X-ray analysis of minerals is routinely used to provide detailed information on crystal structures, but has not been applied to the imaging of mineral surfaces due to limitations in resolution. Recently, a team of scientists at Argonne National Laboratory developed a new X-ray method that utilizes interfacial phase contrasts resulting from a focused X-ray beam reflecting off either side of a stepped cleavage surface. X-ray reflection interface microscopy (XRIM) uses a monochromatic X-ray beam that is focused using a condenser Fresnel zone plate onto a small (~1 mm) crystalline sample. The resulting reflected X-ray beam is then projected onto an area detector using another objective Fresnel zone plate. Interfacial phase contrast is generated by destructive interferences resulting from X-rays reflecting off of a stepped crystallographic surface. This technique can resolve a 0.6 nm high monomolecular step in a crystal surface, and generates images that depict the spatial distribution of monomolecular steps on the cleaved surface.

Surface topography on an orthoclase (001) surface imaged at incident angle of 2.7^◦, using a photon energy of 10 keV, with the scattering plane intersecting the image along the vertical axis.

This novel approach represents a more than 10-fold increase in X-ray image resolution. This new method will permit direct observation of interfacial reactions such as dissolution and crystal growth under extreme chemical conditions, which would not be possible with atomic force microscopy because of probe tip reactivity problems. This method could also be used to study the nucleation and growth of crystalline nanoparticles, as well as to characterize the interfacial surface structure of fine-grained minerals such as clays and zeolites. 

For additional details, see:

Fenter, P., Park, C., Zhang, Z., and Wang, S., 2006, Observation of subnanometre-high surface topography with X-ray reflection phase-contrast microscopy. Nature Physics, 2 (10), 700-704, doi:10.1038/nphys419.