SREL Reprint #2534

Applications of synchrotron-based X-ray microprobes

Paul M. Bersch and Douglas B. Hunter

Advanced Analytical Center for Environmental Sciences, Savannah River Ecology Laboratory,
The University of Georgia, Drawer E, Aiken, South Carolina 29802

Introduction: The past decade has witnessed significant advances in technologies related to X-ray spectroscopic techniques, both as a result of advances in X-ray optics, focusing devices, and detectors and because of greater availability of high-brilliance synchrotron facilities worldwide. The result is that synchrotron-based X-ray absorption fine structure spectroscopy (XAFS) has become a mainstream technique in a number of scientific disciplines and is providing molecular-level information not previously available using other techniques. The XAFS spectrum is typically separated into the X-ray absorption near-edge structure (XANES), also known as the near-edge extended X-ray absorption fine structure (NEXAFS) region, and the extended X-ray absorption fine structure (EXAFS) region. The XANES and NEXAFS spectrum is represented by the energy region just below to ~50 eV above the absorption edge and serves as a site-specific probe of local charge state, coordination, and magnetic moment of the central absorber. Above this energy, the extended fine structure, characteristic of an EXAFS spectrum, is manifested as oscillations in the absorption cross section arising from the constructive and destructive interference of the outgoing photoelectric wave and the incoming photoelectric wave backscattered from neighboring atoms. The EXAFS spectrum provides information on the number, identity, and distance (±0.02 Å) of neighboring atoms.  The ability to probe matter to determine the chemical state of a system at a high spatial resolution with high elemental sensitivity has been important to a number of fields, including the earth and environmental sciences, biosciences, colloid and surface science, and materials science, among others. The need for such data at high spatial resolution is a result of the heterogeneous nature of samples commonly examined in these disciplines and the importance of understanding how elemental and molecular distributions influence heterogeneous chemical reactivity or, conversely, how chemical reactivity influences heterogeneous elemental and molecular distributions. Traditional spectroscopic measurements of complex samples provide volume-averaged data that obscures important spatially variable chemical information. The ability to probe homogeneous or less heterogeneous domains within complex samples at high spatial resolution with minimal sample preparation provides an opportunity for more detailed molecular-level characterization. . . .

SREL Reprint #2534

Bertsch, P. B., and D. B. Hunter. 2001. Applications of synchrotron-based X-ray microprobes. Chemical Reviews 101:1809-1842.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).