Browsing by Author "Tran, CQ"
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- ItemComplex atomic fine structure in the phase domain: exciting opportunities and challenges(International Union of Crystallography, 2021-08-14) Tran, CQ; Chantler, CT; Kirk, T; Dao, MH; Di Pasquale, P; Ceddia, J; Barnea, Z; de Jonge, MD; Kewish, CMX-ray Absorption Spectroscopy has been one of the most powerful tools for probing atomic and molecular structures of materials. However, the measured fine structures in the absorption domain do not have adequate dimensionalities to extract three-dimensional structural information of the material of interest. A technique that allows accurate measurements of atomic fine structure in both the absorption and phase domains will open exciting opportunities in a wide range of fundamental and applied research. In this presentation, we will describe a new technique for determining simultaneously the real and imaginary components of the complex atomic form factor. The technique used Fourier Transform Holography with an extended reference and applicable to both crystalline and amorphous samples. Details of an application of the technique in spectroscopy mode to obtain the X-ray Complex Fine Structure across the copper K-edge will be discussed. © The Authors
- ItemHigh-accuracy determination of photoelectric cross sections, X-ray absorption fine structure and nanostructure analysis of zinc selenide using the X-ray extended range technique(International Union of Crystallography, 2021-08-14) Sier, D; Cousland, GP; Trevorah, RM; Ekanayake, RSK; Tran, CQ; Hester, JR; Chantler, CTMeasurements 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 (XERT), a relatively new methodology, which can be set up on most synchrotron X-ray beamlines. 561 attenuation coefficients were recorded in the energy range of 6.8 keV to 15 keV that was independently calibrated using powder diffractometry, with measurements concentrated at the zinc and selenium pre-edge, near edge and fine structure absorption edge regions. The removal of systematic effects as well as coherent (Thermal Diffuse) and incoherent (Compton) scattering processes produced very high accuracy values of photoelectrc attenuation which in turn yielded a 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 to theoretically determined values of the attenuation showing discrepancies from literature theory of up to 4%, motivating further investigation into the origin of such discrepancies. © The Authors
- ItemHigh-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique(International Union of Crystallography, 2022-10-24) John, MW; Sier, D; Ekanayake, RSK; Schalken, MJ; Tran, CQ; Johannessen, B; de Jonge, MD; Kappen, P; Chantler, CTThe most accurate measurements of the mass attenuation coefficient for metals at low temperature for the zinc K-edge from 9.5 keV to 11.5 keV at temperatures of 10 K, 50 K, 100 K and 150 K using the hybrid technique are reported. This is the first time transition metal X-ray absorption fine structure (XAFS) has been studied using the hybrid technique and at low temperatures. This is also the first hybrid-like experiment at the Australian Synchrotron. The measured transmission and fluorescence XAFS spectra are compared and benchmarked against each other with detailed systematic analyses. A recent method for modelling self-absorption in fluorescence has been adapted and applied to a solid sample. The XAFS spectra are analysed using eFEFFIT to provide a robust measurement of the evolution of nanostructure, including such properties as net thermal expansion and mean-square relative displacement. This work investigates crystal dynamics, nanostructural evolution and the results of using the Debye and Einstein models to determine atomic positions. Accuracies achieved, when compared with the literature, exceed those achieved by both relative and differential XAFS, and represent a state-of-the-art for future structural investigations. Bond length uncertainties are of the order of 20–40 fm. © Open Access - CC BY 4.0 licence
- ItemHigh‐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(International Union of Crystallography (IUCr), 2021-09-01) Ekanayake, RSK; Chantler, CT; Sier, D; Schalken, MJ; Illig, AJ; de Jonge, MD; Johannessen, B; Kappen, P; Tran, CQHigh-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. © International Union of Crystallography.
- ItemSimultaneous reconstruction and structural fitting of the complex atomic fine structure of copper and iron(Australian Institute of Physics, 2022-12-11) Di Pasquale, P; Tran, CQ; Chantler, CT; Barnea, Z; Kirk, T; Dao, MN; Balaur, E; van Riessen, GA; Hinsley, GN; Jallandhra, A; Ceddia, J; Rogers, J; Kewish, CM; Paterson, DJ; Reinhardt, J; Kirby, N; Mudie, STA novel technique for determining complex atomic fine structure will be described. Exciting applications of the technique such as a phase analogue to x-ray absorption fine structure applications will also be discussed.
- ItemX-ray mass attenuation coefficients and imaginary components of the atomic form factor of zinc over the energy range of 7.2-15.2 keV(American Physical Society, 2010-02) Rae, NA; Chantler, CT; Barnea, Z; de Jonge, MD; Tran, CQ; Hester, JRThe x-ray mass attenuation coefficients of zinc are measured in a high-accuracy experiment between 7.2 and 15.2 keV with an absolute accuracy of 0.044% and 0.197%. This is the most accurate determination of any attenuation coefficient on a bending-magnet beamline and reduces the absolute uncertainty by a factor of 3 compared to earlier work by advances in integrated column density determination and the full-foil mapping technique described herein. We define a relative accuracy of 0.006%, which is not the same as either the precision or the absolute accuracy. Relative accuracy is the appropriate parameter for standard implementation of analysis of near-edge spectra. Values of the imaginary components f″ of the x-ray form factor of zinc are derived. Observed differences between the measured mass attenuation coefficients and various theoretical calculations reach a maximum of about 5% at the absorption edge and up to 2% further than 1 keV away from the edge. The measurements invite improvements in the theoretical calculations of mass attenuation coefficients of zinc. © 2010, American Physical Society