Christopher Chantler - Academia.edu (original) (raw)

Uploads

Papers by Christopher Chantler

Research paper thumbnail of High-accuracy Ni-doped borate glass comparison using X-ray extended-range technique

Acta Crystallographica Section A Foundations and Advances, 2017

Research paper thumbnail of Special Issue on Future Directions in Atomic and Condensed Matter Research and Applications

Radiation Physics and Chemistry

Research paper thumbnail of High-accuracy X-ray absorption spectra from mMsolutions of nickel (II) complexes with multiple solutions using transmission XAS

Journal of Synchrotron Radiation, 2015

A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absol... more A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X-ray absorption fine structure (XAFS) along the lines of the high-accuracy X-ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N-n-propyl-salicylaldiminato) nickel(II) and bis(N-i-propyl-salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mMand 1.5 mMdilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X-ray absorption near-edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordinatio...

Research paper thumbnail of Quantitative determination of major systematics in synchrotron x‐ray experiments: seeing through harmonic components

X-Ray Spectrometry, 2003

In line with an ongoing programme to determine accurately x‐ray attenuation coefficients, we have... more In line with an ongoing programme to determine accurately x‐ray attenuation coefficients, we have developed a method for the quantitative determination of the effect on experimental results of monochromator harmonic components in a synchrotron beam. The technique can be adapted to suit a wide variety of experiments, and is of particular interest because it determines the effect of the harmonic components directly. This avoids the necessity for modelling and is therefore robust. Results of a direct determination of the effect of harmonic components illustrate the power of the technique. We extended the technique to quantify the effects of dark current‐induced errors. Copyright © 2003 John Wiley & Sons, Ltd.

Research paper thumbnail of FDMX: extended X-ray absorption fine structure calculations using the finite difference method

Journal of Synchrotron Radiation, 2016

A new theoretical approach and computational package,FDMX, for general calculations of X-ray abso... more A new theoretical approach and computational package,FDMX, for general calculations of X-ray absorption fine structure (XAFS) over an extended energy range within a full-potential model is presented. The final-state photoelectron wavefunction is calculated over an energy-dependent spatial mesh, allowing for a complete representation of all scattering paths. The electronic potentials and corresponding wavefunctions are subject to constraints based on physicality and self-consistency, allowing for accurate absorption cross sections in the near-edge region, while higher-energy results are enabled by the implementation of effective Debye–Waller damping and new implementations of second-order lifetime broadening. These include inelastic photoelectron scattering and, for the first time, plasmon excitation coupling. This is the first full-potential package available that can calculate accurate XAFS spectra across a complete energy range within a single framework and without fitted paramete...

Research paper thumbnail of Measurement of Mass Absorption Coefficients in Air by Application of Detector Linearity Tests

Research paper thumbnail of XAS structural insights into Cu binding with amyloid Aβ4-y peptides

Acta Crystallographica Section A, 2017

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the presenc... more Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the presence of amyloid (Aß) plaques. In addition to modulating senile Aß plaque formation, Aß-Cu complexes are involved in extensive redox chemical reactions. The first protein sequencing studies of the Aβ plaque core (APC) of AD patients identified NH2-terminal heterogeneity and the majority (64%) of the APC-AD Aß peptides begins with a Phe4 residue. This N-truncated sequence produced the highaffinity (dissociation Kd of femtoM ) amino-terminal Cu Ni (ATCUN, H2N-Xaa–Yaa–His) binding motif.

Research paper thumbnail of Dominance of eclipsed ferrocene conformer in solutions revealed by the IR spectra between 400 and 500 cm-1

Radiation Physics and Chemistry

Research paper thumbnail of Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x-ray spectrometer

ABSTRACT Earlier investigations using the LLNL Spectrometer have revealed several limitations to ... more ABSTRACT Earlier investigations using the LLNL Spectrometer have revealed several limitations to the resolution of observed spectral lines. The first is the broadening due to the finite target source, together with secondary effects due to the bowing of the target. Other limitations relate to the target and spectrometer geometry, and in particular to the small (2R = 30cm) Rowland Circle radius. At small radii the production of a perfect curvature becomes increasingly difficult as distortions of the mosaic spread of crystallite angles are introduced by the stress. This is particularly true of lattice planes with three non-zero Miller indices (e.g., Si111 compared to Si220) and of stiff or thick crystals (e.g., silicon and quartz, which will shatter if greater than 0.2mm crystals are bent to this radius), but small broadening and asymmetrical shifts are also introduced for other crystals. Conversely, soft crystals (such as thin PET) will bend readily to the radius but distort and relax in mountings with fixed bending forces. A set of improvements to the bending techniques for both soft and stiff crystals is addressed. The first and most important development is the use of parallel, vertical posts and (symmetrical) bending points driven by micrometers instead of the earlier formed (i.e., pressed) crystals. The primary advantage is that the curvature from a small number of stress points is calculable, reproducible and does not introduce random stresses and distortions over the surface. The major methods used include the 2-point, 2-bar mount and the 4-point, 4-bar method. Various 4-point, 2-bar methods were also used.

Research paper thumbnail of X-ray measurements in helium-like atoms increased discrepancy between experiment and theoretical QED

Research paper thumbnail of A call for a round robin study of XAFS stability and platform dependence at synchrotron beamlines on well defined samples

Journal of synchrotron radiation, 2018

Round robin studies have been used across fields of science for quality control testing and to in... more Round robin studies have been used across fields of science for quality control testing and to investigate laboratory dependencies and cross-platform inconsistencies as well as to drive forward the improvement of understanding of experimental systems, systematic effects and theoretical limitations. Here, following the Q2XAFS Workshop and Satellite to IUCr Congress 2017 on `Data Acquisition, Treatment, Storage - quality assurance in XAFS spectroscopy', a mechanism is suggested for a suitable study across XAFS (X-ray absorption fine-structure) beamlines and facilities, to enable each beamline to cross-calibrate, provide representative test data, and to enable collaborative cross-facility activities to be more productive.

Research paper thumbnail of Atomic and Solid State Theory, Experiment and Application in X-ray Physics: Proceedings of the 20th International Conference on X-ray and Inner-Shell Processes, July 4–8 2005, Melbourne, Australia

Radiation Physics and Chemistry

Research paper thumbnail of The effects of cosmic ray filtering on low intensity X-ray CCD data

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Various methods exist to filter cosmic rays from X-ray CCD images with weak X-ray spectra. Distor... more Various methods exist to filter cosmic rays from X-ray CCD images with weak X-ray spectra. Distortions of the characteristics of a spectral profile such as peak centroid and relative integrated peak intensities must be kept to a minimum. Optimum methods are those minimising error bars and widths on the final centroid determination and on relative intensities which remain consistent with

Research paper thumbnail of New theoretical investigation resolving discrepancies of atomic form factors and attenuation coefficients in the near-edge soft X-ray regime

Radiation Physics and Chemistry

Research paper thumbnail of The X-ray extended range technique for high-accuracy XAS for comparison and improvement to theoretical modeling

Acta Crystallographica Section A Foundations of Crystallography

Research paper thumbnail of Ferrocene and fluorescence studies: how can we understand stereochemistry of dilute systems?

Acta Crystallographica Section A Foundations of Crystallography

Research paper thumbnail of Atomic form factors and photoelectric absorption cross-sections near absorption edges in the soft X-ray region

AIP Conference Proceedings, 2003

Research paper thumbnail of Richard Day Deslattes, 21 Sept 1931 – 16 May 2001: Calibration of light, matter and fundamental constants

AIP Conference Proceedings, 2003

Research paper thumbnail of Am ethod to determine the absolute harmonic content of an X-ray beam using attenuation measurements

Research paper thumbnail of Conformation Analysis of Ferrocene and Decamethylferrocene via Full-Potential Modelling of XANES and XAFS Spectra

The journal of physical chemistry letters, Jan 8, 2016

Recent high-accuracy x-ray absorption measurements of the sandwich organometallics ferrocene (Fc)... more Recent high-accuracy x-ray absorption measurements of the sandwich organometallics ferrocene (Fc) and decamethylferrocene (DmFc) at temperatures close to liquid helium are compared with new full-potential modelling of x-ray absorption fine structure (XAFS) covering the near-edge region (XANES) and above up to k=7/Å. The implementation of optimised calculations of the oscillatory part of the spectrum from the package FDMX allows detailed study of the spectra in regions of the photoelectron momentum most sensitive to differences in the molecular stereochemistry. For Fc and DmFc, this corresponds to the relative rotation of the cyclopentadienyl rings. When applied to high-accuracy XAFS of Fc and DmFc, the FDMX theory gives clear evidence for the eclipsed conformation for Fc and the staggered conformation for DmFc for frozen solutions at circa 15 K. This represents the first clear experimental assignment of the solution structures of Fc and DmFc and reveals the potential of high-accurac...

Research paper thumbnail of High-accuracy Ni-doped borate glass comparison using X-ray extended-range technique

Acta Crystallographica Section A Foundations and Advances, 2017

Research paper thumbnail of Special Issue on Future Directions in Atomic and Condensed Matter Research and Applications

Radiation Physics and Chemistry

Research paper thumbnail of High-accuracy X-ray absorption spectra from mMsolutions of nickel (II) complexes with multiple solutions using transmission XAS

Journal of Synchrotron Radiation, 2015

A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absol... more A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X-ray absorption fine structure (XAFS) along the lines of the high-accuracy X-ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N-n-propyl-salicylaldiminato) nickel(II) and bis(N-i-propyl-salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mMand 1.5 mMdilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X-ray absorption near-edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordinatio...

Research paper thumbnail of Quantitative determination of major systematics in synchrotron x‐ray experiments: seeing through harmonic components

X-Ray Spectrometry, 2003

In line with an ongoing programme to determine accurately x‐ray attenuation coefficients, we have... more In line with an ongoing programme to determine accurately x‐ray attenuation coefficients, we have developed a method for the quantitative determination of the effect on experimental results of monochromator harmonic components in a synchrotron beam. The technique can be adapted to suit a wide variety of experiments, and is of particular interest because it determines the effect of the harmonic components directly. This avoids the necessity for modelling and is therefore robust. Results of a direct determination of the effect of harmonic components illustrate the power of the technique. We extended the technique to quantify the effects of dark current‐induced errors. Copyright © 2003 John Wiley & Sons, Ltd.

Research paper thumbnail of FDMX: extended X-ray absorption fine structure calculations using the finite difference method

Journal of Synchrotron Radiation, 2016

A new theoretical approach and computational package,FDMX, for general calculations of X-ray abso... more A new theoretical approach and computational package,FDMX, for general calculations of X-ray absorption fine structure (XAFS) over an extended energy range within a full-potential model is presented. The final-state photoelectron wavefunction is calculated over an energy-dependent spatial mesh, allowing for a complete representation of all scattering paths. The electronic potentials and corresponding wavefunctions are subject to constraints based on physicality and self-consistency, allowing for accurate absorption cross sections in the near-edge region, while higher-energy results are enabled by the implementation of effective Debye–Waller damping and new implementations of second-order lifetime broadening. These include inelastic photoelectron scattering and, for the first time, plasmon excitation coupling. This is the first full-potential package available that can calculate accurate XAFS spectra across a complete energy range within a single framework and without fitted paramete...

Research paper thumbnail of Measurement of Mass Absorption Coefficients in Air by Application of Detector Linearity Tests

Research paper thumbnail of XAS structural insights into Cu binding with amyloid Aβ4-y peptides

Acta Crystallographica Section A, 2017

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the presenc... more Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the presence of amyloid (Aß) plaques. In addition to modulating senile Aß plaque formation, Aß-Cu complexes are involved in extensive redox chemical reactions. The first protein sequencing studies of the Aβ plaque core (APC) of AD patients identified NH2-terminal heterogeneity and the majority (64%) of the APC-AD Aß peptides begins with a Phe4 residue. This N-truncated sequence produced the highaffinity (dissociation Kd of femtoM ) amino-terminal Cu Ni (ATCUN, H2N-Xaa–Yaa–His) binding motif.

Research paper thumbnail of Dominance of eclipsed ferrocene conformer in solutions revealed by the IR spectra between 400 and 500 cm-1

Radiation Physics and Chemistry

Research paper thumbnail of Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x-ray spectrometer

ABSTRACT Earlier investigations using the LLNL Spectrometer have revealed several limitations to ... more ABSTRACT Earlier investigations using the LLNL Spectrometer have revealed several limitations to the resolution of observed spectral lines. The first is the broadening due to the finite target source, together with secondary effects due to the bowing of the target. Other limitations relate to the target and spectrometer geometry, and in particular to the small (2R = 30cm) Rowland Circle radius. At small radii the production of a perfect curvature becomes increasingly difficult as distortions of the mosaic spread of crystallite angles are introduced by the stress. This is particularly true of lattice planes with three non-zero Miller indices (e.g., Si111 compared to Si220) and of stiff or thick crystals (e.g., silicon and quartz, which will shatter if greater than 0.2mm crystals are bent to this radius), but small broadening and asymmetrical shifts are also introduced for other crystals. Conversely, soft crystals (such as thin PET) will bend readily to the radius but distort and relax in mountings with fixed bending forces. A set of improvements to the bending techniques for both soft and stiff crystals is addressed. The first and most important development is the use of parallel, vertical posts and (symmetrical) bending points driven by micrometers instead of the earlier formed (i.e., pressed) crystals. The primary advantage is that the curvature from a small number of stress points is calculable, reproducible and does not introduce random stresses and distortions over the surface. The major methods used include the 2-point, 2-bar mount and the 4-point, 4-bar method. Various 4-point, 2-bar methods were also used.

Research paper thumbnail of X-ray measurements in helium-like atoms increased discrepancy between experiment and theoretical QED

Research paper thumbnail of A call for a round robin study of XAFS stability and platform dependence at synchrotron beamlines on well defined samples

Journal of synchrotron radiation, 2018

Round robin studies have been used across fields of science for quality control testing and to in... more Round robin studies have been used across fields of science for quality control testing and to investigate laboratory dependencies and cross-platform inconsistencies as well as to drive forward the improvement of understanding of experimental systems, systematic effects and theoretical limitations. Here, following the Q2XAFS Workshop and Satellite to IUCr Congress 2017 on `Data Acquisition, Treatment, Storage - quality assurance in XAFS spectroscopy', a mechanism is suggested for a suitable study across XAFS (X-ray absorption fine-structure) beamlines and facilities, to enable each beamline to cross-calibrate, provide representative test data, and to enable collaborative cross-facility activities to be more productive.

Research paper thumbnail of Atomic and Solid State Theory, Experiment and Application in X-ray Physics: Proceedings of the 20th International Conference on X-ray and Inner-Shell Processes, July 4–8 2005, Melbourne, Australia

Radiation Physics and Chemistry

Research paper thumbnail of The effects of cosmic ray filtering on low intensity X-ray CCD data

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Various methods exist to filter cosmic rays from X-ray CCD images with weak X-ray spectra. Distor... more Various methods exist to filter cosmic rays from X-ray CCD images with weak X-ray spectra. Distortions of the characteristics of a spectral profile such as peak centroid and relative integrated peak intensities must be kept to a minimum. Optimum methods are those minimising error bars and widths on the final centroid determination and on relative intensities which remain consistent with

Research paper thumbnail of New theoretical investigation resolving discrepancies of atomic form factors and attenuation coefficients in the near-edge soft X-ray regime

Radiation Physics and Chemistry

Research paper thumbnail of The X-ray extended range technique for high-accuracy XAS for comparison and improvement to theoretical modeling

Acta Crystallographica Section A Foundations of Crystallography

Research paper thumbnail of Ferrocene and fluorescence studies: how can we understand stereochemistry of dilute systems?

Acta Crystallographica Section A Foundations of Crystallography

Research paper thumbnail of Atomic form factors and photoelectric absorption cross-sections near absorption edges in the soft X-ray region

AIP Conference Proceedings, 2003

Research paper thumbnail of Richard Day Deslattes, 21 Sept 1931 – 16 May 2001: Calibration of light, matter and fundamental constants

AIP Conference Proceedings, 2003

Research paper thumbnail of Am ethod to determine the absolute harmonic content of an X-ray beam using attenuation measurements

Research paper thumbnail of Conformation Analysis of Ferrocene and Decamethylferrocene via Full-Potential Modelling of XANES and XAFS Spectra

The journal of physical chemistry letters, Jan 8, 2016

Recent high-accuracy x-ray absorption measurements of the sandwich organometallics ferrocene (Fc)... more Recent high-accuracy x-ray absorption measurements of the sandwich organometallics ferrocene (Fc) and decamethylferrocene (DmFc) at temperatures close to liquid helium are compared with new full-potential modelling of x-ray absorption fine structure (XAFS) covering the near-edge region (XANES) and above up to k=7/Å. The implementation of optimised calculations of the oscillatory part of the spectrum from the package FDMX allows detailed study of the spectra in regions of the photoelectron momentum most sensitive to differences in the molecular stereochemistry. For Fc and DmFc, this corresponds to the relative rotation of the cyclopentadienyl rings. When applied to high-accuracy XAFS of Fc and DmFc, the FDMX theory gives clear evidence for the eclipsed conformation for Fc and the staggered conformation for DmFc for frozen solutions at circa 15 K. This represents the first clear experimental assignment of the solution structures of Fc and DmFc and reveals the potential of high-accurac...