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

Abstract

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.

High-accuracy measurement of mass attenuation coefficients and the imaginary component of the atomic form factor of zinc from 8.51 keV to 11.59 keV, and X-ray absorption fine structure with investigation of zinc theory and nanostructure

“…The widespread use of XRF and EDXRF argues strongly for increased understanding of these ratios and how to use and interpret them; the propagation errors and uncertainties of XANES and XAFS analysis, especially at low k, depend upon the stability and uniqueness of the definition of the edge and spline or other background subtraction; and more theoretical and experimental work is required in this area in attenuation, absorption and fluorescence measurements. Immediately, we can use this analysis to justify the data presented herein; and to emphasize or demonstrate the error of Singh Sidhu et al Previous work to obtain the edge jumps of the zinc K-edge using this method (Sier et al, 2020) on zinc selenide found the jump ratio to be r K, tot = 3.380. However, as this work was conducted on a compound, this value must be scaled by the relative atomic composition of zinc within zinc selenide (0.453) which converts the value to r K, tot = 7.461 as the attenuation ratio; and to r K = 3.406 as the photoabsorption ratio in the compound, and r K = 7.519 as the photoabsorption ratio for the Zn.…”

“…We, however, measure the zinc K-edge jump, jump ratio and jump factor from the current data herein and hence use an alternative XERT-like method. Synchrotron X-rays are allowed to pass through the sample to measure attenuation coefficients, from which photoabsorption coefficients and edge-jump ratios can be derived (Chantler et al, 2001;Rae et al, 2010;Sier et al, 2020). Following Fig.…”

High-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique

“…A = 1/[t] from the thickness determination, f is the fluorescence counts and , are constants to be fitted. and define the fraction of fluorescence which enters the upstream and downstream (fluorescence) detectors (Sier et al, 2020;Trevorah et al, 2019;Islam et al, 2015). Upon inspection, any scattering is below the noise level in the upstream ion chamber -hence is set to zero, with particularly fitted from the high-energy E or high k-range.…”

“…Hence it is particularly important if there are any energy-dependent functionalities above the edge. Previous work with zinc at the same beamline measured the scattering and fluorescence contributions in each ion chamber (Sier et al, 2020;Trevorah et al, 2019;Islam et al, 2015). Hence we require a functional to match the scattering correction of each data set.…”

“…A temperature series of X-ray diffraction (XRD) (Nuss et al, 2010) has provided valuable data on changes of the separations of the lattice sites. Several studies have investigated XAFS around zinc sites in compounds or complex systems (Gilbert et al, 2002;Chung et al, 2000;Sier et al, 2020). An XAFS study of zinc metal (Rae et al, 2010) yielded too sparse a grid for detailed analysis, though a recent work at room temperature using XERT (Ekanayake et al, 2021a,b;Sier et al, 2022) laid a strong and detailed baseline from which thermal evolution could be investigated.…”