Laboratory Bench-Top EXAFS with STJ Spectrometer

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PROJECT SUMMARY Extended X-ray absorption fine structure (EXAFS) spectroscopy is a technique that gives element-specific structural and chemical information about molecules. An enormous advantage of EXAFS spectroscopy is that it is readily applied to many different kinds of sample, including, solutions, powders, slurries, and animal tissues. Current EXAFS instruments require bright X-ray beams from specialized synchrotron lightsources for most samples, meaning that access is limited to priority research and the science that can be done is restricted by the need to work at remote sites as well as the often months-long wait for access. STAR Cryoelectronics intends to build a laboratory instrument to measure transmission EXAFS spectra to the same precision typically measured at synchrotron radiation sources and with comparable signal-to-noise. This project will involve improved energy-resolving X-ray detectors based on superconducting tunnel junctions (STJs) to achieve the energy resolution and efficiency needed to make EXAFS measurements feasible in a regular laboratory setting. The first aim is a plan to design and fabricate novel STJ detector chips for these next-generation X-ray detectors. STAR Cryoelectronics will build on previous success with tantalum-based STJs to produce novel aluminum junctions with tantalum absorbers capable of functioning to energies up to at least 11,000 eV. This part of the project will involve extensive testing as we refine the design and fabrication parameters. A second aim is to couple this new STJ detector with a sample chamber and broadband X-ray source to a complete, user-friendly EXAFS instrument. Associated with second aim is a significant software development project, intended to provide the end user an easy-to-use instrument. This will include instrument control, processing of EXAFS data in real-time during data acquisition, and the ability to analyze data during data acquisition. This latter ability should not only provide preliminary results, but allow assessment of data and sample quality, thereby optimizing instrument time. This project’s ultimate aim is to make EXAFS a routine laboratory technique, alongside more well-known spectroscopies such as UV-visible spectroscopy, IR spectroscopy, and NMR spectroscopy. While the proposed laboratory transmission EXAFS instrument should be complementary to synchrotron lightsource based EXAFS, it should nonetheless reduce the need to apply for access to synchrotrons for EXAFS, open up the technique for more general and routine chemical and biological applications, and enable new scientific opportunities and novel spectroscopic applications. 1