Investigating materials under extreme pressure using diamond anvil cells (DACs) requires very small samples. X-ray diffraction studies of such samples therefore require beams focused to <5 μm. Fortuitously, advances in light-source and beamline design mean that modern synchrotrons, such as PETRA III and ESRF-EBS, now deliver sub-μm focusing. Combined with increased source brightness, fast motors, user-friendly control interfaces, and data processing advances, 2D mapping of microscopic samples becomes routine, with exposures on mid-Z samples reduced to seconds. We demonstrate the use of sub-μm beams, with high-resolution 2D scans, to map pressure and strain gradients. We show how small scans are applied to collect optimum data, and how the sample can affect the pressure inferred from the pressure calibrant. Although sub-μm beams can improve compressibility data, they may also introduce undersampling, revealing variability on μm length scales. We provide recommendations for the use of sub-μm beams for extreme conditions research.
Lonsdale et al. (Thu,) studied this question.