Designing Guidelines for Bragg Coherent Nano Diffraction in Crystalline Thin Films

Recent constructions and upgrades of fourth-generation light sources have dramatically improved the feasibility of Bragg coherent nano diffraction experiments. However, obtaining physical information from these experiments is dramatically different from measurements in the transmission geometry and often poses challenges for some of the established methods such as ptychography. Here, we focus on the Bragg nano diffraction of thin film materials in the reflection geometry and demonstrate how quantitative insights about the lattice deformation are encoded in nano diffraction patterns through the thickness fringes. This insight comes from forward simulation and enables a maximum-likelihood approach for extracting lattice strain and tilts from the experimental data. The use and limitations of this approach are discussed using nano diffraction patterns from exemplary materials. At the end of the paper, we put forward a guideline for performing Bragg coherent nano diffraction measurements, from the choice of X-ray parameters to the data acquisition and analysis methods. Our work addresses a major bottleneck in utilizing coherent X-rays for thin film research and provides an actionable roadmap, especially for new users of coherent nano diffraction.