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A new strategy is presented to reduce primary X-ray damage in macromolecular crystallography. The strategy is based on separating the diffracting and damaged regions as much as feasible. The source of the radiation damage to macromolecular crystals is from two primary mechanisms: the direct excitations of electrons by absorption, and inelastic scattering of the X-rays. The first produces photoelectrons with their accompanying Auger electrons from relaxation of the core hole and the second creates Compton electrons. The properties of these two mechanisms and calculations of primary X-ray damage quantify how to modify the spatial distribution of X-rays to reduce the deleterious effects of radiation damage. By focusing the incident X-rays into vertical stripes, it is estimated that the survival (the time during which quality diffraction data can be obtained with a given X-ray flux) of large crystals can be increased by at least a factor of 1.6, while for very small platelet crystals the survival can be increased by up to a factor of 14.

Spherically bent crystal analyzers (SBCAs) are the dominant high-resolution hard X-ray optic in the ongoing rebirth of laboratory-based X-ray absorption fine structure (XAFS) and X-ray emission spectroscopy (XES) as well as in synchrotron methods such as high energy resolution fluorescence detection (HERFD) and non-resonant X-ray Raman scattering (XRS). In the overwhelming majority of cases, SBCAs are implemented in a 'symmetric' configuration on the Rowland circle, wherein the diffracting crystal plane is nominally coincident with the analyzer surface. We report here comprehensive investigations of 'asymmetric' operation of SBCA on the Rowland circle, wherein the diffracting crystal plane is not coincident with the optical surface of the analyzer. First, we have developed a laboratory spectrometer for XAFS and XES that is specialized for asymmetric SBCA operation. We find several benefits, including the capacity to use a single SBCA over a very wide energy range via 'hkl hopping' and the frequent ability to eliminate Johann error, the most prevalent energy-broadening mechanism when using SBCA symmetrically on the Rowland circle. Second, we expand these ideas to synchrotron facilities with a demonstration study of HERFD and XRS where asymmetric operation also provided advantage. Our results suggest that large-array systems for HERFD augmented with an additional mechanical degree of freedom could streamline user operation and also indicate benefits to XRS in the asymmetric configuration, where larger solid angle, larger sample-to-detector distance, and decreased Johann error can be achieved simultaneously. [ABSTRACT FROM AUTHOR]

Spherically‐bent crystal analyzers (SBCAs) see considerable use in very high‐resolution hard X‐ray wavelength dispersive X‐ray fluorescence spectroscopy, often called X‐ray emission spectroscopy (XES). While Si and Ge are the most frequently used diffractive components of SBCAs, we consider here the somewhat classical choice of muscovite mica as the dispersing element. We find that the various harmonics of a highest‐quality mica‐based SBCA show ~5–~40% of the integral reflectivity per unit solid angle of a typical Si or Ge SBCA in the hard X‐ray range, and that the mica SBCA have comparable energy resolution to the traditional SBCAs. Interestingly, the choice of mica comes with a practical benefit: the primary (0,0,2) reflection has sufficiently strong harmonics that are fairly tightly spaced in energy so that they span the complete energy range from ~4 to ~11 keV when used at convenient Bragg angles in a Rowland circle spectrometer. Hence, a single mica SBCA can be used for every K‐shell emission line of three dimensional transition metals and every L‐shell emission line of the lanthanide elements simply by selecting the correct mica (0,0,2) harmonic with a final energy‐dispersive solid state detector. The loss in efficiency is counteracted by an operational efficiency, i.e., the "universal" application of a single analyzer over a very large range of elements. This performance suggests future application of mica SBCAs in both laboratory‐based XES and synchrotron‐based photon‐in, photon‐out spectroscopies in the hard X‐ray range. [ABSTRACT FROM AUTHOR]

There are more than 100 beamlines or endstations worldwide that frequently support X‐ray absorption fine‐structure (XAFS) measurements, thus providing critical enabling capability for research across numerous scientific disciplines. However, the absence of a supporting tier of more readily accessible, lower‐performing options has caused systemic inefficiencies, resulting in high oversubscription and the omission of many scientifically and socially valuable XAFS applications that are incompatible with the synchrotron facility access model. To this end, this work describes the design, performance and uses of the Clean Energy Institute X‐ray absorption near‐edge structure (CEI‐XANES) laboratory spectrometer and its use as both a user‐present and mail‐in facility. Such new additions to the XAFS infrastructure landscape raise important questions about the most productive interactions between synchrotron radiation and laboratory‐based capabilities; this can be discussed in the framework of five categories, only one of which is competitive. The categories include independent operation on independent problems, use dictated by convenience, pre‐synchrotron preparatory use of laboratory capability, post‐synchrotron follow‐up use of laboratory capability, and parallel use of both synchrotron radiation and laboratory systems. [ABSTRACT FROM AUTHOR]

X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced x-ray spectroscopies that impact a wide range of disciplines. However, unlike the majority of other spectroscopic methods, XAFS and XES are accompanied by an unusual access model, wherein the dominant use of the technique is for premier research studies at world-class facilities, i.e., synchrotron x-ray light sources. In this paper, we report the design and performance of an improved XAFS and XES spectrometer based on the general conceptual design of Seidler et al. [Rev. Sci. Instrum. 85, 113906 (2014)]. New developments include reduced mechanical degrees of freedom, much-increased flux, and a wider Bragg angle range to enable extended x-ray absorption fine structure (EXAFS) measurement and analysis for the first time with this type of modern laboratory XAFS configuration. This instrument enables a new class of routine applications that are incompatible with the mission and access model of the synchrotron light sources. To illustrate this, we provide numerous examples of x-ray absorption near edge structure (XANES), EXAFS, and XES results for a variety of problems and energy ranges. Highlights include XAFS and XES measurements of battery electrode materials, EXAFS of Ni with full modeling of results to validate monochromator performance, valence-to-core XES for 3d transition metal compounds, and uranium XANES and XES for different oxidation states. Taken en masse, these results further support the growing perspective that modern laboratory-based XAFS and XES have the potential to develop a new branch of analytical chemistry. [ABSTRACT FROM AUTHOR]

High-resolution x-ray emission spectroscopy (XES) has recently been demonstrated in the laboratory setting, achieving nearly synchrotron-level count rates despite the use of only conventional x-ray tube sources. This development holds high potential for expanding the reach of x-ray spectroscopies beyond the specialist community of synchrotron users, but comes with its own unique technical challenges for instrument performance and also, just as importantly, for ease of use by non-experts in x-ray science. Here, we address spectrometer design and operations in the context of the imperfect parallelness between the desired crystal plane and the wafer surface in spherically bent crystal analyser (SBCAs), an effect usually called “wafer miscut”. This introduces an ambiguous re-focusing error that typically requires a motorized two-axis tilt stage for fine alignment of the SBCA optic onto the ideal Rowland circle configuration. We instead demonstrate an asymmetric Rowland geometry that eliminates all need for motorized fine-tilt adjustment. We find rapid, extremely reproducible re-insertion of any aligned SBCA, i.e., without the need for any subsequent reoptimization. These improvements strongly benefit the ease of use of laboratory based spectrometers, taking them an important step closer to the level of turnkey operations needed for wide adoption outside of the existing specialist community. [ABSTRACT FROM AUTHOR]

• Fe K-edge XANES established the Fe redox distribution of several silicates. • Fe Kβ XES showed muted redox sensitivity for silicate-based minerals and glasses. • DFT revealed the XES results are consistent with excited state charge transfers. There is considerable need for robust, accessible, and non-destructive Fe redox analysis methods for silicate-based minerals and glasses. A popular method assigns the distribution of Fe2+ and Fe3+ atoms using pre-edge features in the Fe K-edge X-ray absorption near edge structure (XANES). We expand on this work in two ways. First, we use XANES to assign the Fe redox distribution in four silicate materials: two geological reference materials and two industrial glasses. This example highlights the effect of the Fe atomic environment on pre-edge features' intensities and stresses the need for specifically developed calibration curves. We then investigate Fe Kβ X-ray emission spectroscopy as an independent complement for redox assignments. Here, the silicates do not show a systematic dependence on oxidation state. This is explored with electronic structure calculations, which support previous claims that the lack of sensitivity is due to charge transfers following creation of the 1s core hole. [ABSTRACT FROM AUTHOR]