National Synchrotron Light Source Seminar

There are numerous important scientific applications of core-level emission-mode x-ray spectroscopies. These are generally based on the direct determination of the valence, spin state, and local electronic structure of the target species, and often make use of the suppression of spectral broadening from the short core-hole lifetimes. However, traditional hard x-ray emission spectrometers based on spherically-bent crystal analyzers (SBCA’s) pose some practical difficulties. These include their engineering complexity and expense, the low collection solid angles of SBCA’s, and also the difficulties coordinating such major instrumentation with other apparatus required for the preparation of extreme sample conditions. It is important to recognize that the use of SBCA’s as the dispersing optic originates with some of the earliest work in high-resolution x-ray spectroscopy from the 1930’s, which was itself inspired by curved optical gratings originating in the 1890’s work of Henry Rowland. In other words, there is no particular reason to think that SBCA’s are the only, or the optimal, general purpose approach for modern synchrotron-based studies of x-ray emission. In two recent papers my group has demonstrated that an appropriate collection of small, flat crystals placed quite near to the sample can be a useful dispersive optic for XES and related emission-mode x-ray spectroscopies. The resulting short-working distance (SWD) x-ray spectrometers are compact, portable, easy to use, and typically cost only a few thousand dollars to fabricate. They also often equal or outperform traditional large-scale XES/IXS instruments based on SBCA’s. Less than a year after the first development of SWD x-ray optics, it is reasonable to project that this technology will have interesting applications in high-pressure science, actinide chemistry, catalyst chemistry, battery electrode research, and ultrafast time-resolved studies of photochemistry.