Enhancing Symmetry Breaking Defects in Materials with a STEM Phase Plate

Local and extended defects are thermodynamically required in any physical system, and they disproportionally impact material properties. Because many important defects break long range order in materials, we aim to develop a high-resolution electron microscopy technique to amplify local crystal symmetry breaking signals.  Scanning transmission electron microscopy (STEM) is a natural tool to establish form-function relationships in these materials at the relevant length scales. The small probe size and versatile nature of STEM allows multimodal signals to be leveraged for advanced characterization. For example, researchers have demonstrated how a 4D-STEM approach can leverage information encoded in reciprocal space to investigate a material's symmetry.[1] The incorporation of a phase plate in the probe forming aperture of a STEM can efficiently enhance signals from a wide range of spatial frequencies.[2] In this study, we optimize the geometry of STEM phase plates given the local symmetry of crystalline structures, with the goal of more easily observing defects. We will present STEM simulations and calculations that demonstrates this effect in a variety of systems.

[1] M. Krajnak and J. Etheridge. PNAS. 117(45), 27805-27810 (2020).

[2] C. Ophus et al. Nat. Commun. 7, 10719 (2016).