@article{12535,
  author = {Yuan Lo and Jihan Zhou and Arjun Rana and Drew Morrill and Christian Gentry and Bjoern Enders and Young-Sang Yu and Chang-Yu Sun and David Shapiro and Roger Falcone and Henry Kapteyn and Margaret Murnane and Pupa Gilbert and Jianwei Miao},
  title = {X-ray linear dichroic ptychography},
  abstract = {Ptychography, a powerful scanning coherent diffractive imaging method, has attracted considerable attention for its general applicability. Here, we demonstrate X-ray linear dichroic ptychography to study the crystal orientations of the calcium carbonate in coral samples. In contrast to the absorption contrast commonly observed in linear dichroic imaging, dichroic ptychography at pre-oxygen K-edge shows significant and unique dichroic phase contrast, which has not been reported. The dichroic ptychography images reveal the presence of both narrow and wide c-axis angular spread in the submicrometer coral fragments, which are confirmed by 4D STEM. We expect X-ray linear dichroic ptychography to be a high-resolution, dose-efficient tool to broadly study optically anisotropic materials such as tooth enamel, bone, seashells, brittlestars, and polymers.Biominerals such as seashells, coral skeletons, bone, and tooth enamel are optically anisotropic crystalline materials with unique nanoscale and microscale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Using Seriatopora aculeata coral skeleton as a model, here, we experimentally demonstrate X-ray linear dichroic ptychography and map the c-axis orientations of the aragonite (CaCO3) crystals. Linear dichroic phase imaging at the oxygen K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (\<35\textdegree) and wide (\>35\textdegree) c-axis angular spread in the coral samples. These X-ray ptychography results are corroborated by four-dimensional (4D) scanning transmission electron microscopy (STEM) on the same samples. Evidence of co-oriented, but disconnected, corallite subdomains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. We expect that the combination of X-ray linear dichroic ptychography and 4D STEM could be an important multimodal tool to study nano-crystallites, interfaces, nucleation, and mineral growth of optically anisotropic materials at multiple length scales.X-ray linear dichroic ptychography data presented in this work are available for download at the Coherent X-Ray Imaging Data Bank (https://www.cxidb.org/id-109.html), and electron tomography data presented in this work are available for download at Mendeley Data (https://data.mendeley.com/datasets/f62bfbndym/1). All data needed to evaluate the conclusions in the paper are present in the paper and/or SI Appendix.},
  year = {2021},
  journal = {Proceedings of the National Academy of Sciences},
  volume = {118},
  number = {3},
  pages = {e2019068118},
  month = {2021-01},
  publisher = {National Academy of Sciences},
  issn = {0027-8424},
  url = {https://www.pnas.org/content/118/3/e2019068118},
  doi = {10.1073/pnas.2019068118},
}