X-ray Fluorescence Holography Research Articles

Local Structure Analysis on Yttria-Stabilized Zirconia by X-ray Fluorescence Holography

Local Structure Analysis on Yttria-Stabilized Zirconia by X-ray Fluorescence Holography

Significant displacement of calcium and barium ions in ferroelectric (Ba0.9Ca0.1)TiO3 revealed by x-ray fluorescence holography

The x-ray fluorescence holography technique is applied to perovskite (Ba0.9Ca0.1)TiO3 ferroelectrics in order to investigate the local structures around the Ca and Ba ions at the A-site. While the A-site atomic images around the Ba ion can be well understood based on the BaTiO3 structure, those around the Ca ion are located at the closer positions to the emitter. Furthermore, the shape of the atomic image around the Ca ion is elongated in the radial direction. These features clearly show the local lattice contraction around the Ca ion and a significant displacement of the Ca ions from the ideal position. On the basis of the detailed analysis of the position and the shape of the atomic image around the Ca ion, it is found that the Ca ions are displaced by ∼0.36 Å in the ⟨111⟩ direction, and the surrounding Ba ions are displaced by ∼0.22 Å in the ⟨100⟩ direction. The present results indicate that the doped Ca ions activate the A-site polarization of this compound, which can lead to an enhancement of the ferroelectric and piezoelectric performances.

Three-dimensional Atomic Image of FeSe High-temperature Superconductor by X-ray Fluorescence Holography

Fe Kα X-ray fluorescence holography measurements were carried out at room temperature on an FeSe high-temperature superconductor to clarify the relationship between the local structures around the Fe atoms and the superconducting nature. The obtained three-dimensional atomic arrangements strongly reveal a formation of strong FeSe4 clusters. On the other hand, the Se—Fe—Se bond angle largely spreads, causing a large ambiguity in the chalcogen height and large displacements of the Fe sublattice. Thus, it is reasonable that the tetragonal-to-orthorhombic structural (nematic) transition does not affect the magnetic ordering in the Fe layer.

X-ray Fluorescence Holography Measurement of Oxynitride Thin Film of CaTaO<sub>2</sub>N

X-ray Fluorescence Holography Measurement of Oxynitride Thin Film of CaTaO<sub>2</sub>N

Element-selective local structural analysis around B -site cations in multiferroic Pb(Fe1/2Nb1/2)O3 using x-ray fluorescence holography

X-ray fluorescence holography (XFH) measurements were carried out for multiferroic $\mathrm{Pb}({\mathrm{Fe}}_{1/2}{\mathrm{Nb}}_{1/2}){\mathrm{O}}_{3}$ (PFN) single crystal to investigate variations in the local structures around Nb ions with decreasing temperature from 300 to 100 K, in combination with single-crystal x-ray diffraction (XRD) experiments. We find that the Nb--Pb correlation is more significantly changed by cooling than the average structure derived from the single-crystal XRD experiments, indicating a mobile feature of Nb ions. Also, we analyze previously obtained XFH results around Fe ions in detail for comparison with those around Nb ions. In contrast to the case of Nb ions, the variation in the Fe--Pb correlation with decreasing temperature is well explained by the average structure from 300 K down to the N\'eel temperature of about 150 K. On the other hand, a remarkable positional fluctuation between Fe and Pb ions is observed at 100 K, which is evaluated to be 90% larger than that between Nb and Pb ions. This observation strongly indicates the presence of spin-lattice coupling in PFN. The present study clearly elucidates the differences of local environment around the Nb ions from that around the Fe ions located at the same $B$-site.

A cryostat designed for x-ray fluorescence holography experiments down to 4 K.

A cryostat was designed for x-ray fluorescence holography (XFH) experiments at low temperatures down to 4K, where many functional materials show characteristic transitions, such as high-temperature superconducting, magnetic, dielectric, and valence transitions. For XFH measurements, changes in two angles of samples with respect to the incident synchrotron x-ray beam, i.e., incident angle θ and azimuthal angle ϕ, are necessary. A low-temperature specialized small piezoelectric motor is installed at the cryostat head for ϕ, and the cryostat itself is rotated by a stepping motor for θ. The heat from the piezoelectric motor for ϕ and the cryostat power determining the total cryostat mass were optimized for the limited working spaces and beamtimes of synchrotron experiments. Some examples of the XFH results at low temperatures, such as a Pb crystal and an YbInCu4 valence transition material, are presented to show the feasibility of this low-temperature equipment.

Elucidation of local structure deformation in κ−(BEDT−TTF)2Cu[N(CN)2]Br by x-ray fluorescence holography

$\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Br} (\ensuremath{\kappa}\text{\ensuremath{-}}\mathrm{Br})$ is an organic superconductor that changes to an Anderson-type insulator due to the random defects introduced by x-ray irradiation. In this study, we directly investigated the effects of irradiation on the local structures in the anion layer of $\ensuremath{\kappa}\text{\ensuremath{-}}\mathrm{Br}$ using x-ray fluorescence holography. The local structures around the Cu atoms in the anion layer were directly reconstructed from holograms. Prior to radiation damage, the reconstruction clearly shows the atomic images of the Br and N atoms that are directly coordinated to Cu. In the irradiated samples, the N images in the reconstructions were strongly suppressed as a result of the positional fluctuations of N introduced by the defects induced by irradiation. Using the previously proposed ``bond-shifted'' model and the thermal vibration amplitudes calculated from molecular dynamics simulations, we simulated the holograms and the atomic reconstructions of the anion layer. The simulations show that the ``bond-shifted'' model, along with thermal vibrations at 100 K, suppresses the N atomic images, as was observed in the experimental reconstructions.

The Local Structure of the Fibonacci Chain and the Penrose Tiling from X-Ray Fluorescence Holography

The Local Structure of the Fibonacci Chain and the Penrose Tiling from X-Ray Fluorescence Holography

Average and Local Crystal Structures of Multiferroic Eu1−xYxMnO3 (x = 0.2 and 0.4)

Crystal structures of the multiferroic Eu1−xYxMnO3 (x = 0.2, 0.4) are investigated from the point of view of average and local structure analyses using single‐crystal X‐ray diffraction (XRD) and X‐ray fluorescence holography (XFH). With increasing Y content, the lattice constants decrease and the orthorhombic distortions increase. The differences between the local structures around Eu and Y are observed in the reconstructed atomic images by XFH. x = 0.2 and 0.4 compounds exhibit different local distortions at Mn sites, whereas no characteristic difference is shown in the average structures. In this system, the long‐range structural coherence is likely to be maintained even with significant substitution of Y.

Reconstruction of evolving nanostructures in ultrathin films with X-ray waveguide fluorescence holography

Controlled synthesis of nanostructure ultrathin films is critical for applications in nanoelectronics, photonics, and energy generation and storage. The paucity of structural probes that are sensitive to nanometer-thick films and also capable of in-operando conditions with high spatiotemporal resolutions limits the understanding of morphology and dynamics in ultrathin films. Similar to X-ray fluorescence holography for crystals, where holograms are formed through the interference between the reference and the object waves, we demonstrated that an ultrathin film, being an X-ray waveguide, can also generate fluorescence holograms as a result of the establishment of X-ray standing waves. Coupled with model-independent reconstruction algorithms based on rigorous dynamical scattering theories, the thin-film-based X-ray waveguide fluorescence holography becomes a unique in situ and time-resolved imaging probe capable of elucidating the real-time nanostructure kinetics with unprecedented resolutions. Combined with chemical sensitive spectroscopic analysis, the reconstruction can yield element-specific morphology of embedding nanostructures in ultrathin films.

Valence-Selective Local Atomic Structures on an YbInCu4 Valence Transition Material by X-Ray Fluorescence Holography

An experimental technique of x-ray fluorescence holography for investigating valence-selective local structures was established by employing a characteristic incident x-ray energy near an absorptio...

Local structure and atomic dynamics in Fe2VAl Heusler-type thermoelectric material: The effect of heavy element doping

X-ray absorption fine structure (XAFS), x-ray fluorescence holography (XFH), and inelastic x-ray scattering (IXS) techniques were applied to an ${\mathrm{Fe}}_{2}({\mathrm{V}}_{0.95}{\mathrm{Ta}}_{0.05}$)Al Heusler-type thermoelectric material to investigate the doping effect of Ta on the local structure and the atomic dynamics. The XAFS and XFH results show that the positional correlation between Ta and surrounding Fe atoms is much more rigid than that between V and Fe. In the IXS results, we observed a broad dispersionless mode in the energy range of the acoustic phonons of undoped ${\mathrm{Fe}}_{2}\mathrm{VAl}$, which is regarded as the so-called resonant mode. These results revealed a clearly different feature of the dynamics of heavy dopants from that of the matrix element, which disturbs the coherency of phonons and should contribute to the enhancement of the thermal insulation.

Nanoscopic X-ray imaging and quantification of the iron cellular architecture within single fibroblasts of Friedreich's ataxia patients.

Friedreich's ataxia (FRDA) is a neurodegenerative disease characterized by an increase in intracytoplasmic iron concentration. Here the nanoscale iron distribution within single fibroblasts from FRDA patients was investigated using synchrotron-radiation-based nanoscopic X-ray fluorescence and X-ray in-line holography at the ID16A nano-imaging beamline of the ESRF. This unique probe was deployed to uncover the iron cellular two-dimensional architecture of freeze-dried FRDA fibroblasts. An unsurpassed absolute detection capability of 180 iron atoms within a 30 nm × 50 nm nanoscopic X-ray beam footprint was obtained using state-of-the-art X-ray focusing optics and a large-solid-angle detection system. Various micrometre-sized iron-rich organelles could be revealed for the first time, tentatively identified as endoplasmic reticulum, mitochondria and lysosomes. Also a multitude of nanoscopic iron hot-spots were observed in the cytosol, interpreted as chaperoned iron within the fibroblast's labile iron pool. These observations enable new hypotheses on the storage and trafficking of iron in the cell and ultimately to a better understanding of iron-storage diseases such as Friedreich's ataxia.

Analyses on atomic arrangement in dielectric ε-Ga2O3 epitaxial thin films

Local atomic arrangements of dielectric ε-Ga2O3 epitaxial thin films grown on indium doped tin oxide (ITO) and α-Al2O3 substrates were investigated by combining transmission electron microscopy (TEM) and X-ray fluorescence holography (XFH). TEM showed the orthorhombic lattice structure for the ε-Ga2O3 thin film on both the substrates and a significant in-plane Ga ion displacement on α-Al2O3. However, XFH revealed a partial disorder of Ga vacancies and a large displacement along the a-axis on ITO. On the other hand, highly ordered Ga vacancies and a displacement of Ga ions toward the Ga vacancy sites were observed for the film on α-Al2O3 by XFH. Such a high degree of freedom in atomic sites and displacements is believed to contribute to a high dielectric constant of ε-Ga2O3.

Atomic structure stabilization in BiFeO3 thin film by Mn doping

This study experimentally investigated the atomic structure of a single-crystalline Mn-doped BiFeO3 (BFO) thin film using X-ray fluorescence holography with synchrotron radiation. Bi atoms can be reconstructed from both Fe Kβ and Mn Kα fluorescence X-ray holograms, indicating Mn doping at B sites in ABO3-type perovskite structure. The fluorescence intensity of the 1st to 4th nearest Bi atoms around target Fe atoms was lower than those around Mn atoms, confirming the selective formation of Bi vacancies around Fe atoms. In contrast, the 5th to 8th nearest Bi atoms around Fe atoms showed higher intensities than those around Mn atoms, indicating that the Mn-doped BFO thin film had a double-perovskite-like structure. These results provide important information that helps elucidate the mechanism by which Mn doping modifies the conductivity of BFO.

Local environment of W and Mo atoms in CaW1−xMoxO4 (x = 0.12) solid solution studied by X-ray structural analyzes

The local environment of W and Mo atoms in CaW1−xMoxO4 (x = 0.12) solid solution (mixed crystal) scintillator crystal was analyzed by X-ray diffraction (XD), extended X-ray absorption fine structure (EXAFS), and X-ray fluorescence holography (XFH). The XD analysis revealed that W and Mo atoms occupy the same crystallographic site. The analyzes of XFH and EXAFS exhibited that the local environment of Mo atoms is different from that of W atoms. Atomic images of neighbor atoms around the Mo and W atoms were reconstructed using their positional fluctuations. The positional fluctuation of the W atoms was apparently larger than that of Mo atoms. This feature explained the absence of the peak due to next nearest neighbor O atoms around W atoms in the Fourier transfer magnitudes for the W-L3 edge EXAFS spectrum. It is, therefore, most likely that the different positional fluctuations of the Mo and W atoms are responsible for different atomic images of neighbor atoms between them.

Valence-selective local atomic structures in inorganic materials by X-ray fluorescence holography

X-ray fluorescence holography (XFH) can be used to conduct atom-resolved structural characterization of materials around a specific element, and has been applied to various functional materials. Recently, a valence-selective function has been found by this technique by employing incident X-ray energies near an absorption edge of a specified element. In this article, the principle and experimental procedure of a valence-selective XFH and subsequent data analysis procedure using the sparse modeling approach of L1 regression are introduced. Then, the excellent XFH results with valence-selective studies are reviewed, such as Y oxide thin film, YbInCu4 valence transition material, and Fe3O4 mixed valence material.

Local structural analysis of Pb(Fe1/2Nb1/2)O3 multiferroic material using X-ray fluorescence holography

We performed X-ray fluorescence holography measurements on a Pb(Fe1/2Nb1/2)O3 (PFN) multiferroic material in order to investigate the temperature dependence of three dimensional local structure around Fe atoms. It was found that the atomic image intensity of the nearest neighbor Pb atom abruptly decreases when the temperature becomes lower than the Néel temperature (TN) of about 150 K, while the intensity of the atomic image at nearest Fe/Nb position remains almost unchanged. These observations show that the magnetic transition at TN induces static positional shifts of Pb atoms but does not strongly influence the Fe/Nb atoms, which suggests the involvement of Pb ions into the superexchange interaction between Fe ions and its contribution to the spin-lattice coupling in PFN.

Three-dimensional local atomic configurations of decagonal AlNiCo quasicrystal studied by X-ray fluorescence holography

Three-dimensional local atomic configurations of decagonal AlNiCo quasicrystal studied by X-ray fluorescence holography

Impact of Local Atomic Fluctuations on Superconductivity of Pr-Substituted CaFe2As2 Studied by X-ray Fluorescence Holography

The local structures of Ca1−xPrxFe2As2 (\(x = 0,0.1\)) were studied by X-ray fluorescence holography. Significant fluctuations were observed in As positions for CaFe2As2. The fluctuations increased...