Partial Fluorescence Yield Mode Research Articles

Pt-Mediated Interface Engineering Boosts the Oxygen Reduction Reaction Performance of Ni Hydroxide-Supported Pd Nanoparticles

Fuel cells are considered potential energy conversion devices for utopia; nevertheless, finding a highly efficacious and economical electrocatalyst for the oxygen reduction reaction (ORR) is of great interest. By keeping this in view, we have proposed a novel design of a trimetallic nanocatalyst (NC) comprising atomic Pt clusters at the heterogeneous Ni(OH)2-to-Pd interface (denoted NPP-70). The as-prepared material surpasses the commercial J.M.-Pt/C (20 wt %) catalyst by ∼ 166 and ∼19 times with exceptionally high specific and mass activities of 16.11 mA cm-2 and 484.8 mA mgPt-1 at 0.90 V versus reversible hydrogen electrode (RHE) in alkaline ORR (0.1 M KOH), respectively. On top of that, NPP-70 NC retains nearly 100% performance after 10k accelerated durability test (ADT) cycles. The results of physical characterization and electrochemical analysis confirm that atomic-scale Pt clusters induce strong lattice strain (compressive) at the Ni(OH)2-to-Pd interface, which triggers the electron relocation from Ni to Pt atoms. Such charge localization is vital for O2 splitting on surface Pt atoms, followed by the relocation of OH- ions from the Pd surface. Besides, a sharp fall down in ORR performance (mass activity is 37 mA mgPt-1 at 0.90 V versus RHE) is observed when the Pt clusters are decorated on the surface of NiOx and Pd (denoted NPP-RT). In situ partial fluorescence yield mode X-ray absorption spectroscopy (PFY-XAS) was employed to reveal the ORR pathways on both configurations. The obtained results demonstrate that interface engineering can be a potential approach to boost the electrocatalytic activity of metal hydroxide/oxide-supported Pd nanoparticles and in turn allow Pd to be a promising alternative for commercial Pt catalysts.

Sulfur in humin as a redox-active element for extracellular electron transfer

Humin (HM), an insoluble humic substance that occurs as an organo-mineral complex, mediates extracellular electron transfer (EET) among microorganisms in the geosphere. Although sulfur (S)-containing functional groups have been posited as possible redox-active groups in HM, there has been no direct evidence in this regard. Here, we characterized the redox-active S in HM from different natural sources using synchrotron radiation-based X-ray absorption spectroscopy in partial fluorescence yield mode. The S content in HM is less than 0.9%, with the oxidation states ranged widely from −2 to +6. About 9% to 19% of total S in HM was redox variable, corresponding to 1.2 × 10−5 to 17.1 × 10−5 Eq/g-HM redox capacity. The redox capacity of HM driven by S is comparable to or larger than the electron donating capacity of HM observed in anaerobic microbial dechlorination of pentachlorophenol, suggesting that S is one of the significant redox-active elements in HM. These findings provide new insights into the role of S cycling in biogeochemical processes and microbial energy networks.

Cu 2p-1s x-ray emission spectroscopy of mineral tetrahedrite Cu12Sb4S13

The electronic structure of mineral tetrahedrite Cu12Sb4S13 showing a metal-semiconductor transition (MST) at TMST = 85 K has been investigated by means of Cu 1s x-ray absorption spectroscopy with the partial fluorescence yield mode (PFY-XAS) and Cu 2p-1s x-ray emission spectroscopy (XES). Remarkable changes are detected in both the PFY-XAS and XES spectra on cooling across TMST. The changes in the spectra indicate that the unoccupied Cu 3d and 4p densities of states (DOS) shift away from the Fermi energy (EF). We conclude that the MST of Cu12Sb4S13 is associated with the decrease of the Cu 3d DOS at EF.

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.

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.

A new experiment station on beamline 4B7A at Beijing Synchrotron Radiation Facility

A new experiment station was installed on beamline 4B7A at Beijing Synchrotron Radiation Facility (BSRF), making it possible to record X-ray absorption fine structure (XAFS) spectrum in three modes over an energy range from 1750eV to 6000eV. A 13-element Si(Li) array detector and a single-element SDD detector were used to acquire data in partial fluorescence yield (PFY) mode. Two low-pressure noble gas ion chambers were adopted for measuring XAFS in transmission mode. In total electron yield (TEY) mode the current of sample is recorded. Solid, wet and liquid samples were suitable for this experimental station. Some representative results obtained from this station were shown and discussed.

Pressure-induced valence change of YbNiGe3investigated by resonant x-ray emission spectroscopy at the YbL3edge

Pressure dependence of the Yb valence in YbNiGe${}_{3}$ has been investigated up to 15.6 GPa at 300 K and up to 7.7 GPa at 17 K by means of x-ray absorption spectroscopy in $L{\ensuremath{\alpha}}_{1}$ partial fluorescence yield mode and resonant x-ray emission spectroscopy around the Yb ${L}_{3}$ absorption edge. The Yb valence in YbNiGe${}_{3}$ at ambient pressure strongly fluctuates with the mean valence of $v=2.52\ifmmode\pm\else\textpm\fi{}0.01$ at 300 K. The Yb valence rapidly changes toward a trivalent state with pressure up to $\ensuremath{\sim}$5 GPa, slowly increases up to $\ensuremath{\sim}$10 GPa, and then reaches a saturated value of $v\ensuremath{\sim}2.87$ at 15.6 GPa. The Yb valence at 17 K slightly decreases compared to that at 300 K; $v\ensuremath{\sim}2.45$ at ambient pressure and $\ensuremath{\sim}$$2.72$ at 7.7 GPa. We found that the pressure-induced change in the intensity of a quadrupole component in the x-ray absorption spectra shows the same trend as the Yb valence in YbNiGe${}_{3}$. In contrast to YbNiGe${}_{3}$, the Yb valence in YbNiSi${}_{3}$ is nearly 3 at ambient pressure with almost no temperature dependence.

Construction of a Wide-range High-resolution Beamline BL05 in NewSUBARU for Soft X-ray Spectroscopic Analysis on Industrial Materials

A material analysis beamline which is designed to useable in the wide energy range, 50~4000 eV for the various industrial demands, was constructed at BL05 in NewSUBARU for industrial companies' use in cooperation with the Laboratory of Advanced Science and Technology for Industry (LASTI), University of Hyogo and well-informed researchers in the industrial world. BL05 consists of two branch lines, which is mounted with a double crystal monochromator at BL05A and grating monochromator at BL05B. XAFS measurements in the total electron yield mode and partial fluorescence yield mode using a silicon drift detector can be performed at the both branch lines. In addition, the photoelectron spectra can be measured at BL05B. The maintenance and management of BL05 are performed by Synchrotron Analysis LLC (SALLC), which is a consortium of user companies of BL05, under the supervision of the LASTI staff. If industrial users want help with measurements at BL05, operators of SALLC can assist them.

ChemInform Abstract: Pressure‐Induced Valence and Structural Changes in YbMn2Ge2—Inelastic X‐Ray Spectroscopy and Theoretical Investigations.

AbstractPressure induced changes in the electronic structure of the title compound are investigated using high pressure XRD, resonant X‐ray emission spectroscopy, and X‐ray absorption spectroscopy in the partial fluorescence yield mode for pressures from ambient to 40 GPa.

Pressure-Induced Valence and Structural Changes in YbMn2Ge2—Inelastic X-ray Spectroscopy and Theoretical Investigations

The pressure-induced valence change of Yb in YbMn(2)Ge(2) has been studied by high pressure inelastic X-ray emission and absorption spectroscopy in the partial fluorescence yield mode up to 30 GPa. The crystal structure of YbMn(2)Ge(2) has been investigated by high pressure powder X-ray diffraction experiments up to 40 GPa. The experimental investigations have been complemented by first principles density functional theoretical calculations using the generalized gradient approximation with an evolutionary algorithm for structural determination. The Yb valence and magnetic structures have been calculated using the self-interaction corrected local spin density approximation. The X-ray emission results indicate a sharp increase of Yb valence from v = 2.42(2) to v = 2.75(3) around 1.35 GPa, and Yb reaches a near trivalent state (v = 2.95(3)) around 30 GPa. Further, a new monoclinic P1 type high pressure phase is found above 35 GPa; this structure is characterized by the Mn layer of the ambient (I4/mmm) structure transforming into a double layer. The theoretical calculations yield an effective valence of v = 2.48 at ambient pressure in agreement with experiment, although the pure trivalent state is attained theoretically at significantly higher pressures (above 40 GPa).

Electronic structure of Kondo lattice compounds YbNi3X9(X=Al, Ga) studied by hard x-ray spectroscopy

valences of YbNi3Ga9 and YbNi3Al9 at 22 K were evaluated to be 2.43 and 2.97, respectively. Based on the results of the Ni 2p and valence-band HAXPES spectra together with soft x-ray valence-band spectra, we described that the difference of physical properties of YbNi3X9 (X = Al, Ga) is derived from the differences of the 4f -hole level relative to the Fermi level (EF )a nd Ni 3d density of states at EF. The HAXPES results on the Yb valences were consistent with those obtained by x-ray absorption spectroscopy using the partial fluorescence yield mode and resonant x-ray emission spectroscopy at the Yb L3 edge.

Atomic and itinerant effects at the transition-metal x-ray absorptionKpre-edge exemplified in the case of V2O3

X-ray absorption spectroscopy is a well-established tool for obtaining information about orbital and spin degrees of freedom in transition-metal and rare-earth compounds. For this purpose usually the dipole transitions of the $L$ ($2p$ to $3d$) and $M$ ($3d$ to $4f$) edges are employed, whereas higher order transitions such as quadrupolar $1s$ to $3d$ in the $K$ edge are rarely studied in that respect. This is due to the fact that usually such quadrupolar transitions are overshadowed by dipole-allowed $1s$ to $4p$ transitions and, hence, are visible only as minor features in the pre-edge region. Nonetheless, these features carry a lot of valuable information, similar to the dipole $L$-edge transition, which is not accessible in experiments under pressure due to the absorption of the diamond anvil pressure cell. We recently performed a theoretical and experimental analysis of such a situation for the metal-insulator transition of (V${}_{(1\ensuremath{-}x)}$Cr${}_{x}$)${}_{2}$O${}_{3}$. Since the importance of the orbital degrees of freedom in this transition is widely accepted, a thorough understanding of quadrupole transitions of the vanadium $K$ pre-edge provides crucial information about the underlying physics. Moreover, the lack of inversion symmetry at the vanadium site leads to on-site mixing of vanadium $3d$ and $4p$ states and related quantum mechanical interferences between dipole and quadrupole transitions. Here we present a theoretical analysis of experimental high-resolution x-ray absorption spectroscopy at the V $K$ pre-edge measured in partial fluorescence yield mode for single crystals. We carried out density functional as well as configuration interaction calculations in order to capture effects coming from both itinerant and atomic limits.

X-ray-induced electronic structure change in CuIr2S4

The electronic structure of CuIr$_2$S$_4$ has been investigated using various bulk-sensitive x-ray spectroscopic methods near the Ir $L_3$-edge: resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy in the partial fluorescence yield (PFY-XAS) mode, and resonant x-ray emission spectroscopy (RXES). A strong RIXS signal (0.75 eV) resulting from a charge-density-wave gap opening is observed below the metal-insulator transition temperature of 230 K. The resultant modification of electronic structure is consistent with the density functional theory prediction. In the spin- and charge- dimer disordered phase induced by x-ray irradiation below 50 K, we find that a broad peak around 0.4 eV appears in the RIXS spectrum.

Resonant Inelastic X-ray Scattering at Ba-L3 Edge in BaTiO3

Resonant inelastic X-ray scattering (RIXS) measurements have been carried out at the Ba-L3 absorption edge on ferroelectric BaTiO3 for the first time. The absorption spectrum was measured in the partial fluorescence yield mode, by monitoring the intensity of the maximum of the Ba-Lα1 line through the Ba-L3 edge. The main peak, which reflects the unoccupied density of Ba 5d states, is found to be narrow, although broad shoulderlike tails appear towards both low and high energies. Using band structure calculations, these tails are ascribed to the strong hybridization between unoccupied Ba 5d and O 2p bands. Hybridization notwithstanding, the Ba 5d band is shown to retain a localized character, on the basis of the incident energy dependence of the Ba-Lα1 RIXS spectra.

Pressure-Induced Valence Crossover in SuperconductingCeCu2Si2

Measurement of the Ce valence in the heavy fermion CeCu(2)Si(2) is reported for the first time under pressure and at low temperature (T=14 K) in proximity of the superconducting region. CeCu(2)Si(2) is considered as a strong candidate for a new type of pairing mechanism related to critical valence fluctuations which could set in at high pressure in the vicinity of the second superconducting dome. A quantitative estimate of the valence in this pressure region was achieved from the measurements of the Ce L(3) edge in the high-resolution partial-fluorescence yield mode and subsequent analysis of the spectra within the Anderson impurity model. While a clear increase of the Ce valence is found, the weak electron transfer and the continuous valence change under pressure suggests a crossover regime with the hypothetical valence line terminating at a critical end point T(cr) close to zero.

Temperature and pressure-induced valence transitions inYbNi2Ge2andYbPd2Si2

We have measured the temperature and pressure-induced Yb valence transitions in tetragonal ${\text{YbNi}}_{2}{\text{Ge}}_{2}$ and ${\text{YbPd}}_{2}{\text{Si}}_{2}$ using x-ray absorption spectroscopy in the partial fluorescence yield mode and resonant x-ray emission spectroscopy. A temperature dependence of the Yb valence on the order of 0.1 has been measured, consistent with the magnetic-susceptibility study. The crossover from the low-temperature state having a stronger mixed valence to a high-temperature local moment behavior is analyzed within the Anderson impurity model. Pressure-induced second-order valence transitions are observed for both compounds with a more gradual transition in ${\text{YbPd}}_{2}{\text{Si}}_{2}$ than that of ${\text{YbNi}}_{2}{\text{Ge}}_{2}$. The mean valences are slightly less than $3+$ at ambient pressure but increase with applying pressure. Small variations in the Yb valence on the order of 0.03--0.05 can result in drastic change in the physical properties such as magnetic order and transport properties. Our results show that the Yb valence is noninteger around the quantum critical point.

Electronic structure of(Ce1−xNdx)3Alprobed by resonant x-ray emission spectroscopy

Bulk-sensitive measurements of the electronic structure of Ce in the ${({\text{Ce}}_{1\ensuremath{-}x}{\text{Nd}}_{x})}_{3}\text{Al}$ system have been performed as a function of temperature and $x$ using x-ray absorption spectroscopy in the partial fluorescence yield mode and resonant x-ray emission spectroscopy (RXES) at the $\text{Ce}\text{ }{L}_{3}$ edge. In the Ce-rich samples, the RXES spectra indicate a mixed-valence state consisting mainly of ${f}^{1}$ with a small fraction of ${f}^{0}$ and ${f}^{2}$. The ${f}^{1}/{f}^{2}$ intensity ratio is found to undergo a first-order transition at low temperature, coinciding with the $\ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\gamma}$ structural transition. Following the disappearance of the Kondo effect at $x>0.2$, the ${f}^{1}/{f}^{2}$ intensity ratio is found to significantly increase with $x$, signifying a weakening of the mixed-valence character. The fact that the volume remains nearly constant upon Nd doping points to an electronic origin of the $x$ dependence of the $\text{Ce}\text{ }{f}^{1}/{f}^{2}$ intensity ratio.

Pressure-induced valence change inYbAl3: A combined high-pressure inelastic x-ray scattering and theoretical investigation

High-resolution x-ray-absorption XAS experiments in the partial fluorescence yield mode PFY and resonant inelastic x-ray emission RXES measurements were performed on the intermediate-valence compound YbAl3 under pressure of up to 38 GPa. The results of the YbAl3 PFY-XAS and RXES studies show that the valence of Yb increases smoothly from 2.75 at ambient pressure to 2.93 at 38 GPa. In situ angle-dispersive synchrotron high-pressure x-ray-diffraction experiments carried out using a diamond cell at room temperature show that the ambient pressure cubic phase is stable up to 40 GPa. The results obtained from self-interaction corrected local spin density-functional calculations to understand the pressure effect on the Yb valence and compressibility are in good agreement with the experimental results.

The semiconductor to metal transition in [formula omitted] probed by high resolution X-ray absorption spectroscopy

The substituted system FeSi 1 - x Ge x undergoes a semiconductor to metal transition at x ∼ 0.25 . We investigated the electronic structure for the x = 0 , 0.19 and 0.44 compounds using X-ray absorption spectroscopy in the partial fluorescence yield mode (PFY-XAS) at the Fe K-edge. The position of the edge showed no x or temperature dependence, and agreed with that of metal Fe. These results are consistent with the band calculations.