Exposure strategies for higher-quality pair distribution function analysis: patching saturated peak intensities

Le résumé fourni par la source

Quantitative pair distribution function (PDF) analysis requires accurate measurement of both intense Bragg reflections and weak diffuse scattering. Optimizing the exposure of the integrating area detector, such as the amorphous-silicon flat-panel detectors often used for PDF measurements, is a compromise between avoiding saturation and achieving sufficient signal-to-noise ratio at high scattering angles. Here, the errors introduced by both under- and over-exposing total scattering data are illustrated, including how these exposure conditions propagate into the corresponding PDF data. Practical ways to mitigate these effects are presented, including a strategy to restore intensity for saturated peaks in over-exposed images. This restoration method is provided as an automated utility, PDF Patch , which applies the scaling, resolution matching and selective substitution steps needed for consistent treatment of datasets with saturated or near-saturated ( i.e. within a non-linear detector response regime) intensities. The approach merges long-exposure data, which provide high signal-to-noise ratios for weak scattering, with short screening exposure or complementary diffraction measurements that preserve unsaturated peak intensities. When this strategy is applied to example data for TiO 2 and MOF-808 metal–organic framework materials, the restored datasets yield higher-quality PDFs with lower noise and smaller residuals to the fits than standard data. Beyond recovering accidentally over-exposed measurements, this `data-healing' approach enables intentional over-exposure as an efficient means to extend the usable dynamic range of area detectors and to improve PDF quality more effectively than averaging more frames.

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