Abstract

The typical example of XAFS is a transition metal in a homogeneous model system, but we often need to apply XAFS in more complex and difficult systems, particularly heterogeneous natural materials. Such materials include environmental, geologic or extraterrestrial samples. This talk will cover some applications of XAFS — both XANES and EXAFS — when samples are heterogeneous, complex mixtures, or involve lighter elements like sulfur or phosphorus. In those challenging situations, XAFS can still be a powerful tool, through creative approaches to data collection, analysis and interpretation. Components in heterogeneous mixtures can be probed using microbeam XAS, with careful consideration of experimental design. Even microbeam measurements may still result in data that is a complicated mixture of several components, requiring careful and systematic data-processing efforts to untangle and quantify the contributions of each component. Tender-energy (~1 to 5 keV) XAFS provides access to lighter elements including P, S and Ca, as well as L or M edges of heavier elements such as Zr and U. Challenges of these measurements range from critical experimental considerations (e.g. particle size, sampling depth, harmonics) through data processing.