Applications of Synchrotron-Based X-ray Microprobes Paul M. Bertsch* and Douglas B. Hunter Advanced Analytical Center for Environmental Sciences, Savannah River Ecology Laboratory, The University of Georgia, Drawer E, Aiken, South Carolina 29802 Received September 20, 2000 Contents I. Introduction 1809 II. Experimental Configuration and Strategies for X-ray Microscopy, Micro-SXRF Imaging, Micro-XAFS, and Spectromicroscopy 1811 A. Colliminating X-rays for Microprobes and Microscopes 1812 B. X-ray Microscopy and Spectromicroscopy in the Soft X-ray Regime 1813 C. Hard X-ray Regime 1815 III. Applications of Synchrotron-Based Micro-SXRF, Micro-XAFS, and Spectromicroscopy 1817 A. Earth and Environmental Sciences 1817 1. Geochemistry and Cosmochemistry 1817 2. Soil and Environmental Sciences 1821 B. Biosciences 1830 C. Material and Polymer Sciences 1833 D. Miscellaneous Applications 1837 IV. Summary and Future Outlook 1837 V. Acknowledgments 1838 VI. References 1838 I. Introduction The past decade has witnessed significant advances in technologies related to X-ray spectroscopic tech- niques, 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 sepa- rated 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 or 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 constructive and destructive interference of the outgoing photo- electric wave and the incoming photoelectric wave * To whom correspondence should be addressed. Phone: (803) 725- 5637. Fax: (803) 725-3309. E-mail: bertsch@srel.edu. Paul M. Bertsch is a Professor of Soil Physical Chemistry and Mineralogy and Director of the Savannah River Ecology Laboratory of The University of Georgia. His research is focused on delineating the molecular form of contaminants (chemical speciation) in complex environmental samples and relating this to transportability and bioavailability. He is a participating research team member of the X-26A, microprobe beamline at the National Synchrotron Light Source, and a design team member of Sector 13, the Geo/Soil/Enviro CARS Collaborative Access Team, at the Advanced Photon Source. He served as Vice Chair of the Board of Governors of the Consortium for Advance Radiation Sources at the University of Chicago from 1994-1999. Douglas B. Hunter received a B.S. degree in Chemical Physics in 1985 from the University of Toronto and his M.S. and Ph.D. degrees in Botany from the Unversity of Vermont in 1987 and 1991, respectively. He worked at the Savannah River Ecology Laboratory of The University of Georgia developing new spectroscopic applications in the environmental sciences, where much of his time was devoted to developing applications of synchrotron-based X-ray techniques at the National Synchrotron Light Source and Advanced Photon Source. He is currently a Principal Scientist at the Savannah River Technology Center. 1809 Chem. Rev. 2001, 101, 1809-1842 10.1021/cr990070s CCC: $36.00 © 2001 American Chemical Society Published on Web 06/13/2001