Bragg Coherent Modulation Imaging: Strain- and Defect- Sensitive Single Views of Extended Samples

Abstract: Nanoscale heterogeneity (including size, shape, strain, and defects) significantly impacts material properties and how they function. Bragg coherent x-ray imaging methods have emerged as a powerful tool to investigate, in three-dimensional detail, the local material response to external stimuli in reactive environments, thereby enabling explorations of the structure-defect-function relationship at the nanoscale. Although progress has been made in understanding this relationship, coherent imaging of extended samples is relatively slow (typically requiring many minutes) due to the experimental constraints required to solve the phase problem. Here, we develop Bragg coherent modulation imaging (BCMI), which uses a modulator to solve the phase problem thereby enabling fast, local imaging of an extended sample. Because a known modulator is essential to the technique, we first demonstrate experimentally that an unknown modulator structure can be recovered by using the exit wave diversity that exists in a standard Bragg coherent diffraction imaging (BCDI) experiment. We then show with simulations that a known modulator constraint is sufficient to solve the phase problem and enable a single view of an extended sample that is sensitive to defects and dislocations. Our results pave the way for BCMI investigations of strain and defect dynamics in complex extended crystals with temporal resolution limited by the exposure time of a single diffraction pattern.