster has been confirmed by EXAFS measurements in solution and correlated with SAXS data processing and modelling. An iterative comparison of classical fit models (Guinier or sphere form factor) with the experimental results allowed a better interpretation of the SAXS signal that will be relevant for future work under environmentally relevant conditions.

Chemical disorder in polycrystalline Ni2MnGa thin films

The chemical disorder in magnetic shape memory alloys it is an important parameter that impacts on its magneto-mechanical and electronic properties. In this work, Ni2MnGa thin films were deposited on flexible glass substrates by using DC magnetron sputtering technique. The short-range order/disorder was investigated by means of Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) measurements using at Mn K-edge. Polycrystalline samples of Ni2MnGa with fixed stoichiometry exhibit L21 structure with low residual stress and similar grain sizes. A phenomenological model taking into account three chemical order parameters associated with main chemical anti-site disorders and reliable lattice tetragonal distortions extracted from X-ray diffraction analyses was used to perform systematic computational simulations. The results reveal the persistence of local tetragonal distortions of the crystal structure with L21 structure under when increasing annealing temperatures that are accompanied by a systematic decrease of the anti-site disorder between Ni and Mn atoms and substitutions between Ni and Ga atoms, with the orderly occupation of the atomic sites of Mn and Ga remaining unstable. This work also shows presents a consistent model to perform quantitative analyses of the chemical anti-site disorders through EXAFS measurements in the on Ni2MnGa polycrystalline thin films that preserve both the stoichiometry and the L21 crystalline structure.

Combined EXAFS and MD study to elucidate defect behaviors and stage IV recovery mechanism in heavy ion irradiated molybdenum

The microstructural behaviors of materials control material properties and the recovery mechanism is a key to understanding the microstructural changes induced by irradiation. But the recovery mechanism of many metal materials is not fully understood through traditional research methods. By using Extended X-ray absorption fine-structure (EXAFS) measurements combined with Molecular Dynamics (MD) simulations, we studied the stage IV recovery process through investigating the behaviors of irradiation induced defects (caused by 104 MeV xenon ion beam irradiation) at an elevated temperature (~350 °C) in single crystal Molybdenum (Mo). We distinctly characterized self-interstitial dumbbell defect configurations and simulated their behaviors at this elevated temperature. EXAFS measurements, together with MD simulations and TEM observations, revealed that the mechanism of IV stage recovery is the migration of interstitial type defects (including dumbbells) rather than vacancy type defects. We also discussed the possible states of dumbbells after the stage IV recovery. These results further revealed the nature of the irradiated BCC structure (Mo).

Interface modification of Cr/Ti multilayers with C barrier layer for enhanced reflectivity in the water window regime.

The influence of a carbon barrier layer to improve the reflectivity of Cr/Ti multilayers, intended to be used in the water window wavelength regime, is investigated. Specular grazing-incidence X-ray reflectivity results of Cr/Ti multilayers with 10 bilayers show that interface widths are reduced to ∼0.24 nm upon introduction of a ∼0.3 nm C barrier layer at each Cr-on-Ti interface. As the number of bilayers increases to 75, a multilayer with C barrier layers maintains almost the same interface widths with no cumulative increase in interface imperfections. Using such interface-engineered Cr/C/Ti multilayers, a remarkably high soft X-ray reflectivity of ∼31.6% is achieved at a wavelength of2.77 nm and at a grazing angle of incidence of 16.2°, which is the highest reflectivity reported so far in the literature in this wavelength regime. Further investigation of the multilayers by diffused grazing-incidence X-ray reflectivity and grazing-incidence extended X-ray absorption fine-structure measurements using synchrotron radiation suggests that the improvement in interface microstructure can be attributed to significant suppression of inter-diffusion at Cr/Ti interfaces by the introduction of C barrier layers and also due to the smoothing effect of the C layer promoting two-dimensional growth of the multilayer.

Electron beam irradiation induced changes in local structure of simulated waste bearing sodium borosilicate glasses

Time differential perturbed angular correlation (TDPAC) and Extended X-ray absorption fine structure (EXAFS) studies have been carried out on electron beam (EB) irradiated sodium borosilicate (NBS) and simulated waste oxide loaded sodium borosilicate (SNBS) glasses with a view to investigate the effect of self β-irradiation in vitrified high level waste. NBS and SNBS glasses were synthesized and doped with 1.5% HfO2. For TDPAC studies the glasses were doped with 181Hf probe, while for EXAFS studies measurements were carried out at and around Hf LIII edge. TDPAC and EXAFS acquisition were performed before and after electron beam irradiation doses up to 10 MGy for both NBS and SNBS glasses. Fourier transforms of the TDPAC spectra show broad frequency distribution reminiscent of the disordered glass matrix, with increase in hyperfine interaction frequency in irradiated glasses with respect to unirradiated ones as well as with increasing EB dose. On the other hand, the width of the frequency distribution was found to decrease with EB dose. No change in asymmetry of the electric field gradient was observed in irradiated glasses with respect to unirradiated ones. These observations indicate that while there is no indication of appearance of micro-crystallinity in the glasses up to EB dose of 10 MGy, local structural changes around Hf do take place with EB irradiation in both the glasses. No change in metric parameters (Hf-O bond distance and coordination number of Hf) was observed from EXAFS measurements on both NBS and SNBS glasses up to EB dose of 10 MGy.

Extended x-ray absorption fine structure spectroscopy of stretched magnetic films on flexible substrate

This study investigates element-specific atomic distances and strains in ferromagnetic (FM) nano-thin films deposited on a flexible substrate, which can be modulated by stretching the substrate. Extended x-ray absorption fine structure (EXAFS) spectroscopy was used for the experiments. Both in-plane tensile and out-of-plane compressive strains were investigated by applying %-order tensile strains to the substrate. The atomic distance changes induced by stretching the substrate were quantitatively discussed by considering the Poisson compression, crystalline orientations of the FM metals, and polarization in the EXAFS measurement. Consequently, the ratio of strain transfer from the flexible substrate to the FM layers was estimated to be about 30% and 60% in Co and Fe nano-thin films, respectively. The strain transfer in Co films with different Co or Pt underlayer thicknesses was also measured. The results are compared with the thickness dependence of the effective magnetoelastic coupling constant, which represents the magnitude of the inverse magnetostriction effect. Although the strain transfer partially contributes to the thickness dependence, the difference in the Co lattice constant is suggested to have a significant influence on the effective magnetoelastic coupling constant.

Enhanced CO2 Electroreduction on Neighboring Zn/Co Monomers by Electronic Effect

AbstractIt is of great significance to reveal the detailed mechanism of neighboring effects between monomers, as they could not only affect the intermediate bonding but also change the reaction pathway. This paper describes the electronic effect between neighboring Zn/Co monomers effectively promoting CO2 electroreduction to CO. Zn and Co atoms coordinated on N doped carbon (ZnCoNC) show a CO faradaic efficiency of 93.2 % at −0.5 V versus RHE during a 30‐hours test. Extended X‐ray absorption fine structure measurements (EXAFS) indicated no direct metal–metal bonding and X‐ray absorption near‐edge structure (XANES) showed the electronic effect between Zn/Co monomers. In situ attenuated total reflection‐infrared spectroscopy (ATR‐IR) and density functional theory (DFT) calculations further revealed that the electronic effect between Zn/Co enhanced the *COOH intermediate bonding on Zn sites and thus promoted CO production. This work could act as a promising way to reveal the mechanism of neighboring monomers and to influence catalysis.

Enhanced CO2 Electroreduction on Neighboring Zn/Co Monomers by Electronic Effect.

It is of great significance to reveal the detailed mechanism of neighboring effects between monomers, as they could not only affect the intermediate bonding but also change the reaction pathway. This paper describes the electronic effect between neighboring Zn/Co monomers effectively promoting CO2 electroreduction to CO. Zn and Co atoms coordinated on N doped carbon (ZnCoNC) show a CO faradaic efficiency of 93.2 % at -0.5 V versus RHE during a 30-hours test. Extended X-ray absorption fine structure measurements (EXAFS) indicated no direct metal-metal bonding and X-ray absorption near-edge structure (XANES) showed the electronic effect between Zn/Co monomers. In situ attenuated total reflection-infrared spectroscopy (ATR-IR) and density functional theory (DFT) calculations further revealed that the electronic effect between Zn/Co enhanced the *COOH intermediate bonding on Zn sites and thus promoted CO production. This work could act as a promising way to reveal the mechanism of neighboring monomers and to influence catalysis.

Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)2 Complex.

The molecular structure of the 8-hydroxyquinoline–bis (2-phenylpyridyl) iridium (IrQ(ppy)2) dual emitter organometallic compound is determined based on detailed 1D and 2D nuclear magnetic resonance (NMR), to identify metal-ligands coordination, isomerization and chemical yield of the desired compound. Meanwhile, the extended X-ray absorption fine structure (EXAFS) was used to determine the interatomic distances around the iridium ion. From the NMR results, this compound IrQ(ppy)2 exhibits a trans isomerization with a distribution of coordinated N-atoms in a similar way to facial Ir(ppy)3. The EXAFS measurements confirm the structural model of the IrQ(ppy)2 compound where the oxygen atoms from the quinoline ligands induce the splitting of the next-nearest neighboring C in the second shell of the Ir3+ ions. The high-performance liquid chromatography (HPLC), as a part of the detailed molecular analysis, confirms the purity of the desired IrQ(ppy)2 organometallic compound as being more than 95%, together with the progress of the chemical reactions towards the final compound. The theoretical model of the IrQ(ppy)2, concerning the expected bond lengths, is compared with the structural model from the EXAFS and XRD measurements.

Structural and magnetic properties of FePt-Tb alloy thin films

We have studied structural and magnetic properties of ${(\mathrm{FePt})}_{1\ensuremath{-}x}\mathrm{T}{\mathrm{b}}_{x}$ thin films grown at elevated temperatures on MgO(100) substrates. The incorporation of Tb into the chemically ordered $\mathrm{L}{1}_{0}$ FePt lattice gives rise to considerable changes in the structural and magnetic properties, depending on the Tb content and the deposition temperature. When grown at $770{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, pronounced $L{1}_{0}$ ordering of the initial FePt phase is present. It vanishes gradually with Tb addition, thereby forming additional crystalline Tb-Pt phases at higher Tb content. These structural changes are accompanied by a strong reduction of the perpendicular magnetic anisotropy with increasing Tb content, finally resulting in a soft magnetic material with in-plane easy-axis magnetization. Extended x-ray absorption fine-structure measurements were performed to examine the possible incorporation of Tb into the FePt lattice. Based on the number of Pt first neighbors, the transformation from the initial tetragonal $L{1}_{0}$ structure to the chemically disordered fcc ($A$1) phase with increasing Tb content could be firmly concluded. In a further sample series, FePt was grown at a lower temperature of 530 \ifmmode^\circ\else\textdegree\fi{}C, which leads to reduced initial $L{1}_{0}$ chemical ordering. Adding Tb results in strong elastic stress in the lattice, eventually causing full amorphization of the film. Interestingly, in this case, a spin-reorientation transition from in-plane to out-of-plane magnetic easy axis is found at low temperatures, which is associated with an anisotropic chemical short-range order present in the amorphous phase. Furthermore, x-ray magnetic circular dichroism studies at the $\mathrm{Fe}\phantom{\rule{0.28em}{0ex}}{L}_{3,2}$ and Tb ${M}_{5,4}$ edges for all samples reveal strong antiferromagnetic coupling between Fe and Tb, resulting in a reduction of the net magnetization of the film.

Depth-resolved local atomic structure of Fe/Cr multilayer film with GMR effect: Experimental results

A subnanometric resolution method for studying the local atomic structure of interface and surface of low contrast multilayered nanoheterostructure thin films is applied to the Fe/Cr multilayer sample with GMR (Giant Magnetoresistance) effect. We consider combination of the X-ray reflectivity (XRR) and the Extended X-ray absorption Fine Structure (EXAFS) spectroscopy with angular resolution. The XRR experiment has been carried out according to standard procedure using a specialized X-ray diffractometer «Empyrean» at the Institute of Metal Physics (Ekaterinburg). We have applied a measurement method proposed earlier by V. P. Romanov et al. This approach allowed us to separate the diffuse and pure specular contributions. To determine the concentration depth-profile of element from XRR data, we have implemented the Levenberg-Marquardt (L-M) algorithm for nonlinear inverse problem. Thus, the phase problem for X-ray specular reflectivity has been solving. The EXAFS measurements has been performed using synchrotron facilities (National Research Centre “Kurchatov Institute”). {The Fe and Cr K absorption spectra} were recorded in fluorescence mode with angular resolution. The experimental results for depth-resolved local atomic structure of Fe/Cr multilayer with GMR effect has been obtained. A depth resolution of 2-3 Å was reached. Atomic structure of Fe and Cr atoms located at seven depth points including interface for the Al2O3/Cr(100 Å)/[Fe(8 Å)/Cr(10,5 Å)]2/Cr(20 Å) multilayered sample was obtained. It was shown what chromium oxides were present on the surface of the sample..

Effect of growth temperature on the structural and magnetic properties of the pulsed laser deposited Co2FeAl thin films

A set of Co2FeAl (CFA) Heusler alloy thin films have been prepared at different substrate temperatures using the Pulsed Laser Deposition (PLD) technique and the effect of growth temperature on the structural and magnetic properties of the films have been studied in detail. Preliminary structural characterization of the films have been carried out by Grazing Incidence X-ray diffraction (GIXRD) measurements, while the thickness and roughness of the films have been estimated by Grazing incidence X-ray reflectivity (GIXR) measurements. The element specific X-ray absorption spectroscopy (XAS) technique comprising of both Extended X-ray absorption fine structure (EXAFS) and X-ray near edge structure (XANES) measurements have been carried out on the samples both at Fe and Co K edges and the results have been analysed to quantitatively determine the various bond lengths around both Fe and Co sites which ultimately gives information regarding relative strength of d-d hybridization over p-d hybridization in the samples. Finally the magnetic behavior of the samples have been measured thoroughly as a function of temperature and magnetic field and variation of the magnetization of the samples on the crystallite size and substrate temperature has been studied. The nature of the spin wave in the thermal demagnetization of spontaneous magnetization has also been explored. The structural information obtained from EXAFS measurements have been correlated with the magnetic properties of the samples.

Particle size effect on structural and optical properties of Y2O3:Nd3+ nanoparticles prepared by coconut water-assisted sol-gel route

Pure and Nd3+ doped Y2O3 samples were produced under different calcination conditions via a modified sol-gel route. The powders were characterized by Extended X-Ray Absorption Fine Structure (EXAFS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) measurements. EXAFS measurement at Y K edge of amorphous powders showed a more organized structure for samples produced at higher pH of starting sol, which in turn facilitated the crystallization of the cubic Y2O3 phase at lower temperatures. On the other hand, the quantitative EXAFS analysis of the crystalline samples showed that the produced nanomaterials presented a high degree of crystallinity, even for samples with the crystallite sizes of about 6 nm. The behavior of fluorescence emission intensity of Nd doped samples was studied considering the influence of adsorbed molecules onto particle’ surfaces and energy transfer processes between the dopant ions.

Improved geochemical modeling of lead solubility in contaminated soils by considering colloidal fractions and solid phase EXAFS speciation

Lead (Pb) is a common contaminant in soils at e.g. mining, shooting range, and glassworks sites. In order to make reliable risk assessments and appropriate decisions on various “gentle remediation options”, such as applying phosphate, compost, or zero-valent iron to soils, the binding mechanism of Pb and its speciation needs to be known. Multi-surface geochemical equilibrium models are useful tools for estimating trace metal solubility and speciation, but for Pb the predictions are often poor. This study evaluates the recent parameterization for Pb in the Visual MINTEQ code for its ability to predict the solubility of Pb at different pH values in four historically contaminated Swedish soils. As an independent validation of the model performance, the modeled solid-phase speciation was compared to measured Pb speciation retrieved using extended X-ray absorption fine structure (EXAFS) spectroscopy. Furthermore, potential artefacts by the presence of Pb colloids were investigated by filtering solutions through both 0.45 μm and 10 kDa filters. The model accuracy for predicting Pb solubility was improved compared with previous studies producing log root mean square error (RMSE) values below 0.42 in three out of four soils, just by using generic assumptions. The use of ultrafiltered (<10 kDa) instead of the 0.45 μm-filtered Pb concentrations lowered the RMSE with ∼0.4 log units in two soils, giving a more accurate evaluation of the model performance. EXAFS proved to be a useful tool for validating and constraining the model, since the solid phase speciation did not exactly agree with the modeled results using default assumptions. However, a sample-specific optimization of the amount of “active” solid organic matter and Al + Fe hydroxides resulted in improved prediction of Pb solubility as well as better agreement with the EXAFS measurements. Solubility of Pb in the fourth, As-rich soil was probably controlled by Pb5(AsO4)3Cl (mimetite) with a solubility product constant of 10−83.53.

Deciphering the Role of Charge Compensator in Optical Properties of SrWO4:Eu3+:A (A = Li+, Na+, K+): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption.

Studies have been carried out to understand the specific role of the alkali charge compensator on the luminescence properties of an alkali ion (Li+, Na+, and K+) codoped SrWO4:Eu phosphor. The oxidation state of the europium ion was found to be +3 on the basis of X-ray absorption near edge structure (XANES) measurements. This is the first report of its kind where opposite effects of Li+ ion and Na+/K+ ions on photoluminescence intensity have been observed. Li+ ion codoping enhanced the photoluminescence intensity from SrWO4:Eu3+ phosphor while Na+/K+ ion codoping did not. On the other hand, the luminescence lifetime is maximum for the Na+ ion codoped sample and minimum for the Li+ ion codoped sample. The results could be explained successfully using time-resolved luminescence, positron annihilation lifetime spectroscopy (PALS), and extended X-ray absorption fine structure (EXAFS) spectroscopy measurements. Changes in the Eu-O bond length and Debye-Waller Factor (σ2) upon Li+/Na+/K+ codoping were monitored through EXAFS measurements. PALS also highlighted the fact that Li+ codoping is not contributing to reduction in the cation vacancies and might be occupying interstitial sites rather than lattice positions due to its very small size. On europium doping there is lowering in symmetry of SrO8 polyhedra from S4 to C6, which is reflected in an intense electric dipole transition in comparison to the magnetic dipole transition. This is also corroborated using trends in Judd-Ofelt parameters. The results have shown that the luminescence lifetime is better when the vacancy concentration is lower as induced by Na+ and K+ codoping, while the emission intensity is higher in the samples when distortion around Eu3+ is reduced as induced by Li+ codoping.

Structural properties of nano-porous GaSb prepared by swift heavy-ion irradiation

Abstract We are investigating the structural and optical properties of nano-porous GaSb formed by swift heavy ion irradiation using a combination of high resolution structural characterization techniques including synchrotron based small- and wide-angle X-ray scattering (SAXS/WAXS) and extended X-ray absorption fine structure (EXAFS), as well as optical measurements like Raman and Fourier transform infrared spectroscopy. In contrast to nano-porous GaSb prepared by low energy ion irradiation, the swift heavy ion irradiated samples do not show any sign of homo-polar bonding typical for amorphous materials in EXAFS measurements despite the observed significant structural disorder. Furthermore, X-ray diffraction and Raman-spectroscopy reveal the presence of small (