A simple correction for the parallax effect in X-ray pair distribution function measurements

Marlton, Frederick P.; Ivashko, Oleh; Zimmerman, M. v.; Gutowski, Olof; Dippel, Ann Christin; Jørgensen, Mads Ry Vogel

doi:10.1107/s1600576719011580

Cited by 7 publications

(8 citation statements)

References 46 publications

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“…Measured intensities should generally be kept well below the saturation levels, as trapped excited states can remain after long periods of high exposure, leading to unwanted features in the pixel response that must be removed . Other considerations may be necessary for other detection technologies such as Si and CdTe hybrid photon counting detectors. , Diffraction images must be calibrated and corrected for polarization, spatial distortions, , unequal pixel response and parasitic scattering effects . It is further important to apply proper masking of the images to remove anomalously dark or bright pixels, dead pixels, discrete diffraction spots caused by a poor powder average, or other effects such as shadows from any equipment located in the cone of diffracted radiation.…”

Section: Experimental Considerationsmentioning

confidence: 99%

Structural Analysis of Molecular Materials Using the Pair Distribution Function

2021

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This is a review of atomic pair distribution function (PDF) analysis as applied to the study of molecular materials. The PDF method is a powerful approach to study short-and intermediate-range order in materials on the nanoscale. It may be obtained from total scattering measurements using X-rays, neutrons, or electrons, and it provides structural details when defects, disorder, or structural ambiguities obscure their elucidation directly in reciprocal space. While its uses in the study of inorganic crystals, glasses, and nanomaterials have been recently highlighted, significant progress has also been made in its application to molecular materials such as carbons, pharmaceuticals, polymers, liquids, coordination compounds, composites, and more. Here, an overview of applications toward a wide variety of molecular compounds (organic and inorganic) and systems with molecular components is presented. We then present pedagogical descriptions and tips for further implementation. Successful utilization of the method requires an interdisciplinary consolidation of material preparation, high quality scattering experimentation, data processing, model formulation, and attentive scrutiny of the results. It is hoped that this article will provide a useful reference to practitioners for PDF applications in a wide realm of molecular sciences, and help new practitioners to get started with this technique.

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Section: Experimental Considerationsmentioning

confidence: 99%

Structural Analysis of Molecular Materials Using the Pair Distribution Function

2021

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“…Specifically, the thickness of the scintillator and the mounting design can have large effects on the magnitude of the parallax and topography distortions introduced by a detector. It has been shown by many published reports that it is necessary to correct these distortions in the traditional geometry in order to measure and analyze X-ray scattering patterns properly (Weiß et al, 2012;Lu ¨thi et al, 2019;Marlton et al, 2019;Wu et al, 2002;Zaleski et al, 1998). Equivalently, it was observed that implementing the PE-1621 in the inclined geometry similarly necessitated distortion corrections for proper measurement and analysis.…”

Section: Resultsmentioning

confidence: 99%

“…In order to achieve the desired counting statistics and fast acquisition times, two-dimensional digital flat-panel area detectors are commonly used when performing X-ray total scattering measurements (Marlton et al, 2019). Traditional detector geometries have the incident X-ray beam normal to the detector surface, as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

An inclined detector geometry for improved X-ray total scattering measurements

et al. 2023

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X-ray total scattering measurements are implemented using a digital flat-panel area detector in an inclined geometry and compared with the traditional geometry. The traditional geometry is defined here by the incident X-ray beam impinging on and normal to the center-most pixel of a detector. The inclined geometry is defined here by a detector at a pitch angle α, set to 15° in this case, bisected by the vertical scattering plane. The detector is positioned such that the incident X-ray beam strikes the pixels along the bottom edge and 90° scattered X-rays impinge on the pixels along the top edge. The geometric attributes of the inclined geometry translate into multiple benefits, such as an extension of the measurable scattering range to 90°, a 47% increase in the accessible magnitudes of the reciprocal-space vector Q and a leveling of the dynamic range in the measured total scattering pattern. As a result, a sixfold improvement in signal-to-noise ratios is observed at higher scattering angles, enabling up to a 36-fold reduction in acquisition time. Additionally, the extent of applied modification functions is reduced, decreasing the magnitude of termination ripples and improving the real-space resolution of the pair distribution function G(r). Taken all together, these factors indicate that the inclined geometry produces higher quality data than the traditional geometry, usable for simultaneous Rietveld refinement and total scattering studies.

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“…The latter is associated with X-ray photons traversing multiple detector pixels at high 2 angles for detectors with thick sensors. Detector parallax also results in peak position and peak shape artefacts; the former can be corrected using a simple quadratic polynomial as demonstrated by Marlton et al (2019).…”

Section: Parallax Artefactmentioning

confidence: 99%

DLSR: a solution to the parallax artefact in X-ray diffraction computed tomography data

Vamvakeros

Coelho²,

Matras³

et al. 2020

J Appl Cryst

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A new tomographic reconstruction algorithm is presented, termed direct least-squares reconstruction (DLSR), which solves the well known parallax problem in X-ray-scattering-based experiments. The parallax artefact arises from relatively large samples where X-rays, scattered from a scattering angle 2θ, arrive at multiple detector elements. This phenomenon leads to loss of physico-chemical information associated with diffraction peak shape and position (i.e. altering the calculated crystallite size and lattice parameter values, respectively) and is currently the major barrier to investigating samples and devices at the centimetre level (scale-up problem). The accuracy of the DLSR algorithm has been tested against simulated and experimental X-ray diffraction computed tomography data using the TOPAS software.

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A simple correction for the parallax effect in X-ray pair distribution function measurements

Cited by 7 publications

References 46 publications

Structural Analysis of Molecular Materials Using the Pair Distribution Function

Structural Analysis of Molecular Materials Using the Pair Distribution Function

An inclined detector geometry for improved X-ray total scattering measurements

DLSR: a solution to the parallax artefact in X-ray diffraction computed tomography data

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