Kayla Nguyen : Three-Dimensional Atomic Reconstruction using Electron Ptychography

Electrons play a pivotal role in stabilizing matter, but they are also tools that can reveal the underlying physics of complex systems from high energy physics to condensed matter. Electrons can be used as imaging probes, where properties of matter such as magnetism or topology can be observed atom-by-atom.  In this talk, I will show how electron ptychography, a computational phase retrieval technique, can improve resolution beyond the numerical aperture of electromagnetic lenses and reveal atomic structures in three-dimensions.  In particular, I use this ‘computation lens’ approach on Er: CeO₂ nanocrystals and thin films with dramatically different crystallographic orientations to uncover dopants, defects and strain with picometer precision.  Ptychography can also be extended to visualize topological magnetism in three dimensions.  Here, I will devise an approach to image magnetic structures of centrosymmetric skyrmions grown from amorphous FeGePt; here, internal Bloch domains with Néel caps can be reconstructed, as predicted from micromagnetic simulations. For non-idealized emergent materials, solving the atomic or magnetic structure in three dimensions can support results from density functional theory, micromagnetic simulations and enable a deeper understanding of a system’s physical properties.