X-ray Absorption Measurements Research Articles

Operando double-edge high-resolution X-ray absorption spectroscopy study of BiVO4 photoanodes.

High energy resolution fluorescence detected X-ray absorption spectroscopy is a powerful method for probing the electronic structure of functional materials. The X-ray penetration depth and photon-in/photon-out nature of the method allow operando experiments to be performed, in particular in electrochemical cells. Here, operando high-resolution X-ray absorption measurements of a BiVO4 photoanode are reported, simultaneously probing the local electronic states of both cations. Small but significant variations of the spectral lineshapes induced by the applied potential were observed and an explanation in terms of the occupation of electronic states at or near the band edges is proposed.

A versatile beamline for soft x-ray reflectivity, absorption, and fluorescence measurements at Indus-2 synchrotron source.

A versatile beamline for performing reflectivity, fluorescence, and absorption experiments in the soft x-ray region of 100-1500eV is commissioned on a bending magnet port of the Indus-2 synchrotron source. A high vacuum 2-axis reflectometer with x, y, and z sample scanning stages is installed. This reflectometer is used to measure the reflectivity of large samples up to 300mm in length and 5kg in weight. This feature is useful for characterizing x-ray optical elements, such as mirrors, gratings, and multilayers. A flange mounted silicon drift detector is installed in the downstream of the reflectometer for soft x-ray fluorescence measurements. The soft x-ray absorption measurements are carried out in the total electron yield and partial fluorescence yield modes. Integration of three different experimental techniques in the experimental station makes the beamline versatile for materials science applications as it provides structural, chemical, and electronic state information by performing the required experiments in an identical environment. The beamline uses a varied line spacing plane grating monochromator and gives a high flux (∼109 to 1011 photon/s) with a moderate resolution (λ/Δλ ~1000-5000). A three-mirror-based higher harmonic setup is incorporated to get rid of harmonics and to get a high spectral purity monochromatic beam with less than 0.1% harmonic content. In the present article, the beamline optical scheme, mechanical configuration, and details of the experimental setups are presented, along with a few representative results of each experimental mode.

Structural studies of Prussian Blue Analogs containing trivalent hexacyanoferrate by extended X-ray absorption fine structure spectroscopy

The structure of 10 Prussian Blue Analogs containing trivalent hexacyanoferrate was investigated by extended X-ray absorption fine structure spectroscopy at the Fe 1 s edge and the transition metal 1 s edges. Despite the changes in physical properties due to differences in the non-iron transition metal and the interatomic distance between Fe and the non-iron transition metal, there was almost no change in the structure of trivalent hexacyanoferrate ions. Although this result agrees with the conclusions of many previous structural analyses, it raises a new question compared to our previous research conducted soft X-ray absorption measurements at the Fe 2p edge, which states that the detailed electronic state of Fe varies in proportion to the interatomic distance between Fe and the non-iron transition metal.

Li2s-PI3 Cathode for High-Energy-Density All-Solid-State Lithium-Sulfur Batteries

1.Introduction All-solid-state lithium-sulfur batteries (ASSLSBs) are one of the most promising next-generation large scale energy storage devices due to their remarkably high theoretical energy density, which is generated by high capacity of both cathodes, like element S or Li2S and Li metal anode. However, due to insufficient electronic and/or ionic conductivities of element S and Li2S, the low sulfur utilization and correspondingly unsatisfied practical energy density hinder the application of ASSLSBs largely. By heterovalent doping, vacancies in Li2S could be created, leading to higher ionic conductivity [1-2]. In this study, we developed different proportion of PI3-doping Li2S as active material to improve the sulfur utilization. Mixing with CNovel as electronic additive, Li2S-PI3-CNovel as cathode material shows good electrochemical performance. In order to clarify the effect of doping PI3, a detailed analysis of the point defect structure was performed using pair distribution function analysis using high-energy X-ray diffraction, synchrotron X-ray diffraction measurements, and X-ray absorption measurements to correlate with the electrochemical properties. 2. Experimental Li2S-PI3 as active material was synthesized by mixing Li2S and PI3 as raw materials with ball milling method and the proportion of raw materials has been optimized. The characterization of the prepared Li2S-PI3 was conducted by Synchrotron XRD coupled with pair Distribution Function analysis. The ionic conductivities were measured by AC impedance. The cathode materials were prepared based on active materials (90 wt%) and CNovel (10 wt%) as electronic conductor. The batteries composed of Li2S-PI3-CNovel as cathode, Li3PS4 as SSE and Li-In alloy as anode were assembled in the glove box filled with Ar atmosphere. The charge-discharge curves were obtained by galvanostatic measurement. The electronic structure and morphology of the Li2S-PI3-CNovel after electrochemical measurements were examined by X-ray Absorption Spectroscopy (XAS) for S K-edge, P K-edge, and I K-edge. 3.Results and Discussion Pair distribution function (PDF) analysis revealed that with PI3 doping, iodine atoms would occupy sulfur sites and phosphorous atoms would occupy lithium sites, creating lithium vacancies in the antifluorite structure. Figure 1 shows the charge/discharge curves of the Li2S-PI3-CNovel as cathode. The Li2S-PI3-CNovel cathode shows a charge capacity of 440 mAh g-1 and a discharge capacity of 494 mAh g-1 in the first cycle. And the capacities increase to 538 mAh g-1 during the subsequent cycles, with an average voltage of 1.81 V (vs Li/Li+). Even at 1 C (1 C=626 mAh g-1), the cathode without solid-state electrolyte could deliver 207 mAh g-1, corresponding to 38 % capacity retention of that at 0.05 C, which demonstrates good rate performance (Figure 2). The charge compensation is attributed to S, suggesting the conversion reaction between Li2S and element S, which was confirmed by XAS for S K-edge and P K-edge. References H Gamo.et al., Adv. 2022, 3, 2488-2494.NHH Phuc. et al., Energy Res., 2021, 8, 606023. Acknowledgement This research was financially supported by JST ALCA-SPRING Project. Figure 1

Atomically dispersed zeolite-supported rhodium complex: Selective and stable catalyst for acetylene semi-hydrogenation

Supported rhodium catalysts are known to be unselective for semi-hydrogenation reactions. Here, by tuning the electronic structure of supported mononuclear rhodium sites determined by the metal nuclearity and the electron-donor properties of the support, we report that atomically dispersed HY zeolite-supported rhodium with reactive acetylene ligands affords a stable ethylene selectivity > 90 % for acetylene semi-hydrogenation at 373 K and atmospheric pressure, even when ethylene is present in a large excess over acetylene. Infrared and X-ray absorption spectra and measurements of rates of the catalytic reaction complemented with calculations at the level of density functional theory show how the catalyst performance depends on the electronic structure of the rhodium, influenced by the support as a ligand that is a weak electron donor.

Disentangling the evolution of electrons and holes in photoexcited ZnO nanoparticles

The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy, and ab initio molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The x-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the x-ray absorption signal is found to rise in ∼1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of ∼100 cm−1, which corresponds to a phonon mode of the system involving the Zn sub-lattice.

Understanding Polymer Structure and Conductivity in Composite Electrolytes

Lithium ion batteries are a crucial technologies for electric vehicles and portable electronics due to their high energy density. However, flammable liquid electrolytes create a safety concern and transitioning to all solid state batteries allows for the potential of higher energy density by utilizing lithium metal anodes. Two classes of solid materials have been explored to replace liquid electrolytes: ceramic and polymer electrolytes. Composite electrolytes, typically in the form of dispersed ceramic particles or nanowires in polymer matrix, combine these two materials to have good ionic conductivity while maintaining the mechanical properties of the polymer. While they have achieved fairly high conductivity (typically 10-4 S/cm), the mechanism for such ion conduction is not well understood.The polymer likely plays a crucial role as the ceramic volume fractions are typically under 20%.1,2 Four possible ways that polymers could increase in conductivity in the composite have been identified: decreased crystallinity, increased free volume, disruption of polymer alignment, and increased lithium ion dissolution due to acidic surface groups on the ceramic.1,3,4 We have developed thin film model systems to probe the interface of the polymer with and ceramic surfaces. We found that when confined to thin films, the conductivity of the polymer electrolyte increased compared to the bulk. We utilized differential scanning calorimetry to identify the crystallinity and found that the small crystallinity variation could not account for the variation in conductivity. Subsequently, we utilized surface conductivity and transference number measurements to understand the effects of acidic surface groups. X-ray Absorption measurements will be similarly utilized to probe the variation in lithium ion environments within these materials to understand any variation in the lithium salt dissolution. It was found that the variation in conductivity based on this effect is small.In order to probe the possible variation in free volume, Small Angle Neutron Scattering will be utilized to quantify the free volume within thin films, bulk polymer, and composite electrolytes. This can quantify the volume associated with each monomer and therefore how much space is between polymer chains for lithium ion movement.5 Lastly, while the polymer chain alignment has not been extensively discussed composite literature, it has been identified that when polymer electrolytes are cast on a surface, polymer electrolytes typically show anisotropy with measurements parallel to the surface having higher conductivity due to the alignment of the chain.6 Therefore, ceramic fillers in the composites may disrupt this packing and allow for higher conductivity perpendicular to the cast surface, the direction in which they are most commonly measured. In order to probe this effect, we measure the anisotropy of both our thin film electrolytes as well as composite electrolytes to compare the significance of the anisotropy and utilize small angle x-ray scattering to measure any anisotropy in the structure.

Bonding wire characterization using non-destructive X-ray imaging

Counterfeiting in the semiconductor industry poses a significant threat to the economy and can lead to lower performance and reliability of electronic devices. X-ray technology in this respect is commonly used for non-destructive testing to identify physical defects and anomalies in integrated circuits. However, for accurate material identification, destructive methods such as spectroscopic techniques including X-ray diffraction and X-ray fluorescence are typically required. In this work, a fast and non-destructive method is presented for material characterization of bonding wires in ICs and other SMD components by measuring X-ray absorption profiles. The results demonstrated that the X-ray imaging technique can effectively distinguish between bonding wires made of gold, silver, copper, and aluminum. Moreover, the thickness of these materials can also be detected. This technique exhibits high potential for utilization as a simple and quick method for non-destructive material characterization in the industrial environment.

Modification of Optical System for Improving Measurement Precision and Sensitivity of a Laboratory-type X-ray Absorption Spectrometer and Measurement of Battery Material Metal Elements

Modification of Optical System for Improving Measurement Precision and Sensitivity of a Laboratory-type X-ray Absorption Spectrometer and Measurement of Battery Material Metal Elements

FlexPES: a versatile soft X-ray beamline at MAX IV Laboratory.

FlexPES is a soft X-ray beamline on the 1.5 GeV storage ring at MAX IV Laboratory, Sweden, providing horizontally polarized radiation in the 40-1500 eV photon energy range and specializing in high-resolution photoelectron spectroscopy, fast X-ray absorption spectroscopy and electron-ion/ion-ion coincidence techniques. The beamline is split into two branches currently serving three endstations, with a possibility of adding a fourth station at a free port. The refocusing optics provides two focal points on each branch, and enables either focused or defocused beam on the sample. The endstation EA01 at branch A (Surface and Materials Science) is dedicated to surface- and materials-science experiments on solid samples at ultra-high vacuum. It is well suited not only to all flavours of photoelectron spectroscopy but also to fast (down to sub-minute) high-resolution X-ray absorption measurements with various detectors. Branch B (Low-Density Matter Science) has the possibility to study gas-phase/liquid samples at elevated pressures. The first endstation of this branch, EB01, is a mobile setup for various ion-ion and electron-ion coincidence techniques. It houses a versatile reaction microscope, which can be used for experiments during single-bunch or multi-bunch delivery. The second endstation, EB02, is based on a rotatable chamber with an electron spectrometer for photoelectron spectroscopy studies on primarily volatile targets, and a number of peripheral setups for sample delivery, such as molecular/cluster beams, metal/semiconductor nanoparticle beams and liquid jets. This station can also be used for non-UHV photoemission studies on solid samples. In this paper, the optical layout and the present performance of the beamline and all its endstations are reported.

Size and Composition Control of Magnetic Nanoparticles

Magnetite nanoparticles are a type of magnetic nanoparticle (MNP) that are inexpensive to make and can be formed in different shapes and sizes. MNPs can be used in DNA/RNA purification, drug delivery, and other biomedical applications. The commonly employed solvothermal route to make these MNPs gives the most uniform products with the smallest size distribution, but there is a need to identify easily controlled changes to reaction parameters that can reliably tune the size and composition of the MNPs made by this method. In this work we report simple and reliable methods whereby adjusting the total water content and basic salt concentration affords size and composition control, respectively. We employ synchrotron X-ray absorption measurements to prove our method offers monotonic control over MNP composition from maghemite-rich (γ-Fe2O3) to the more magnetic magnetite (Fe3O4). This demonstrates a simple, general method to produce particles with high magnetite concentration and the desired size.

Oxide Coating Role on the Bulk Structural Stability of Active LiMn2O4 Cathodes.

The protective coating of the electrode materials is a known source of improvement of the cycling performances in battery devices. In the case of the LiMn2O4 cathodes, the coating with a thin alumina layer has been proven to show performance efficiency. However, the precise mechanism of its effect on the performance improvement of the electrodes is still not clear. In this work we investigate alumina-coating-induced effects on the structural dynamics of the active materials in correlation to the modified solid electrolyte interface dynamics. The local structures of coated and uncoated samples at different galvanostatic points are studied by both soft X-ray absorption measurements at the Mn L-edges and O K-edge (in total electron yield mode) and hard X-ray absorption at the Mn K-edge (in transmission mode). The different probing depths of the employed techniques allowed us to study the structural dynamics both at the surface and within the bulk of the active material. We demonstrate that the coating successfully hinders the Mn3+ disproportionation and, hence, the degradation of the active material. Side products (layered Li2MnO3 and MnO) and changes in the local crystal symmetry with formation of Li2Mn2O4 are observed in uncoated electrodes. The role of alumina coating on the stability of the passivation layer and its consequent effect on the structural stability of the bulk active materials is discussed.

Mass absorption coefficient in the 200-800eV region of sp3 carbon atoms measured using self-standing polyethylene thin films.

To experimentally determine the mass absorption coefficient (μ) of a sp3-carbon (C) atom in the soft X-ray region, soft X-ray absorption spectra (XAS) in the 200-800eV and C K regions of 200-nm-thick self-standing polyethylene (PE) films were measured in the transmission and total electron yield (TEY) modes. PE films were prepared by a spin-coating method. Their experimentally measured thickness and density are 200nm and 0.920g/cm3, respectively. Soft X-ray absorption measurements were performed in beamline BL-6.3.2 at the Advanced Light Source. Although surface oxygen can be slightly observed in the O K and C K regions in TEY-XAS, it cannot be observed in absorbance-XAS. The absorbance-XAS profiles agree well with the calculated profiles, except in the C K threshold. Hence, it can be confirmed that the absorption-XAS measurements are achieved. From the absorbance, μ of sp3-C in PE is 7 × 104 cm2/g near 288eV and 294eV.

Cover Feature: PdCl(NO) – an iconic compound with corrugated Pd4Cl4 octagons built up by Pd2Cl2(NO)2 moieties (Z. Anorg. Allg. Chem. 6‐7/2023)

The cover picture presents a structural motif of a distorted Pd2Cl2 square in solid PdCl(NO). This iconic compound was firstly synthesized during outstanding research in the late 1950s in Munich, which led to the development of the Wacker process for the conversion of ethene into acetaldehyde by catalysis with PdCl2. More than sixty years after its synthesis, crystals of PdCl(NO) were prepared for the first time and the structure determined by X-ray diffraction. In the monoclinic structure distorted Pd4Cl4 octagons in chair arrangement are interconnected to corrugated layers, forming a two-dimensional polymer insoluble in common solvents. In this compound each Pd atom is connected to a N-O group, bonded alternatively up and down with a Pd-N-O angle of 129°. The bonding situation in PdCl(NO) was investigated by vibrational, electronic and X-ray absorption (XAS) spectroscopies. The XAS measurement at the KIT synchrotron facility uncovers that the charge located at the Pd atom in PdCl(NO) is comparable to that in PdCl2 or PdO (DOI: 10.1002/zaac.202200337).

Fabrication and Properties of Epitaxial VO2 Thin Film on m-Al2O3 Substrate

A thin film of thermochromic VO2 was prepared on m-Al2O3 substrate using a radio frequency (RF) magnetron sputtering technique. The epitaxial growth of the monoclinic M1 phase of VO2 on the m-Al2O3 substrate was confirmed through synchrotron X-ray diffraction (XRD) measurements. The transformation of this monoclinic M1 phase into a rutile phase at ~68 °C was reflected in the temperature-dependent XRD measurements of the VO2 thin film. The temperature-dependent electrical resistance measurements of this sample also revealed an abrupt metal-to-insulator transition at ~68 °C, which is reversible in nature. Temperature-dependent X-ray absorption (XAS) measurements at V L-edge and O K-edge were performed to study the electronic structure of the epitaxial VO2/m-Al2O3 thin film during the metal-to-insulator (MIT) transition.

Evidence of symmetry breaking in a Gd2 di-nuclear molecular polymer.

A chiral 3D coordination compound, [Gd2(L)2(ox)2(H2O)2], arranged around a dinuclear Gd unit has been characterized by X-ray photoemission and X-ray absorption measurements in the context of density functional theory studies. Core level photoemission of the Gd 5p multiplet splittings indicates that spin orbit coupling dominates over j-J coupling evident in the 5p core level spectra of Gd metal. Indications of spin-orbit coupling are consistent with the absence of inversion symmetry due to the ligand field. Density functional theory predicts antiferromagnet alignment of the Gd2 dimers and a band gap of the compound consistent with optical absorption.

Growth and electronic properties of Co-doped Mn3O4 thin films: a combined experimental and theoretical investigation.

In this study, we have prepared and investigated the electronic properties of a new and promising cobalt doped Mn3O4 oxide surface by site-selective and element-sensitive X-ray-absorption (XAS) and photoemission spectroscopy (XPS and resonant PES) combined with density functional theory (DFT) calculations. The crystallinity of both pristine and Co doped thin films was ensured by low energy electron diffraction measurements, in which similar diffraction patterns were obtained for both films suggesting the inclusion of the dopant species within the crystalline Mn3O4 thin film. According to our combined experimental data and theoretical calculation results, XAS measurements and replace energy calculations could identify Co impurities adopting preferentially a 2+ oxidation state substituting a Mn2+ cation on tetrahedral sites (80%) as well as the Mn3+ on octahedral sites (20%). Direct evidence of these findings could be found by comparing the pristine Mn3O4 electron absorption and photoemission spectral features with those of the doped ones. For instance, the formation of oxygen vacancies related to the formation of Co2+ in an octahedral site could be directly observed. Remarkably, the valence band spectrum of Co-Mn3O4 thin films presents additional spectral features close to the Fermi edge that can be directly attributed to Co states when compared to the PDOS obtained by the DFT calculations. It is noteworthy that the formation and stabilization of these Co dopant species in the host Mn3O4 surface could potentially affect and obviously modulate its capability for adsorption of molecular species and transfer of electrons, which makes the cobalt doped Mn3O4 surface potentially promising for catalytic applications.

Titanium and titanium oxides at the K- and L-edges: comparing theoretical calculations to X-ray absorption and X-ray emission measurements

Using well-calibrated experimental data we demonstrate the applicability of theoretical XAS and XES calculations for Ti, TiO, and TiO2 at the Ti K and L edges as well as O K edge.

Highly selective CO2 electrocatalytic reduction on nickel single-atom catalyst in a high-temperature shockwave method

Recently, the easily prepared catalysis used in CO2 electrochemical reduction with high selectivity and low cost has attracted more and more attention. Compared with the temperate wet chemical preparation method, which takes a long time and introduces some impurities, we found nickel metal catalysts can be easily and quickly synthesized on carbon black using the high-temperature shockwave method, which has the advantages of rapid heating up to 1300–1500 K within 0.5 s, no introduction of excess elements and extreme low unfavorable nitrogen dopants. Heating cycles and proportion of nitrogen source have been investigated on the catalyst morphology, particle size and electrocatalysis performance. Based on operando X-ray absorption and aberration-corrected scanning transmission electron microscopy (STEM) measurements, nickel single atom catalysts (Ni SACs) were prepared successfully and uniformly in modest heating cycles and proportion of nitrogen source. The Ni SACs exhibited remarkable performance in reducing carbon dioxide (CO2) to carbon monoxide (CO), with the current density of 27.5 mA/cm2 (−1.0 V vs reversible hydrogen electrode) and CO selectivity approaching 100 % in flow cell.

Perturbing the spin state and conduction of Fe (II) spin crossover complexes with TCNQ

We investigated modifications driven by 7,7,8,8-tetracyanoquinodimethane (TCNQ) to the spin state configuration of [Fe(3-bpp)2](TCNQ)2 co-crystal and both spin state and electric conductivity of [Fe{H2B(pz)2}2(bipy)] and TCNQ mixtures. The Fe2+ site in the [Fe(3-bpp)2](TCNQ)2 co-crystal has a sizable orbital moment. During X-ray absorption measurements, the iron ion is partially excited to the high spin state and strong surface effects are indicated. Mixing TCNQ with the [Fe{H2B(pz)2}2(bipy)] spin crossover complex leads to a molecular combination with increased conductivity and drift carrier lifetimes. [Fe{H2B(pz)2}2(bipy)] thin films with TCNQ, grown using dimethylformamide (DMF), are to great extent locked mainly in the low spin (LS) state across a broad temperature range and exhibit drift carrier lifetimes approaching 0.5 s. When deposited onto a ferroelectric polyvinylidenefluoride-hexafluoropropylene thin film substrate, [Fe{H2B(pz)2}2(bipy)], shows enhanced transistor carrier mobility, likely associated with the increasing cationic character of [Fe{H2B(pz)2}2(bipy)] thin films with TCNQ.