Valence-contrast studies by resonant diffraction with synchrotron radiation; the rôle of X-ray absorption measurements

1992 ◽  
Vol 25 (5) ◽  
pp. 654-657 ◽  
Author(s):  
A. P. Wilkinson ◽  
A. K. Cheetham
Keyword(s):  
Optical Theorem ◽  
Anomalous Scattering ◽  
X Rays ◽  
Acta Cryst ◽  
X Ray ◽  
X Ray Absorption ◽  
Kronig Relation ◽  
Absorption Measurements ◽  
Good Agreement

The X-ray absorption spectra of GaCl2, GaAlCl4 and GaCl3 have been measured in the vicinity of the Ga K edge and values of f′′ and f′ estimated for GaI and GaIII from the latter two spectra by using the optical theorem and the Kramers–Kronig relation. The resulting f′ values are compared with those previously determined from anomalous-scattering measurements with synchrotron X-rays on the compound GaCl2 [Wilkinson, Cheetham & Cox (1991). Acta Cryst. B47, 155–161] and found to be in good agreement. The use of anomalous scattering methods for distinguishing oxidation states is discussed in the light of these results and others found in the literature.

Superstructure Determination of PbZrO3

1998 ◽  
Vol 54 (5) ◽  
pp. 524-530 ◽  
Author(s):  
K. Yamasaki ◽  
Y. Soejima ◽  
K. F. Fischer
Keyword(s):  
Structure Refinement ◽  
Lead Zirconate ◽  
X Rays ◽  
Linear Absorption Coefficient ◽  
Linear Absorption ◽  
Acta Cryst ◽  
X Ray ◽  
Domain Structures ◽  
X Ray Absorption

By taking into account the effects of domain structures and X-ray absorption, the superstructure of PbZrO3, lead zirconate, has been determined at room temperature. The space group is Pbam with a unit cell of a = 5.8884 (19), b = 11.771 (4) and c = 8.226 (3) Å, with Z = 8. The intensity data were collected using short-wavelength synchrotron X-rays of 0.350 Å; this reduces the linear absorption coefficient to 11.93 mm−1. The structure refinement was performed using only the data of superlattice reflections which are free from ambiguity and resulting from the domain structure; the final R value is 0.047 for 335 unique superlattice reflections. Zr atoms show the antiphase-type displacement along the z axis; oxygen octahedra show tilt of the type a − a − c 0 using Glazer's [Acta Cryst. (1972), B28, 3384–3392; Acta Cryst. (1975), A31, 756–762] notation.

scholarly journals Experimentally obtained and computer-simulated X-ray asymmetric eight-beam pinhole topographs for a silicon crystal

2019 ◽  
Vol 75 (3) ◽  
pp. 474-482 ◽  
Author(s):  
Kouhei Okitsu ◽  
Yasuhiko Imai ◽  
Yoshitaka Yoda ◽  
Yoshinori Ueji
Keyword(s):  
Eigenvalue Problem ◽  
Fourier Transformation ◽  
Silicon Crystal ◽  
Fast Fourier Transformation ◽  
X Rays ◽  
Acta Cryst ◽  
X Ray ◽  
Simulated Images ◽  
Laue Geometry ◽  
Good Agreement

In this study, experimentally obtained eight-beam pinhole topographs for a silicon crystal using synchrotron X-rays were compared with computer-simulated images, and were found to be in good agreement. The experiment was performed with an asymmetric all-Laue geometry. However, the X-rays exited from both the bottom and side surfaces of the crystal. The simulations were performed using two different approaches: one was the integration of the n-beam Takagi–Taupin equation, and the second was the fast Fourier transformation of the X-ray amplitudes obtained by solving the eigenvalue problem of the n-beam Ewald–Laue theory as reported by Kohn & Khikhlukha [Acta Cryst. (2016), A72, 349–356] and Kohn [Acta Cryst. (2017), A73, 30–38].

scholarly journals The M82 Outflow: X-rays as a Probe for Neutral Disk Gas

2004 ◽  
Vol 217 ◽  
pp. 312-313
Author(s):  
Jürgen Ott ◽  
Fabian Walter ◽  
Jürgen Kerp
Keyword(s):  
Starburst Galaxy ◽  
Transition Line ◽  
X Rays ◽  
X Ray ◽  
X Ray Absorption ◽  
Good Agreement

We present an analysis of X-ray absorption in the nearby starburst galaxy M82. The X-ray attenuating column densities in the northern part of the M 82 outflow can be associated with cold disk gas detected in maps of H1 and CO (1→0). We derive an XCO factor which is somewhat lower as compared to that in our Galaxy. This is in good agreement with multi-transition line studies of various molecules in the disk of M 82.

scholarly journals Long-wavelength native-SAD phasing: opportunities and challenges

IUCrJ ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 373-386 ◽  
Author(s):  
Shibom Basu ◽  
Vincent Olieric ◽  
Filip Leonarski ◽  
Naohiro Matsugaki ◽  
Yoshiaki Kawano ◽  
...  
Keyword(s):  
Anomalous Scattering ◽  
X Rays ◽  
X Ray ◽  
Long Wavelength ◽  
Experimental Phasing ◽  
Sad Phasing ◽  
Anomalous Signal ◽  
Scattering Factor ◽  
X Ray Absorption

Native single-wavelength anomalous dispersion (SAD) is an attractive experimental phasing technique as it exploits weak anomalous signals from intrinsic light scatterers (Z < 20). The anomalous signal of sulfur in particular, is enhanced at long wavelengths, however the absorption of diffracted X-rays owing to the crystal, the sample support and air affects the recorded intensities. Thereby, the optimal measurable anomalous signals primarily depend on the counterplay of the absorption and the anomalous scattering factor at a given X-ray wavelength. Here, the benefit of using a wavelength of 2.7 over 1.9 Å is demonstrated for native-SAD phasing on a 266 kDa multiprotein-ligand tubulin complex (T2R-TTL) and is applied in the structure determination of an 86 kDa helicase Sen1 protein at beamline BL-1A of the KEK Photon Factory, Japan. Furthermore, X-ray absorption at long wavelengths was controlled by shaping a lysozyme crystal into spheres of defined thicknesses using a deep-UV laser, and a systematic comparison between wavelengths of 2.7 and 3.3 Å is reported for native SAD. The potential of laser-shaping technology and other challenges for an optimized native-SAD experiment at wavelengths >3 Å are discussed.

Determination of the Anomalous Scattering Factors in the Soft-X-ray Range using Diffraction from a Multilayer

1998 ◽  
Vol 31 (5) ◽  
pp. 700-707 ◽  
Author(s):  
L. Sève ◽  
J. M. Tonnerre ◽  
D. Raoux
Keyword(s):  
Fluorescence Yield ◽  
Bragg Diffraction ◽  
Anomalous Scattering ◽  
Total Electron Yield ◽  
Total Electron ◽  
X Ray ◽  
Scattering Factor ◽  
X Ray Absorption ◽  
Kronig Relation

Bragg diffraction from an Ag/Ni multilayer was used to determine independently both the real and imaginary parts of the anomalous scattering factor (ASF) around the NiLIIIandLIIedges in the soft-X-ray range. Huge resonant variations were observed with f'' reaching 55\,r_o and f' decreasing to −63 r_o at the NiLIIIedge. The independent measurements of f' and f'' are tested for coherency using the Kramers–Kronig relation. The f'' values are also compared with those derived from X-ray absorption methods such as total electron yield and fluorescence yield measurements.

Determination of the anomalous scattering factors for Cu, Ni and Ti using the dispersion relation

1984 ◽  
Vol 17 (5) ◽  
pp. 344-351 ◽  
Author(s):  
J. J. Hoyt ◽  
D. de Fontaine ◽  
W. K. Warburton
Keyword(s):  
Dispersion Relation ◽  
Optical Theorem ◽  
Anomalous Scattering ◽  
X Ray ◽  
Atomic Scattering ◽  
Experimental Errors ◽  
Scattering Factor ◽  
Radiation Laboratory ◽  
X Ray Absorption

X-ray absorption spectra about the K edges of Ni, Cu and Ti have been measured at the Stanford Synchrotron Radiation Laboratory. The imaginary part of the atomic scattering factor f′′ was determined using the optical theorem and the real part f′ computed by the Kramers–Kronig dispersion relation. Methods for evaluating this integral as well as the effects on f′ of various experimental errors are investigated. The f′ results for Cu and Ni are compared to data from interferometry experiments.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

X-Ray absorption edge elemental imaging of B. thuringienis

1989 ◽  
Vol 47 ◽  
pp. 212-213
Author(s):  
R. L. Stears
Keyword(s):  
Absorption Edge ◽  
Elemental Distribution ◽  
X Rays ◽  
Differential Absorption ◽  
Synchrotron Source ◽  
High Brightness ◽  
X Ray ◽  
Elemental Imaging ◽  
Cellular Integrity ◽  
X Ray Absorption

Because of the nature of the bacterial endospore, little work has been done on analyzing their elemental distribution and composition in the intact, living, hydrated state. The majority of the qualitative analysis entailed intensive disruption and processing of the endospores, which effects their cellular integrity and composition.Absorption edge imaging permits elemental analysis of hydrated, unstained specimens at high resolution. By taking advantage of differential absorption of x-ray photons in regions of varying elemental composition, and using a high brightness, tuneable synchrotron source to obtain monochromatic x-rays, contact x-ray micrographs can be made of unfixed, intact endospores that reveal sites of elemental localization. This study presents new data demonstrating the application of x-ray absorption edge imaging to produce elemental information about nitrogen (N) and calcium (Ca) localization using Bacillus thuringiensis as the test specimen.

scholarly journals Al-driven peculiarities of local coordination and magnetic properties in single-phase Alx-CrFeCoNi high-entropy alloys

Nano Research ◽  
2021 ◽  
Author(s):  
Alevtina Smekhova ◽  
Alexei Kuzmin ◽  
Konrad Siemensmeyer ◽  
Chen Luo ◽  
Kai Chen ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Single Phase ◽  
Magnetic Circular Dichroism ◽  
Surface Region ◽  
Face Centered Cubic ◽  
X Rays ◽  
X Ray ◽  
High Entropy ◽  
X Ray Absorption ◽  
Absorption Edges

AbstractModern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties. Herein, peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic (fcc)- and body-centered cubic (bcc)-structured high-entropy Alx-CrFeCoNi alloys (x = 0.3 and 3, respectively) are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges. Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision. The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry. A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account. X-ray magnetic circular dichroism technique employed at L2.3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values. Extended to nanostructured versions of multicomponent alloys, such studies would bring new insights related to effects of high entropy mixing on low dimensions.

scholarly journals Synchrotron X-ray induced acoustic imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Seongwook Choi ◽  
Eun-Yeong Park ◽  
Sinyoung Park ◽  
Jong Hyun Kim ◽  
Chulhong Kim
Keyword(s):  
Acoustic Imaging ◽  
Signal Frequency ◽  
X Rays ◽  
Repetition Period ◽  
Linear Accelerators ◽  
X Ray ◽  
X Ray Computed ◽  
Medical Linear Accelerators ◽  
Ionizing Radiation Exposure ◽  
X Ray Absorption

AbstractX-ray induced acoustic imaging (XAI) is an emerging biomedical imaging technique that can visualize X-ray absorption contrast at ultrasound resolution with less ionizing radiation exposure than conventional X-ray computed tomography. So far, medical linear accelerators or industrial portable X-ray tubes have been explored as X-ray excitation sources for XAI. Here, we demonstrate the first feasible synchrotron XAI (sXAI). The synchrotron generates X-rays, with a dominant energy of 4 to 30 keV, a pulse-width of 30 ps, a pulse-repetition period of 2 ns, and a bunch-repetition period of 940 ns. The X-ray induced acoustic (XA) signals are processed in the Fourier domain by matching the signal frequency with the bunch-repetition frequency. We successfully obtained two-dimensional XA images of various lead targets. This novel sXAI tool could complement conventional synchrotron applications.

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