Applications of Asymmetric Rowland Geometries in Hard X-ray Spectroscopies

Abstract

Hard X-ray spectroscopy is widely used to characterize all states of matter in contemporary and relevant materials systems including but not limited to life sciences, catalyst materials, batteries and energy storage materials, pharmaceuticals, nuclear fuel and waste, and fossil fuels. At the core of these spectroscopy techniques is the measurement of X-ray absorption fine structure (XAFS), and the secondary process of X-ray fluorescence.Both laboratory and synchrotron hard X-ray spectroscopies demand the use of high-resolution spectrometers to analyze scattered or fluorescing photons. In the laboratory, spectrometers are required for the measurement of both XAFS and X-ray emission spectroscopy (XES). At synchrotron light sources, advanced photon-in/photon-out techniques such as high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS), resonant inelastic X-ray scattering (RIXS) / resonant XES, and X-ray Raman Scattering (XRS) all require the use of a spectrometer to analyze outgoing photons. Across all of these disciplines, the state-of-the-art for large collection solid angles and point-focusing geometries for efficient data collection at high resolution rely on the same diffractive optic: the spherically bent crystal analyzer (SBCA). The employment of SBCAs for high energy resolution photon analysis across this suite of spectroscopy techniques are in the same symmetric geometry. The work within this dissertation details the characterization, commissioning, and application of asymmetric Rowland geometries of SBCAs to XAFS/XES, HERFD, and XRS. I propose that this is an overlooked and underutilized modality for spectrometer design and that it frequently enables improved energy resolution and a massively increased energy range for photon analysis; addressing the two largest shortcomings of SBCAs in conventional symmetric geometries. Most importantly, the use of SBCAs in asymmetric Rowland geometries can drastically reduce the number of unique optics required for a sufficient analysis energy range. I detail the applications of this geometry in the design and construction of three separate spectrometers (laboratory XAFS/XES, synchrotron HERFD, synchrotron XRS), and in all three cases we find that it is lowering the resource barrier required for these techniques. The relevance of these developments for materials science research is substantial, and some representative applications are discussed and presented.