High accuracy determination of photoelectric cross sections, X-ray absorption fine structure and nanostructure analysis of zinc selenide using the X-ray extended range technique

2020 ◽  
Vol 27 (5) ◽  
pp. 1262-1277
Author(s):  
Daniel Sier ◽  
Geoffrey P. Cousland ◽  
Ryan M. Trevorah ◽  
Ruwini S. K. Ekanayake ◽  
Chanh Q. Tran ◽  
...  

Measurements of mass attenuation coefficients and X-ray absorption fine structure (XAFS) of zinc selenide (ZnSe) are reported to accuracies typically better than 0.13%. The high accuracy of the results presented here is due to our successful implementation of the X-ray extended range technique, a relatively new methodology, which can be set up on most synchrotron X-ray beamlines. 561 attenuation coefficients were recorded in the energy range 6.8–15 keV with measurements concentrated at the zinc and selenium pre-edge, near-edge and fine-structure absorption edge regions. This accuracy yielded detailed nanostructural analysis of room-temperature ZnSe with full uncertainty propagation. Bond lengths, accurate to 0.003 Å to 0.009 Å, or 0.1% to 0.3%, are plausible and physical. Small variation from a crystalline structure suggests local dynamic motion beyond that of a standard crystal lattice, noting that XAFS is sensitive to dynamic correlated motion. The results obtained in this work are the most accurate to date with comparisons with theoretically determined values of the attenuation showing discrepancies from literature theory of up to 4%, motivating further investigation into the origin of such discrepancies.

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Ruwini S. K. Ekanayake ◽  
Christopher T. Chantler ◽  
Daniel Sier ◽  
Martin J. Schalken ◽  
Alexis J. Illig ◽  
...  

The first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron, Australia, is presented. In this experiment X-ray mass attenuation coefficients are measured across an energy range including the zinc K-absorption edge and X-ray absorption fine structure (XAFS). These high-accuracy measurements are recorded at 496 energies from 8.51 keV to 11.59 keV. The XERT protocol dictates that systematic errors due to dark current nonlinearities, correction for blank measurements, full-foil mapping to characterize the absolute value of attenuation, scattering, harmonics and roughness are measured over an extended range of experimental parameter space. This results in data for better analysis, culminating in measurement of mass attenuation coefficients across the zinc K-edge to 0.023–0.036% accuracy. Dark current corrections are energy- and structure-dependent and the magnitude of correction reached 57% for thicker samples but was still large and significant for thin samples. Blank measurements scaled thin foil attenuation coefficients by 60–500%; and up to 90% even for thicker foils. Full-foil mapping and characterization corrected discrepancies between foils of up to 20%, rendering the possibility of absolute measurements of attenuation. Fluorescence scattering was also a major correction. Harmonics, roughness and bandwidth were explored. The energy was calibrated using standard reference foils. These results represent the most extensive and accurate measurements of zinc which enable investigations of discrepancies between current theory and experiments. This work was almost fully automated from this first experiment at the Australian Synchrotron, greatly increasing the possibility for large-scale studies using XERT.


2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Ruwini S. K. Ekanayake ◽  
Christopher T. Chantler ◽  
Daniel Sier ◽  
Martin J. Schalken ◽  
Alexis J. Illig ◽  
...  

High-accuracy X-ray mass attenuation coefficients were measured from the first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron. Experimentally measured mass attenuation coefficients deviate by ∼50% from the theoretical values near the zinc absorption edge, suggesting that improvements in theoretical tabulations of mass attenuation coefficients are required to bring them into better agreement with experiment. Using these values the imaginary component of the atomic form factor of zinc was determined for all the measured photon energies. The zinc K-edge jump ratio and jump factor are determined and results raise significant questions regarding the definitions of quantities used and best practice for background subtraction prior to X-ray absorption fine-structure (XAFS) analysis. The XAFS analysis shows excellent agreement between the measured and tabulated values and yields bond lengths and nanostructure of zinc with uncertainties of from 0.1% to 0.3% or 0.003 Å to 0.008 Å. Significant variation from the reported crystal structure was observed, suggesting local dynamic motion of the standard crystal lattice. XAFS is sensitive to dynamic correlated motion and in principle is capable of observing local dynamic motion beyond the reach of conventional crystallography. These results for the zinc absorption coefficient, XAFS and structure are the most accurate structural refinements of zinc at room temperature.


2014 ◽  
Vol 70 (a1) ◽  
pp. C960-C960 ◽  
Author(s):  
Lachlan Tantau ◽  
Christopher Chantler ◽  
Md Islam ◽  
Jay Bourke

We present recent experimental X-ray Absorption Fine Structure (XAFS) data of the Nickel K-edge, measured at temperatures of 15, 70 and 140 K. This study has taken elements of the X-ray Extended Range Technique (XERT) and for the first time, applied them to a cryostat cold cell system. These measurements permit critical tests of XAFS theory, with emphasis on quantification of the Debye-Waller factor and static vs. thermal disorder. X-ray Absorption Fine Structure contains vital information about the surrounding system of an absorbing atom including crystal structure, bond distances and coordination number. It is crucial that we understand all processes that may affect the measured XAFS spectra. The aim of this study is to investigate thermal effects and quantify thermal and static disorder [1]. The XERT is an experimental technique developed by our group, capable of measuring X-ray mass attenuation coefficients on an absolute scale with accuracies down to 0.02% [2]. This study has taken crucial elements from the XERT and applied them to complex experimental systems. This includes, but is not limited to high accuracy energy calibration [3], quantification and correction of beam harmonics and fluorescence. Our robust technique allows us to take the high accuracy data required to determine fundamental structural and crystallographic properties. These developments give great insight into our understanding of more complex systems such as organometallic molecules and biological systems.


2000 ◽  
Vol 454-456 ◽  
pp. 723-728 ◽  
Author(s):  
H. Magnan ◽  
P. Le Fèvre ◽  
A. Midoir ◽  
D. Chandesris ◽  
H. Jaffrès ◽  
...  

Author(s):  
Kazumasa Murata ◽  
Junya Ohyama ◽  
Atsushi Satsuma

In the present study, the redispersion behavior of Ag particles on ZSM-5 in the presence of coke was observed using in situ X-ray absorption fine structure (XAFS) spectroscopy.


2021 ◽  
Author(s):  
Gregory M. Su ◽  
Han Wang ◽  
Brandon R. Barnett ◽  
Jeffrey R. Long ◽  
David Prendergast ◽  
...  

In situ near edge X-ray absorption fine structure spectroscopy directly probes unoccupied states associated with backbonding interactions between the open metal site in a metal–organic framework and various small molecule guests.


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