Partial Fluorescence Yield Research Articles

A high-energy-resolution resonant inelastic X-ray scattering spectrometer at ID20 of the European Synchrotron Radiation Facility.

An end-station for resonant inelastic X-ray scattering and (resonant) X-ray emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high-energy-resolution applications, including partial fluorescence yield or high-energy-resolution fluorescence detected X-ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non-resonant inelastic X-ray scattering measurements of valence electron excitations.

Quantification of Olivine Using Fe Lα in Electron Probe Microanalysis (EPMA).

Quantification of first series transition metal Lα X-rays is hampered by absorption and in some cases transition probabilities (fluorescence yields) varying with chemical bonding. Compound mass absorption coefficients for Fe Lα were measured in the olivine solid solution series [Forsterite (Mg2SiO4) to Fayalite (Fe2SiO4)] and the mass absorption coefficients for Fe Lα absorbed by Fe were calculated. The mass absorption coefficients vary systematically between Fo83 and Fo0. Using the measured mass absorption coefficients for both standard and unknown and by correcting for a systematic discrepancy, consistent with varying partial fluorescence yields, a good agreement between calculated k-ratios and measured k-ratios is achieved. The systematic variations allow quantification of unknown k-ratios. The described method of quantification requires modification of matrix correction routines to allow standards and unknowns to have different mass absorption coefficients, and to incorporate solid solution mass absorption coefficients and partial fluorescence yield corrections derived from regression of experimental data.

The surface chemistry of metallurgical aluminas

We have studied the evolution of surface basicity as a function of calcination temperature in a range of transition alumina‐rich analogues of metallurgical grade aluminas produced by calcination of Bayer gibbsite. Specific basicity, the number of basic sites per unit surface area, was determined by thermometric back‐titration and found to increase with calcination temperature up to ~700°C to 800°C, decreasing dramatically thereafter. The population of tetrahedrally coordinated Al3+, which exhibits a qualitatively similar evolution, was determined by Al K‐edge near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy but found not to correlate with basicity changes. Interestingly, a shift to higher and then lower binding energy of Al 2p photoelectrons by X‐ray photoelectron spectroscopy and changes in the intensity of O K‐edge NEXAFS spectra do appear to correlate with surface basicity. Exploiting the differing surface sensitivities of NEXAFS spectra collected in partial electron and total fluorescence yield modes, we find O K‐edge spectra intensities, Al 2p X‐ray photoelectron spectrometer binding energies, and surface basicity all reflect the reorganisation of internal surfaces rather than changes in AlO4:AlO6 occupation. Copyright © 2017 John Wiley & Sons, Ltd.

Estimation of Ce 4f–5d Interaction by Analysis of Partial Fluorescence Yield at the Ce L3 Edge of CeO2

Partial fluorescence yield (PFY) spectroscopy, which corresponds to a high-resolution version of the X-ray absorption spectroscopy (XAS), is experimentally performed at the Ce L3 edge of CeO2, and the result is theoretically analyzed using an impurity Anderson model (IAM). In order to estimate the Ce 4f–5d interaction Ufd, we employ a semi-empirical IAM framework based on the local density approximation+U method; Slater–Koster parameters describing the valence of CeO2 are estimated by band mapping within the linear combination of atomic orbitals scheme, and the resulting realistic valence structure is considered in the IAM analysis. The global structure of the PFY-XAS result, which consists of the Ce 2p3/2 → 5d dipole transition and the Ce 2p3/2 → 4f quadrupole transition, is excellently reproduced by the calculation. The Ufd value is estimated to be 3.0 eV. We emphasize that the sensitivity of PFY-XAS to Ufd makes it a good ruler for obtaining the Ufd values of Ce compounds.

Redox Processes of Manganese Oxide in Catalyzing Oxygen Evolution and Reduction: An in Situ Soft X-ray Absorption Spectroscopy Study

Manganese oxides with rich redox chemistry have been widely used in (electro)catalysis in applications of energy and environmental consequence. While they are ubiquitous in catalyzing the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), redox processes occurring on the surface of manganese oxides are poorly understood. We report valence changes at OER- and ORR-relevant voltages of a layered manganese oxide film prepared by electrodeposition. X-ray absorption spectra were collected in situ in O2-saturated 0.1 M KOH using inverse partial fluorescence yield (IPFY) at the Mn L3,2-edges and partial fluorescence yield (PFY) at the O K-edge. Overall, we found reversible yet hysteretic Mn redox and qualitatively reproducible spectral changes by Mn L3,2 IPFY XAS. Oxidation to a mixed Mn3+/4+ valence preceded the oxygen evolution at 1.65 V vs RHE, while manganese reduced below Mn3+ and contained tetrahedral Mn2+ during oxygen reduction at 0.5 V vs RHE. Analysis of the pre-edge in O K-edge XAS pr...

Characterization of the magnetic moments of ultrathin Fe film in an external electric field via high-precision X-ray magnetic circular dichroism spectroscopy

The magnetic moments of a Pt|Fe(0.5 nm)|MgO film at an external electric field of in a 0.35 V/nm were characterized by analyzing the X-ray magnetic circular dichroism (XMCD) at the L-edges of Fe using a partial fluorescence yield method with a precision 40 times greater than that in our previous study. The XMCD induced by the electric field was negligible (<0.2%). Furthermore, although an induced orbital magnetic moment seemingly existed, it was within the precision error (0.3%). This paper demonstrates that slight electron doping and/or redistribution without any electrochemical reaction causes voltage-controlled magnetic anisotropy at Fe|MgO interfaces.

Capturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic circular dichroism

Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant x-ray scattering at a beamline BL07LSU in SPring-8 with a time-resolution of under 50 ps are presented. A micro-channel plate is utilized for the Tr-XMCD measurements at nearly normal incidence in both the partial electron and total fluorescence yield (PEY and TFY) modes at the L2,3 absorption edges of the 3d transition-metals in the soft x-ray region. The ultrafast photo-induced demagnetization within 50 ps is observed on the dynamics of a magnetic material of FePt thin films, having a distinct threshold of the photon density. The spectrum in the PEY mode is less-distorted at both the L2,3 edges compared with that in the TFY mode and has the potential to apply the sum rule analysis for XMCD spectra in pump-probed experiments.

High-efficiency in situ resonant inelastic x-ray scattering (iRIXS) endstation at the Advanced Light Source.

An endstation with two high-efficiency soft x-ray spectrographs was developed at Beamline 8.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory. The endstation is capable of performing soft x-ray absorption spectroscopy, emission spectroscopy, and, in particular, resonant inelastic soft x-ray scattering (RIXS). Two slit-less variable line-spacing grating spectrographs are installed at different detection geometries. The endstation covers the photon energy range from 80 to 1500 eV. For studying transition-metal oxides, the large detection energy window allows a simultaneous collection of x-ray emission spectra with energies ranging from the O K-edge to the Ni L-edge without moving any mechanical components. The record-high efficiency enables the recording of comprehensive two-dimensional RIXS maps with good statistics within a short acquisition time. By virtue of the large energy window and high throughput of the spectrographs, partial fluorescence yield and inverse partial fluorescence yield signals could be obtained for all transition metal L-edges including Mn. Moreover, the different geometries of these two spectrographs (parallel and perpendicular to the horizontal polarization of the beamline) provide contrasts in RIXS features with two different momentum transfers.

Soft X-ray spectroscopy of transition metal compounds: a theoretical perspective

To date, X-ray spectroscopy has become a routine tool that can reveal highly local and element-specific information on the electronic structure of atoms in complex environments. Here, we report on the development of an efficient and versatile theoretical methodology for the treatment of soft X-ray spectra of transition metal compounds based on the multi-configurational self-consistent field electronic structure theory. A special focus is put on the L-edge photon-in/photon-out and photon-in/electron-out processes, i.e. X-ray absorption, resonant inelastic scattering, partial fluorescence yield, and photoelectron spectroscopy, all treated on the same theoretical footing. The investigated systems range from small prototypical coordination compounds and catalysts to aggregates of biomolecules.

Electron Probe Microanalysis of Ni Silicides Using Ni-L X-Ray Lines.

We report electron probe microanalysis measurements on nickel silicides, Ni5Si2, Ni2Si, Ni3Si2, and NiSi, which were done in order to investigate anomalies that affect the analysis of such materials by using the Ni L3-M4,5 line (Lα). Possible sources of systematic discrepancies between experimental data and theoretical predictions of Ni L3-M4,5 k-ratios are examined, and special attention is paid to dependence of the Ni L3-M4,5 k-ratios on mass-attenuation coefficients and partial fluorescence yields. Self-absorption X-ray spectra and empirical mass-attenuation coefficients were obtained for the considered materials from X-ray emission spectra and relative X-ray intensity measurements, respectively. It is shown that calculated k-ratios with empirical mass attenuation coefficients and modified partial fluorescence yields give better agreement with experimental data, except at very low accelerating voltages. Alternatively, satisfactory agreement is also achieved by using the Ni L3-M1 line (Lℓ) instead of the Ni L3-M4,5 line.

X-Ray Absorption Spectroscopic Analysis of Cobalt-Doped Lithium Oxide Cathode Material for a Lithium-Peroxide Battery during Charge and Discharge

1. Introduction Recently, cathode materials using redox of oxide anion draw increasing attention for development of rechargeable batteries with high energy density. We have proposed a new rechargeable battery system using a redox between oxide and peroxide ions in a cathode material.1 The theoretical energy density is 2570 Wh/kg (voltage: 2.87 V, specific capacity: 897 mAh/g), assuming that the redox between Li2O and Li2O2. We have demonstrated that the battery system with Co-doped Li2O (CDL) as a cathode material exhibits a reversible capacity of 270 mAh/g operating on the redox of oxide and peroxide ions.1,2 But this obtained capacity is far less than the theoretical one. Therefore, there must be room for enhancing the specific capacity. For further improving the battery system, deeper knowledge and better understanding of charge/discharge mechanism of the CDL are required.X-ray absorption spectroscopy (XAS) is an effective method to investigate electronic states and coordination structures of elements of interest in a sample.1,3 In this study, we investigated the states of cobalt and oxygen in the CDL during charge and discharge by using both hard and soft XAS. 2. Experimental The CDL (Co/(Li+Co) = 0.09) was prepared from Li2O and LiCoO2 by using a planetary ball-mill.2 The CDL was mixed with acetylene black and polytetrafluoroethylene at a weight ratio of 75:20:5 or 85:10:5 to serve as cathodes. The cathode material pressed onto aluminum mesh, lithium metal as an anode, an electrolyte solution of 1 M LiBF4 dissolved in a mixture (1:1 by volume) of ethylene carbonate (EC) and diethyl carbonate (DEC), and a glass-fiber filter as a separator were assembled in a 2032 coin-type cell. All these procedures were operated in an argon-filled glove box.The cell was charged to 270 mAh/g and then discharged to 270 mAh/g at a current density of 4.5 mA/g at 298 K. The cathodes charged or discharged to various depths were removed from the cell, washed with EC-DEC once and with DEC twice, and dried under vacuum for XAS measurements.The hard XAS measurements at Co K-edge were carried out at the beam line BL9A of the Photon Factory in High Energy Accelerator Research Organization in a transmittance mode. The samples were packed in laminated aluminum foil bags. The soft XAS measurements at O K-edge were carried out at the beam line BL2 of Ritsumeikan University SR Center in both total electron yield (TEY) and partial fluorescence yield (PFY) modes. The samples were transferred to high-vacuum chamber of BL2 by using a transfer vessel filled with argon gas. 3. Results and discussion XAS spectra at Co K-edge were measured for the CDL charged and discharged in increments of 45 mAh/g. In the charge process, the absorption edge shifts to higher energy by 1.0 eV from 0 to 135 mAh/g and remains in almost the same position from 135 to 270 mAh/g. In the discharge process after charging to 270 mAh/g, the absorption edge gradually shifts to lower energy by 1.0 eV from 0 to 225 mAh/g and sharply shifts to lower energy by 1.3 eV from 225 to 270 mAh/g.XAS spectra at O K-edge were measured for the CDL charged and discharged in increments of 90 mAh/g. In the charge process from 0 to 90 mAh/g, a broad peak at 528 eV, which is attributed to electron transition from O 1s to Co 3d-O 2p hybridized states, increases in its intensity. In the charge process from 90 to 270 mAh/g, a new peak appears at 530 eV. This peak is attributed to peroxide in CDL since Li2O2 shows a peak attributed to electron transition from O 1s to σ*(O-O) at the same energy. In the discharge process, the peak at 530 eV weakens and disappears from 0 to 180 mAh/g and the broad peak at 528 eV decreases in its intensity from 180 to 270 mAh/g.These results suggest that the Co 3d-O 2p hybridized states contribute to charge transfer in the earlier charge period and the later discharge period. The formation and decomposition of peroxide species in the later charge period and the earlier discharge period, respectively, are spectroscopically traced, which are consistent with our previous results of chemical peroxide analysis.1 AcknowledgementsThis work was supported by JSPS Grant-in-Aid for Young Scientist (B) Grant Number 15K18326 and JSPS Grant-in-Aid for Scientific Researches (B) Grant Number 26289371. The XAS measurements were carried out under the approvals of the Photon Factory Program Advisory Committee (Proposal No. 2015G698).

Pressure dependence of the electronic structure of 4f and 3d electron systems studied by X-ray emission spectroscopy

ABSTRACTTechniques based on X-ray emission spectroscopy (XES) have been utilized to investigate pressure-induced changes in the electronic structure in samples subject to high pressure in the diamond anvil cell. High-resolution X-ray absorption spectra can be obtained with partial fluorescence yield mode (PFY-XAS) measurement. As typical examples, we show results of measurements of the valence fluctuating systems of CeCuGe, Ce115 systems, and YbNiGe. The pre-edge feature of the XAS spectra at K-absorption edge of 3d-elements correlates to the spin states. We also show the results of the Fe XES and PFY-XAS of KFeSe, which has two pressure-induced superconducting (SC) domes.

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Hard X-ray photoelectron spectroscopy (HAXPES) using an excitation energy range of 2keV to 6keV in combination with Fe K- and S K-edge XANES, measured simultaneously in total electron (TEY) and partial fluorescence yield (PFY) modes, have been applied to study near-surface regions of natural polycrystalline pyrite FeS2 and pyrrhotite Fe1−xS before and after etching treatments in an acidic ferric chloride solution. It was found that the following near-surface regions are formed owing to the preferential release of iron from oxidized metal sulfide lattices: (i) a thin, no more than 1–4nm in depth, outer layer containing polysulfide species, (ii) a layer exhibiting less pronounced stoichiometry deviations and low, if any, concentrations of polysulfide, the composition and dimensions of which vary for pyrite and pyrrhotite and depend on the chemical treatment, and (iii) an extended almost stoichiometric underlayer yielding modified TEY XANES spectra, probably, due to a higher content of defects. We suggest that the extended layered structure should heavily affect the near-surface electronic properties, and processes involving the surface and interfacial charge transfer.

Unraveling the Origin of Visible Light Capture by Core–Shell TiO2 Nanotubes

A black TiO2 nanotube (NT) heterostructure with an anatase-core and an amorphous-shell has been synthesized by NH3 annealing of amorphous NT grown by the anodization of a Ti substrate. Remarkable photoabsorption behavior of these black TiO2 NTs is observed: strong absorption throughout the entire optical wavelength region from ultraviolet to near-infrared. X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and resonant inelastic X-ray scattering (RIXS) have been used to elucidate the origin of this spectacular light capture phenomenon. Surface-sensitive XANES recorded in total electron yield and XPS show that the surface layer is amorphous with a chemical composition approaching that of Ti4O7. Bulk-sensitive XANES using X-ray partial fluorescence yield and Ti 2p RIXS confirm the presence of a rich amount of Ti3+ in the crystalline bulk (core of the NT with anatase structure) of black TiO2 NTs, which exhibits a dispersive d-d energy loss at ∼2 eV corresponding to the broad...

Undistorted X-ray Absorption Spectroscopy Using s-Core-Orbital Emissions.

Detection of secondary emissions, fluorescence yield (FY), or electron yield (EY), originating from the relaxation processes upon X-ray resonant absorption has been widely adopted for X-ray absorption spectroscopy (XAS) measurements when the primary absorption process cannot be probed directly in transmission mode. Various spectral distortion effects inherent in the relaxation processes and in the subsequent transportation of emitted particles (electron or photon) through the sample, however, undermine the proportionality of the emission signals to the X-ray absorption coefficient. In the present study, multiple radiative (FY) and nonradiative (EY) decay channels have been experimentally investigated on a model system, FeCl3 aqueous solution, at the excitation energy of the Fe L-edge. The systematic comparisons between the experimental spectra taken from various decay channels, as well as the comparison with the theoretically simulated Fe L-edge XA spectrum that involves only the absorption process, indicate that the detection of the Fe 3s → 2p partial fluorescence yield (PFY) gives rise to the true Fe L-edge XA spectrum. The two key characteristics generalized from this particular decay channel-zero orbital angular momentum (i.e., s orbital) and core-level emission-set a guideline for obtaining undistorted X-ray absorption spectra in the future.

Joint Analysis of Radiative and Non-Radiative Electronic Relaxation Upon X-ray Irradiation of Transition Metal Aqueous Solutions.

L-edge soft X-ray spectroscopy has been proven to be a powerful tool to unravel the peculiarities of electronic structure of transition metal compounds in solution. However, the X-ray absorption spectrum is often probed in the total or partial fluorescence yield modes, what leads to inherent distortions with respect to the true transmission spectrum. In the present work, we combine photon- and electron-yield experimental techniques with multi-reference first principles calculations. Exemplified for the prototypical FeCl2 aqueous solution we demonstrate that the partial yield arising from the Fe3s → 2p relaxation is a more reliable probe of the absorption spectrum than the Fe3d → 2p one. For the bonding-relevant 3d → 2p channel we further provide the basis for the joint analysis of resonant photoelectron and inelastic X-ray scattering spectra. Establishing the common energy reference allows to assign both spectra using the complementary information provided through electron-out and photon-out events.

Quantitative study of the f occupation in CeMIn5 and other cerium compounds with hard X-rays

We present bulk-sensitive hard X-ray photoelectron spectroscopy (HAXPES) data of the Ce3d core levels and lifetime-reduced L-edge X-ray absorption spectroscopy (XAS) in the partial fluorescence yield (PFY) mode of the CeMIn5 family with M=Co, Rh, and Ir. The HAXPES data are analyzed quantitatively with a combination of full multiplet and configuration interaction model which allows correcting for the strong plasmons in the CeMIn5 HAXPES data, and reliable weights wn of the different fn contributions in the ground state are determined. The CeMIn5 results are compared to HAXPES data of other heavy fermion compounds and a systematic decrease of the hybridization strength Veff from CePd3 to CeRh3B2 to CeRu2Si2 is observed, while it is smallest for the three CeMIn5 compounds. The f-occupation, however, increases in the same sequence and is close to one for the CeMIn5 family. The PFY-XAS data confirm an identical f-occupation in the three CeMIn5 compounds and a phenomenological fit to these PFY-XAS data combined with a configuration interaction model yields consistent results.

High pressure effects on U L3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd11

We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0–28.2 GPa) and single crystal x-ray diffraction (SXD) (0–20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K0 = 62(1) GPa and its pressure derivative, = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7.

We report measurements of the physical properties and electronic structure of the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical resistivity, magnetization, specific heat and partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly trivalent. Application of pressure to Yb2Ni12P7 suppresses TFL, the temperature below which Fermi liquid behavior is recovered, suggesting the presence of a quantum critical point (QCP) under pressure. However, while there is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong increase for Yb2Ni12As7 under pressure, before a near constant value is reached. These results indicate that any magnetic QCP in this system is well separated from strong valence fluctuations. The pressure dependence of the valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there is an anomaly in the unit cell volume as well as a change in the slope of the Yb valence, indicating a correlation between structural and electronic changes.

Effect of Pressure on Valence and Structural Properties of YbFe2Ge2 Heavy Fermion Compound--A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation.

The crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported.