INTERFACIAL X-RAY SCATTERING FROM SMALL CRYSTALS

Fine-grained metal oxides and clay minerals are among the most reactive phases in soils, inspiring decades of research into their structures and chemical interactions with natural waters. Experiments have generally relied upon averaging over many particles in bulk powders or slurries. Crystal truncation rod (CTR) X-ray diffraction provides atomic-scale insights into the structures of single crystal surfaces and their interfaces with gases and liquids, but has historically been limited to phases that grow to a few millimeters in size. Recent developments at the GeoSoilEnviroCARS X-ray beamlines at the Advanced Photon Source have enabled the measurement of CTR data from crystals as small as 100 microns in lateral dimensions. Measurements have now been made from basal surfaces of the birnessite-group Mn-oxide chalcophanite and the kaolin group clay mineral dickite. These studies arise directly from collaborations with Drs. Jeffrey Post and David Bish, and would not have been possible without their insights as well as the decades of groundwork they have laid in understanding the structures of these important classes of minerals.