Edge X-ray Absorption Spectroscopy Research Articles

Speciation of toxic metals in metal finishing filter cake by X-ray absorption spectroscopy

The speciation of Cr, Zn, Cu and Pb in two metal finishing filter cakes (TX and ST) was investigated by X-ray absorption spectroscopy (XAS) complemented by X-ray fluorescence (XRF) and X-ray diffraction (XRD). XRF showed that concentrations of Cr, Zn, Cu and Pb were 1.4%, 0.19%, 0.20% and 0.01%, respectively, in TX, and 12.6%, 3.3%, 1.3% and 0.21% in ST. No crystalline phases were detected in TX by XRD whereas ST was dominated by calcite. Cr and Fe K edge XAS showed Cr to be trivalent and octahedrally coordinated, co-precipitated with Fe as CrxFe1-x-(oxy)hydroxides in both filter cakes. Zn, P and Ca K edge XAS showed that 2ZnCO3∙3Zn(OH)2 and Zn3(PO4)2 were the dominant zinc-containing phases, with combined tetrahedral and octahedral coordination; Zn phases were slightly more crystalline in TX than ST. Pb L3 edge X-ray absorption near edge spectroscopy (XANES) found that Pb was likely adsorbed on amorphous SiO2. Cu, Si and S K edge XAS showed that all Cu was divalent, and the dominant copper phases were found to be Cu2Cl(OH)3, Cu(OH)2 and CuSO4·5H2O for ST, whereas Cu appeared to adsorb to amorphous SiO2 for TX, which contained much less Pb. Cr is thus immobilized in the filter cakes in a phase with low solubility at environmentally feasible pH values, whereas Zn, Cu and Pb could be released when the pH decreases below 8 or above 11. These findings are significant for the development of waste management regulations and/or metal recovery methods (e.g., hydro/pyrometallurgy).

Cu(I) Coordination Compounds Conjugated to Au Nanorods for Future Applications in Drug Delivery: Insights in Molecular, Electronic and Cu Local Structure in Solid and Liquid Phase.

In the framework of the design, synthesis and testing of a library of copper complexes and nanostructured assemblies potentially endowed with antitumor and antiviral activity and useful for several applications, from drugs and related delivery systems to the development of biocidal nanomaterials, we present the detailed spectroscopic investigation of the molecular and electronic structure of copper-based coordination compounds and of a new conjugated system obtained by grafting Cu(I) complexes to gold nanorods. More in detail, the electronic and molecular structures of two Cu complexes and one AuNRs/Cu-complex adduct were investigated by X-ray photoelectron spectroscopy (XPS), synchrotron-induced XPS (SR-XPS) and near edge X-ray absorption spectroscopy (NEXAFS) in solid state, and the local structure around copper ion was assessed by X-ray absorption spectroscopy (XAS) both in solid state and water solution for the AuNRs/Cu-complex nanoparticles. The proposed multi-technique approach allowed to properly define the coordination geometry around the copper ion, as well as to ascertain the molecular structures of the coordination compounds, their stability and modifications upon interaction with gold nanoparticles, by comparing solid state and liquid phase data.

Coupled Experimental-Theoretical Characterization of a Carbon Electrode in Vanadium Redox Flow Batteries using X-ray Absorption Spectroscopy.

Vanadium redox flow batteries (VRFBs) have emerged as promising solutions for stationary grid energy storage due to their high efficiency, scalability, safety, near room-temperature operation conditions, and the ability to independently size power and energy capacities. The performance of VRFBs heavily relies on the redox couple reactions of V2+/V3+ and VO2+/VO2+ on carbon electrodes. Therefore, a thorough understanding of the surface functionality of carbon electrodes and their propensity for degradation during electrochemical cycles is crucial for designing VRFBs with extended lifespans. In this study, we present a coupled experimental-theoretical approach based on carbon K edge X-ray absorption spectroscopy (XAS) to characterize carbon electrodes prepared under different conditions and identify relevant functional groups that contribute to unique spectroscopic features. Atomic models were created to represent functional groups, such as hydroxyl, carboxyl, methyl, and aldehyde, bonded to carbon atoms in either sp2 or sp3 environments. The interactions between functionalized carbon and various solvated vanadium complexes were modeled using density functional theory. A library of carbon K-edge XAS spectra was generated for distinct carbon atoms in different functional groups, both before and after interacting with solvated vanadium complexes. We demonstrate how these simulated spectra can be used to deconvolve ex situ experimental spectra measured from carbon electrodes and to track changes in the electrode composition following immersion in different electrolytes or extended cycling within a functional VRFB. By doing so, we identify the active species present on the carbon electrodes, which play a crucial role in determining their electrochemical performance.

Texture, electronic and magnetic states of Mn atoms in polycrystalline MnSi thin films facing a c-sapphire substrate studied by soft X-ray magnetic circular dichroism

Polycrystalline MnSi is a highly efficient magnetic skyrmionic material and information carriers for future spintronic devices, deposited on a c-cut sapphire substrate by magnetron sputtering with a low base pressure. Due to their fascinating crystal structures and spin textures these Mn-based silicides are most extensively studied now a days. In order to study the appearance of any impure phases like MnxSiy, hysteresis behavior and the inception of ferromagnetic/superparamagnetic domains present in the MnSi film, we have performed X-ray diffraction (XRD), XRD pole figures in stereographic projection, vibrating sample magnetometry and powerful element specific X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism techniques. The room temperature hysteresis curve points towards the phenomenon of long-range ferromagnetic ordering. The Mn L2,3 edge XAS spectra did not show a Mn2+-like multiplet structure. The overall magnetization increases with the increase in applied magnetic field from 0.1 T to 2 T on MnSi thin film. The observed spin and orbital magnetic moments ∼ 0.03 ̶ 0.1 μB and 0.01 to 0.04 μB, respectively.

Dielectric, magnetic and structural properties of Co doped CeO2 powders

Bulk samples of Ce1-xCoxO2 (x = 0.00 to 0.05) are prepared using solid state reaction technique. X-ray diffraction (XRD) results show a continuous decrease in the unit cell volume of Co doped CeO2 samples which indicates the substitutional doping of Co into the CeO2 lattice up to the doping concentration of x = 0.05. Field emission scanning electron microscopy (FESEM) images depict the formation of close packed particles of unusual morphology of size of 1–3 μm. X-ray absorption spectroscopy (XAS) at Ce M5,4 edge and Co L3,2 edge confirm the presence of Ce4+ and Co2+ ions, respectively. O K edge XAS conveys modification in electronic structure properties via formation of oxygen ion vacancies upon Co doping concentrations. Our results show that the observed large dielectric constants (ε′and ε'') and room temperature ferromagnetism are the intrinsic properties of the Co doped CeO2, which may offer this material in dielectric and magnetic devices applications.

Insights into structure and reactivity of MOFs by ambient pressure soft X-ray absorption spectroscopy

Metal–Organic Frameworks (MOFs) are nanostructured porous materials made up by metal cations and organic linkers forming three-dimensional structures. Since their discovery, the local properties of metal centers in MOFs have often been studied with hard X-ray absorption spectroscopy that is not a surface sensitive technique. Here, we employ the ambient-pressure soft X-ray absorption spectroscopy, using a newly developed experimental setup, to unveil the formation mechanism of surface defective sites in the prototypical Cu(II)-based MOF HKUST-1, as well as the reactivity and selectivity of these sites towards CO2 from the analysis of the Cu L3-edge near edge X-ray absorption spectroscopy (NEXAFS) data. We observe that, upon thermal heating, Cu(I) defects are formed more abundantly on the surface of the material as compared to the bulk, a process that is almost fully reversed when the MOF is exposed to CO2, even when mixed with H2. Additionally, we propose a structure and a formation mechanism for such defective sites, supported by theoretical DFT-based calculations.

Site occupancies in a chemically complex σ-phase from the high-entropy Cr–Mn–Fe–Co–Ni system

Site occupancies in a single-phase σ-intermetallic compound of composition Cr46Mn15.2Fe16.3Co17Ni5.5 (in at.%) were studied. To the best of the authors’ knowledge, such a complex analysis with 5 elements occupying 5 different sites has never been tackled before and is addressed here using cutting edge X-ray diffraction techniques, absorption spectroscopy and simulations. Resonant powder diffraction data were collected at the K-edges of each of the five elements and the site occupancies were refined by a joint Rietveld analysis. Dispersion coefficients were retrieved independently from tabulated values, Kramers-Kronig relations and reference samples. Additional Extended X-ray Absorption Fine Structure (EXAFS) measurements were used to confirm the site occupancies and bond lengths. The site occupancies were independently obtained by a thermodynamic approach based on the enthalpies of formation of the 55 = 3125 configurations generated by the ordered distribution of the five components on the five sublattices, derived from a machine learning approach based on a DFT database. Overall, the calculations and experiments are in excellent agreement and reveal that the σ phase can accommodate a considerable degree of disorder, which consequences for thermodynamic modeling are discussed. The configurational entropy (S) of the σ phase represents 84% of that of a fully disordered alloy with the same composition, which is much larger than that expected for a fully ordered intermetallic phase (S = 0). The corresponding entropic stabilization is one of the reasons for the fact that the σ phase is one of the most important intermetallic that precipitates in high-entropy alloys and many engineering materials.

Effects of Ni/Co doping on structural and electronic properties of 122 and 112 families of Eu based iron pnictides

Superconductivity in high-temperature superconductors such as cuprates or iron pnictides is typically achieved by hole or electron doping and it is of great interest to understand how doping affects their properties leading to superconductivity. To study it we conducted Fe and As K edge x-ray absorption spectroscopy measurements on several electron doped compounds from the 112 and 122 family of Eu-based iron pnictides. XANES and EXAFS results confirm that dopants are located at expected sites. For both families we found an electron charge redistribution between As and Fe occurring with doping. The changes it caused are stronger in the 112 family and they are bigger at As sites, which indicates that doped charges are predominantly localized on the dopant site. However, the results obtained do not provide clues why Ni doping in 122 family does not lead to occurrence of superconductivity.

3d and 5d electronic structures and orbital hybridization in Ba- and Ca-doped La2CoIrO6 double perovskites

Here we present a detailed investigation of the Co and Ir local electronic structures in ${\mathrm{La}}_{1.5}{A}_{0.5}{\mathrm{CoIrO}}_{6}$ ($A=\mathrm{Ba}$, Ca) compounds in order to unravel the orbital hybridization mechanism in these CoIr-based double perovskites. Our results of x-ray powder diffraction, ac and dc magnetization, Co and Ir ${L}_{2,3}$-edge and Co $K$-edge x-ray absorption spectroscopy and x-ray magnetic circular dichroism suggest a competition between magnetic interactions. A dominant antiferromagnetic coupling is found to be responsible for the ferrimagnetic behavior observed for $A=\mathrm{Ca}$ below $\ensuremath{\sim}96\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the competing magnetic phases, and the cationic disorder in this compound giving rise to a spin-glass state at low temperatures. For the $A=\mathrm{Ba}$, on the other hand, there is no evidence of long-range order down to its spin-glass transition temperature. The remarkably different magnetic properties observed between these two compounds are discussed in terms of the structural distortion that alters the strength of the Co-Ir couplings, with a relevant role played by the Co $3d\phantom{\rule{4pt}{0ex}}{e}_{g}--\mathrm{Ir} 5d\phantom{\rule{4pt}{0ex}}{j}_{\mathrm{eff}}=1/2$ hybridization.

Effect of substrate on interfacial electronic properties of ferrocene thin films

Ferrocene molecular thin films on conducting substrates have potential for novel molecular electronic devices. Based on X-ray absorption spectroscopy and photoemission spectroscopic techniques, we have analyzed electronic properties of ferrocene thin films nano-junctions on layered highly oriented pyrolytic graphite (HOPG) and epitaxially grown graphene on Ni(1 1 1) substrates. Fe L edge analysis indicates that layered structure of HOPG has significant impact on room temperature desorption of ferrocene as compared to grapheme on Ni(1 1 1) substrate. C-K edge XAS spectrum reveal that ferrocene molecules do not have preferred orientation for adsorption on grapheme grown on Ni(1 1 1) substrate. In addition, X-ray absorption spectroscopy (XAS) reveals that there is no change in iron atom oxidation state suggesting that ferroence interaction is feeble with grapheme on Ni(1 1 1) substrate and HOPG.

Spectroscopic Manifestations and Implications for Catalysis of Quasi-d10 Configurations in Formal Gold(III) Complexes.

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand σ-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal CuIII complex [Cu(CF3 )4 ]1- , in which the metal center tries to populate its formally unoccupied 3dx2-y2 orbital via σ-bonding, leading to a reduced d10 CuI description. However, Au L3 -edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the AuIII species is still possible, showing that a genuine d10 configuration is not achieved. We also find an increased electron-sharing nature of the σ-bonds in the AuI species, relative to their AgI and CuI analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5dx2-y2 or 6s orbital, respectively, in bonding, indicating why AuI and AuIII complexes often have similar reactivity.

Spectromicroscopy of Nanoscale Materials in the Tender X-Ray Regime Enabled by a High Efficient Multilayer-Based Grating Monochromator.

The combination of near edge X-ray absorption spectroscopy with nanoscale X-ray imaging is a powerful analytical tool for many applications in energy technologies, catalysis, which are critical to combat climate change, as well as microelectronics and life science. Materials from these scientific areas often contain key elements, such as Si, P, S, Y, Zr, Nb, and Mo as well as lanthanides, whose X-ray absorption edges lie in the so-called tender photon energy range 1.5-5.0keV. Neither conventional grazing incidence grating nor crystal monochromators have high transmission in this energy range, thereby yielding the tender photon energy gap. To close this gap, a monochromator setup based on a multilayer coated blazed plane grating and plane mirror is devised. The measurements show that this novel concept improves the photon flux in the tender X-ray regime by two-orders-of-magnitude enabling previously unattainable laboratory and synchrotron-based studies. This setup is applied to perform nanoscale spectromicroscopy studies. The high photon flux provides sufficient sensitivity to obtain the electronic structure of Mo in platinum-free MoNi4 nanoparticles for electrochemical energy conversion. Additionally, it is shown that the chemical bonding of nano-structures in integrated circuits can be distinguished by the electronic configuration at the Si-K edge.

Strain-modulated anisotropic electronic structure in superconducting RuO2 films

The binary ruthenate, ${\mathrm{RuO}}_{2}$, has been the subject of intense interest due to its itinerant antiferromagnetism and strain-induced superconductivity. The strain mechanism and its effect on the microscopic electronic states leading to the normal and superconducting state, however, remain undisclosed. Here, we investigate highly strained epitaxial (110) ${\mathrm{RuO}}_{2}$ films using polarization-dependent oxygen $K$-edge x-ray absorption spectroscopy (XAS). Through the detection of pre-edge peaks arising from O:$2p$ - Ru:$4d$ hybridization, we uncover the effects of epitaxial strain on the orbital/electronic structure near the Fermi level. Our data show robust strain-induced shifts of orbital levels and a reduction of hybridization strength. Furthermore, we reveal a pronounced in-plane anisotropy of the electronic structure along the $[110]/[1\overline{1}0]$ directions naturally stemming from the symmetry-breaking epitaxial strain of the substrate. The ${B}_{2g}$ symmetry component of the epitaxially enforced strain breaks a sublattice degeneracy, resulting in an increase of the density of states at the Fermi level (${E}_{F}$), possibly paving the way to superconductivity. These results underscore the importance of the effective reduction from tetragonal to orthorhombic lattice symmetry in (110) ${\mathrm{RuO}}_{2}$ films and its relevance towards the superconducting and magnetic properties.

Topochemical Synthesis of LiCoF3 with a High-Temperature LiNbO3-Type Structure.

A novel perovskite fluoride, LixCoF3, which has an exceptionally low tolerance factor (0.81), has been synthesized via low-temperature lithium intercalation into a distorted ReO3-type fluoride CoF3 using organolithium reagents. Interestingly, this reaction is completed within 15 min at room temperature. Synchrotron X-ray diffractometry and optical second harmonic generation at room temperature have revealed that this compound shows a high-temperature LiNbO3-type structure (space group: R3̅c) involving Li-Co antisite defects and A-site splitting along the c direction. A-site splitting is consistent with the prediction based on hybrid Hartree-Fock density functional theory calculations. Co-L2,3 edge X-ray absorption spectroscopy, as well as bond valence sum analysis, has verified the divalent oxidation state of Co ions in the lithiated phase, suggesting that its composition is close to LiCoF3 (x ≈ 1). This compound exhibits a paramagnetic-to-antiferromagnetic transition at 36 K on cooling, accompanied by weak ferromagnetic ordering. The synthetic route based on low-temperature lithiation of metal fluorides host paves the way for obtaining a new LiNbO3-type fluoride family.

(Digital Presentation) Investigations into the Capacity Degradation Due to an Electronic Structural Change in Homogenous Boron-Substituted Ni-Rich Layered Oxides

Ni-rich layered oxides (LiNixCoyMnzO2, x≥0.8, x+y+z=1) would fulfil the energy density requirements of the automobile industry since they offer outstanding capacities at relatively high mean voltages and sufficient power densities1-3. However, the materials still show significant capacity and voltage fade which requires substantial research. Recently we have shown that the electronic structure is the key to understand the performance but also the failure of the materials1. Thus, we intend to modify the electronic structure using anionic dopants such as Boron. Thus, homogenous B-substituted NCM811s (BNCM811_x%, x% means the x at. % of Boron) are synthesized and the materials reveal a significant change in the electronic structure as evident from x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption spectroscopy (NEXAFS). Interestingly, a shift of the so called H2-H3 peak4 to higher potentials was observed by Boron substitution and BNCM811s_2% shows relative higher initial discharge capacity (Figure 1A.) at a slightly higher mean voltage, but a lower cycling stability compared to NCM811 (Figure 1B.).The H2-H3 differential capacity peak (Figure 1C) might also include oxygen release5, which is one of the main reasons restricting the cycling stability. Near edge x-ray absorption spectroscopy (NEXAFS) shows that the H2-H3 peak corresponds to a reaction from Ni3+ to Ni2+ (upon charge) and Ni2+ to Ni3+ (upon discharge) which suggest a reaction like NiO2 ⥂ NiO + ½ O2 as the underlying process. At the same time, an Oxygen K peak at 531 eV appears in the NEXAFS spectra, which was assigned to O-O formation in the host structure of Li-rich materials6, 7. Note that the electronic structure of the materials was determined in 5 mAh/g steps over the H2-H3 peak and due to the high resolution, this process became visible for the first time. The findings suggest that dimer formation is not only a phenomenon of Li-rich materials but can also be found in Ni-rich layered oxides at high states of charge.The origin of dimer formation and oxygen release can be traced back to the electronic configuration of Ni. Charge transfer multiplet calculations reveal, that Ni2+ reacts to covalent Ni3+ upon charge (and vice versa upon discharge)1. Ni3+ has a 3d7 electronic state, whose low spin configuration is more preferred than its high spin configuration. Thus, Ni3+ is more prone to Jahn-Teller (JT) distortions and tends to form covalent bonds. Consequently, the electrons are more bound to the individual sites making a further oxidation of the transition metal almost impossible. In conclusion, Boron substitution helps us to understand the function and failure of layered oxides in Li-ion batteries on an atomistic scale and the findings can be used as a design guide for future materials. K. Kleiner, C. A. Murray, C. Grosu, B. Ying, M. Winter, P. Nagel, S. Schuppler and M. Merz, Journal of The Electrochemical Society, 2021.J. Zhao, W. Zhang, A. Huq, S. T. Misture, B. Zhang, S. Guo, L. Wu, Y. Zhu, Z. Chen and K. Amine, Advanced Energy Materials, 2017, 7, 1601266.S.-J. Yoon, K.-J. Park, B.-B. Lim, C. S. Yoon and Y.-K. Sun, Journal of the Electrochemical Society, 2014, 162, A3059.S. Jamil, G. Wang, L. Yang, X. Xie, S. Cao, H. Liu, B. Chang and X. Wang, Journal of Materials Chemistry A, 2020, 8, 21306-21316.K. Märker, P. J. Reeves, C. Xu, K. J. Griffith and C. P. Grey, Chemistry of Materials, 2019, 31, 2545-2554.E. Hu, X. Yu, R. Lin, X. Bi, J. Lu, S. Bak, K.-W. Nam, H. L. Xin, C. Jaye and D. A. Fischer, Nature Energy, 2018, 3, 690-698.K. Kleiner, B. Strehle, A. R. Baker, S. J. Day, C. C. Tang, I. Buchberger, F.-F. Chesneau, H. A. Gasteiger and M. Piana, Chemistry of Materials, 2018, 30, 3656-3667. Figure 1

Oxidation of two-dimensional electrides: Structural transition and the formation of half-metallic channels protected by oxide layers

Based on first-principles calculations, we performed a systematic study of the energetic stability, structural characterization, and electronic properties of the fully oxidized ${A}_{2}B$ electrenes, with the following combinations: (i) $A$ = Ca, Sr, and Ba for $B$ = N; (ii) $A$ = Sr and Ba for $B$ = P; and ${\mathrm{Y}}_{2}\mathrm{C}$ and ${\mathrm{Ba}}_{2}\mathrm{As}$. We have considered one side oxidation of single layer electrenes (O/${A}_{2}B$), and two side oxidation of bilayer electrenes (O/${({A}_{2}B)}_{2}$/O). We show that the hexagonal lattice of the pristine host is no longer the ground state structure in the (fully) oxidized systems. Our total energy results reveal an exothermic structural transition from hexagonal to tetragonal ($\mathrm{h}\ensuremath{\rightarrow}\mathrm{t}$) geometry, resulting in layered tetragonal structures [(${A\mathrm{O}AB)}^{\mathrm{t}}$ and ${(A\text{O}{(AB)}_{2}A\text{O})}^{\mathrm{t}}$]. Phonon spectra calculations and molecular dynamic simulations show that the O/${A}_{2}B$ and O/${({A}_{2}B)}_{2}$/O systems, with $A$ = Ba, Ca, Sr, and $B$ = N, become dynamically and structurally stable upon such a $\mathrm{h}\ensuremath{\rightarrow}\mathrm{t}$ transition. Further structural characterizations were performed based on simulations of the near edge x-ray absorption spectroscopy at the nitrogen $K$ edge. Finally, the electronic band structure and transport calculations reveal the formation of half-metallic bands spreading out through the $A\mathrm{N}$ layers, which in turn are shielded by oxide $A\mathrm{O}$ sheets. These findings indicate that ($A\mathrm{O}A\mathrm{N}$)${}^{\mathrm{t}}$ and ${(A\mathrm{O}{(A\mathrm{N})}_{2}A\mathrm{O})}^{\mathrm{t}}$ are quite interesting platforms for application in spintronics; since the half-metallic channels along the $A\mathrm{N}$ or ${(A\text{N})}_{2}$ layers (core) are protected against the environment conditions by the oxidized $A\text{O}$ sheets (cover shells).

Orbital localization and the role of the Fe and As 4p orbitals in BaFe2As2 probed by XANES

The polarization dependence of the near edge x-ray absorption spectroscopy (XANES) is an element specific probe to the real-space distribution of the density of unoccupied states in solid-state materials. In this paper, we present Fe and As $K$-edge experiments of Ba(Fe$_{1-x}$$M_{x}$)$_{2}$As$_{2}$ ($M=$ Mn, Co and $x=0.0$ and $0.08$). The experiments reveal a strong polarization dependence of the probed XANES spectra, which concerns mainly an increase of the intensity of electronic transitions when the beam polarization is set out of the sample's $ab$ crystallographic plane. The results show that states with $p_{z}$-orbital character dominate the density of unoccupied states close to the Fermi level. Partial substitution of Fe by Co is shown to decrease the intensity anisotropy, suggesting that Co promotes electronic transfer preferentially to states with $p_{z}$-orbital character. On the other hand, Mn substitution causes the increase of the spectra $p_{z}$-orbital anisotropy, which is proposed to take place by means of an enhanced local Fe $3d4p$ mixing, unveiling the role of Fe $4p$ states in the localization of the Fe $3d$ orbitals. Moreover, by comparing our results to previous experiments, we identify the relative mixing between Fe and the pnictide $4p_{x,y,z}$ orbitals as a clear divide between the electronic properties of iron arsenides and selenides. Our conclusions are supported by multiple-scattering theory calculations of the XANES spectra and by quantum chemistry calculations of Fe coordination electronic structure.

Covalency between the uranyl ion and dithiophosphinate by sulfur K-edge X-ray absorption spectroscopy and density functional theory.

The dithiophosphinic acids (HS2PR2) have been used for the selective separation of trivalent actinides (AnIII) from lanthanides (LnIII) over the past decades. The substituents on the dithiophosphinic acids dramatically impact the separation performance, but the mechanism is still open for debate. In this work, two dithiophosphinic acids with significantly different AnIII/LnIII separation performance, i.e. diphenyl dithiophosphinic acid (HS2PPh2) and bis(ortho-trifluoromethylphenyl) dithiophosphinic acid [HS2P(o-CF3C6H4)2], are employed to understand the substituent effect on the bonding covalency between the S2PR2- anions (R = Ph and o-CF3C6H4) and the uranyl ion by sulfur K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory calculations. The two UO2(S2PR2)(EtOH) complexes display similar XAS spectra, in which the first pre-edge feature with an intensity of 0.16 is entirely attributed to the transitions from S 1s orbitals to the unoccupied molecular orbitals due to the mixing between U 5f and S 3p orbitals. The Mulliken population analysis indicates that the amount of \% S 3p character inthese orbitals is essentially identical for the UO2(S2PPh2)2(EtOH) and UO2[S2P(o-CF3C6H4)2]2(EtOH) complexes, which is lower than that in the U 6d-based orbitals. The essentially identical covalency in U-S bonds for the two UO2(S2PR2)2(EtOH) complexes are contradictory to the significantly different AnIII/LnIII separation performance of the two dithiophosphinic acids, thus the covalency seems to be unable to account for substituent effects in the AnIII/LnIII separation by the dithiophosphinic acids. The results in this work provide valuable insight into the understanding of the mechanism in the AnIII/LnIII separation by the dithiophosphinic acids.

Interfacial electronic properties of FeTPP-Cl on HOPG

Conjugated tetrapyrrole complexes have potential for novel spintronic and optoelectronic devices. Detailed understanding of electronic properties at molecule–substrate interface is essential for their potential applications. In this report, electronic properties of iron (III) chloride tetraphenylporphyrin (FeTPP-Cl, C44H28ClFeN4) thin films on highly oriented pyrolytic graphite (HOPG) have been investigated using photoemission and X-ray absorption spectroscopy. Photoemission analysis shows that no significant charge transfer takes between FeTPP-Cl and HOPG. Fe 2P3/2 core level analysis indicates towards dechlorination of FeTPP-Cl on HOPG in the monolayer regime. Fe L2,3 edge X-ray absorption spectroscopy reveal that iron oxidation state changes from +2 to +3 due to adsorption on to HOPG, suggesting a substrate driven dechlorination of FeTPP-Cl. Curve fitting analysis of XPS Fe 2p3/2 spectrum for the deposition of FeTPP-Cl on HOPG in the monolayer regime confirms +2 oxidation state of central metal atom. An interface dipole of 0.2 eV has been found at FeTPP-Cl/HOPG interface suggesting weaker molecule–substrate interactions.

Revisiting properties of CaCoSinO2n+2. Crystal and electronic structure

In a public space there are several reports of materials with general stoichiometry CaCoSinO2n+2. Pyroxene CaCoSi2O6 is probably the best-known representative for n = 2 but not much is known about materials with n = 3 and n = 4. In this study, attempts were carried out to synthesize those phantom materials and it was found that they do not exist as a single phase. A quantitative XRD analysis revealed that their chemical composition is correct but the formula should be written as CaCoSi2O6 + (n-2)SiO2. Similar qualitative conclusions were drawn from investigation of magnetic (DC magnetometry) and electronic properties using X-ray Photoelectron Spectroscopy (XPS) and Si K edge X-ray Absorption Spectroscopy (XAS). Additionally, the DFT ab initio calculations were carried out to obtain electronic signature from band structure of CaCoSi2O6.The apparent influence of the excess of SiO2 on magnetic properties of this “series” can be understood in terms of presence and suppression of secondary phases like Ca2CoSi2O7, which form when the starting materials are not homogenized properly. Addition of surplus SiO2 suppresses their formation leaving clear signature from CaCoSi2O6, which also can be synthesized from stoichiometric mixture using proper techniques.