Christopher Chantler

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

Publisher: International Union of Crystallography (IUCr)

Date: 2023

DOI: 10.1107/S1600577522010293

Abstract: The 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 s le. 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.

Vignetted photon fields, recharacterisation of V Kα, and reducing X‐ray uncertainties by a factor of two

Publisher: Wiley

Date: 20-10-2020

DOI: 10.1002/XRS.3207

An absolute energy characterisation of scandium Kβto 2 parts per million

Publisher: IOP Publishing

Date: 25-09-2020

DOI: 10.1088/1361-6455/ABB1FF

High accuracy characterisation for the absolute energy of scandium Kα

Publisher: IOP Publishing

Date: 24-07-2019

DOI: 10.1088/1361-6455/AB29B1

Count‐rate, linearity, and performance of new backgammon detector technology

Publisher: Wiley

Date: 14-02-2019

DOI: 10.1002/XRS.3024

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

Publisher: Wiley

Date: 11-11-2016

DOI: 10.1002/CHEM.201603823

Abstract: Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D

The significance of fluorescence in transmission X‐ray absorption spectroscopy and X‐ray absorption fine structure

Publisher: Wiley

Date: 26-08-2021

DOI: 10.1002/XRS.3262

Abstract: We present a method to explore the effect of fluorescence on X‐ray attenuation measurements obtained from X‐ray absorption spectroscopy (XAS). We use the X‐ray extended range technique‐like method (XERT‐like). The experimental setup includes different sized apertures to control the number of secondary X‐rays entering the detector. Comparison of attenuation measurements produced with different aperture combination permit investigation of the effect of fluorescence radiation. In this work, fluorescence has a large impact on the attenuation measurements of thick zinc foils. The correction is energy‐dependent and s le thickness‐dependent and changes the structure and relative litudes of oscillations in the near‐edge region. Correction for this systematic is important for absolute measurement, for edge‐jump and edge characterization, and for near‐edge structure and litudes. A significant background scattering due to zinc fluorescence from the beamline optics was identified and treated for the first time. The model theory fits the experimental measurements well. The resulting correction is most significant for thicker foils with the 50 μm s le experiencing a shift in attenuation of up to 15.5% for the largest aperture while the 25 and 10 μm s les saw corrections of up to 0.153 and 0.00639% respectively. The standard error from the dispersion and variance was reduced by up to 50.5% after the correction for the 50 μm s le. This enables high‐accuracy data and theoretical and experimental analysis to below 0.03% accuracy. The technology is advanced. There is a cost in preparation and measurement time of less than a factor of two, and the principles are clear and can be routinely implemented on any beamline. This paper focuses on the model and parameters for fluorescence.

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 investigat

Publisher: International Union of Crystallography (IUCr)

Date: 19-07-2021

DOI: 10.1107/S1600577521005981

Abstract: 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.

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

Publisher: International Union of Crystallography (IUCr)

Date: 17-08-2020

DOI: 10.1107/S1600577520010097

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.

Ab initio calculations of Auger electron kinetic energies: Breadth and depth

Publisher: Elsevier BV

Date: 11-2022

DOI: 10.1016/J.RADPHYSCHEM.2022.110472

High-accuracy mass attenuation coefficients and X-ray absorption spectroscopy of zinc – the first X-ray Extended Range Technique-like experiment in Australia

Publisher: International Union of Crystallography (IUCr)

Date: 19-07-2021

DOI: 10.1107/S1600577521005993

Abstract: 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 s les but was still large and significant for thin s les. 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.

Theoretical calculation of characteristic radiation: multiconfiguration Dirac–Hartree–Fock calculations in scandium K α and K

Publisher: IOP Publishing

Date: 06-04-2022

DOI: 10.1088/1361-6455/AC61ED

Abstract: The characteristic x-ray spectra of 3 d transition metals are a constant source of advances in atomic physics, x-ray spectrometry, and quantum mechanics. Prior to this work, there was a discrepancy of 0.549 eV between theoretical and experimental results for the scandium Kα 1 peak energy, representing a 55 σ discrepancy using the experimental uncertainty. This work improves this to a 0.330 eV discrepancy with only a 4 σ error between experiment and theory. Furthermore, we add considerable evidence that asymmetries in x-ray spectra are described by shake events. This work provides ab initio calculations for the diagram and shake-off satellite lines of Sc Kα and Kβ and makes significant improvement on the previous fitting between theory and experiment, from a χ r 2 of 7.35 and 20.85 to 1.60 and 1.45 for Kα and Kβ , respectively. Therefore, we make a strong claim that the asymmetries in scandium x-ray lines exist due to satellite lines with very little room for other hypothesised phenomena to exist, such as Kondo-like interactions and Doniac–Sunjic asymmetries. By fitting to the best experimental data for Sc Kα , β we obtain values for the width and intensity of the satellite lines which enable us to reconstruct the Kα , Kβ profiles.

A new satellite of manganese revealed by extended-range high-energy-resolution fluorescence detection

Publisher: International Union of Crystallography (IUCr)

Date: 07-04-2023

DOI: 10.1107/S1600577523002539

Abstract: The discovery of a new physical process in manganese metal is reported. This process will also be present for all manganese-containing materials in condensed matter. The process was discovered by applying our new technique of XR-HERFD (extended-range high-energy-resolution fluorescence detection), which was developed from the popular high-resolution RIXS (resonant inelastic X-ray scattering) and HERFD approaches. The acquired data are accurate to many hundreds of standard deviations beyond what is regarded as the criterion for `discovery'. Identification and characterization of many-body processes can shed light on the X-ray absorption fine-structure spectra and inform the scientist on how to interpret them, hence leading to the ability to measure the dynamical nanostructures which are observable using the XR-HERFD method. Although the many-body reduction factor has been used universally in X-ray absorption spectroscopy in analysis over the past 30 years (thousands of papers per year), this experimental result proves that many-body effects are not representable by any constant reduction factor parameter. This paradigm change will provide the foundation for many future studies and X-ray spectroscopy.

Cu Kα3,4

Publisher: American Physical Society (APS)

Date: 13-01-2023

DOI: 10.1103/PHYSREVA.107.012809

Discovery Projects - Grant ID: DP0208207

Start Date: 2002

End Date: 12-2006

Amount: $307,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0771096

Start Date: 2008

End Date: 12-2011

Amount: $450,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP120100069

Start Date: 05-2012

End Date: 06-2015

Amount: $165,906.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0451310

Start Date: 01-2004

End Date: 12-2007

Amount: $370,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP210100795

Start Date: 03-2021

End Date: 03-2025

Amount: $498,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0882493

Start Date: 2008

End Date: 12-2008

Amount: $700,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP110101896

Start Date: 07-2011

End Date: 12-2016

Amount: $480,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE110100174

Start Date: 12-2011

End Date: 12-2012

Amount: $800,000.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR0354591

Start Date: 01-2004

End Date: 12-2003

Amount: $10,000.00

Funder: Australian Research Council