IMAGING INTERFACIAL REACTIONS WITH X-RAY REFLECTION INTERFACE MICROSCOPY

A fundamental understanding of aqueous-mineral interface reactivity is essential for developing robust predictive models that describe elemental mobility and transport in the near-surface environment. X-ray reflection interface microscopy (XRIM), a capability established recently at the Advanced Photon Source, is a powerful new tool for interfacial studies. XRIM probes interfaces through the reflection of a focused x-ray microbeam, and therefore has all of the sensitivities of x-ray reflectivity (XR) including interfacial structure and composition. The use of an x-ray objective lens enables the lateral variation of the x-ray reflectivity signal to be spatially resolved, thereby yielding images of lateral topography and structure with direct sensitivity to sub-nm vertical features (e.g., unit-cell height steps). The first results on the application of XRIM to probing interfacial reactivity will be described, in which we observe dissolution of the orthoclase (001) surface at alkaline pH. Specifically, ex-situ XRIM images, combined with in-situ time-resolved XR measurements reveal changes in the dissolution rate and dissolution process due to the addition of NaCl. Recent results on the extending this capability to imaging in-situ processes will be described, including both the challenges and the unique opportunities.

*This work is supported by the US Dept. of Energy, Office of Basic Energy Sciences, Geoscience Research Program.