This award from the Chemistry Research Instrumentation and Facilities (CRIF) Program and the Major Research Instrumentation (MRI) Program of the Office of Integrative Activities will support the development of an accurate and reliable anomalous x-ray diffraction (AXD) spectrometer consisting of a high-energy-resolution narrow-band-pass crystal-optics monochromator and crystal analyzer. This is a team effort involving Susan Mini of the Physics Department at Northern Illinois University and Timothy Graber and P. James Viccaro, both scientists at The Consortium for Advanced Radiation Sources (CARS) of The University of Chicago. The spectrometer will allow utilization of full energy dispersion in scattering cross-section of atoms near the absorption edge. The instrumentation, which will be installed on beamline 15 at the Advanced Photon Source (APS), will be used primarily for valence-specific static and time-resolved chemical crystallography experiments. Applications include studies on large magnetoresistive oxides, surfaces and interfacial properties of soft materials and time-dependent studies of polymers. The AXD technique will help solve unknown crystal structures containing mixed-valent atoms in a way complementary to neutron diffraction and local probes such as x-ray absorption spectroscopy. AXD will also provide a useful method to study the behavior of an element in a single oxidation state with different types of coordination geometry. Currently, AXD studies are carried out with energy resolution of a few eV, which prevents selective modification of the structure factor of atoms of one particular valence over another. This instrument, with its significantly higher resolution, combined with the high spectral brilliance of the APS, will have significant impact in solid-state and materials science.
