NSLS-II Seminar

Surface and interface phenomena play a profound role in low-temperature geochemistry and environmental chemistry. Mineral weathering and growth, sorption reactions, and surface-mediated (or catalyzed) transformations have a major impact on the composition and speciation of aquatic and atmospheric systems. A broad array of competing reactions influence such processes and the reaction prevalence is often a sensitive function of the physicochemical and biological variables within the system.

The GSECARS surface and interface program provides a unique facility to study environmental surface and interface phenomena. Established techniques include: crystal truncation rod diffraction; resonant anomalous scattering; grazing angle reflectivity; grazing-incidence x-ray absorption spectroscopy; long-period x-ray standing wave fluorescence-yield measurements; grazing-angle x-ray powder diffraction; and total reflection x-ray fluorescence. In order to fully characterize complex environmental interfaces, detailed analyses from complementary probes within a controlled sample environment are required. Using the general purpose diffractometer at the GSECARS undulator beamline 13-IDC all of these techniques can be utilized in a single experimental run.

I will present results from recent experiments focusing on the fundamental aspects of interface structure and structure-reactivity relationships, followed by studies of more complex phenomena such as mineral dissolution and growth. Finally I will discuss new technical developments that enhance the array of surface and interface tools.