Applied Physics and Materials Science Special Seminar

Abstract:

Scanning transmission electron microscopy (STEM) is a powerful tool for direct characterization of nano- to atomic-scale features in materials. However, for electron beam-sensitive and weakly scattering structures, STEM is not so simple. The dose efficiency and image contrast in conventional imaging modes can be quite limiting for beam-sensitive or low atomic number structures. Many of these challenges can be ameliorated with a 4D-STEM approach, where a diffraction pattern is acquired at each position in real space. The structural information in this data can be reconstructed to efficiently characterize atomic ordering and measure properties of materials not possible with conventional imaging modes.

In this talk, I will present our phase retrieval 4D-STEM experimental and computational methods. While the phase of the electron wave is lost upon measurement, I will show how it can be reconstructed in several ways, including differential phase contrast, parallax, and iterative electron ptychography. I will discuss how we can use physics-informed constraints to show new insights in 2D and 3D for structures across biological and materials sciences. I will highlight the broad applicability of these methods through examples ranging from solving protein structures, to characterizing atomic-scale defects in 2D-materials, to measuring strain in 3D in core-shell heterostructures. I will also demonstrate how our implementation of these methods in the open-source toolkit py4DSTEM has allowed researchers around the world to access these methods. Finally, I will present my design for an electrostatic phase plate for electron beam control and demonstrate how it can improve the transfer of information in phase retrieval experiments.

More about the Speaker:

Stephanie Ribet is a postdoctoral researcher at the National Center for Electron Microscopy, which is part of the Molecular Foundry at Lawrence Berkeley National Laboratory. She received her PhD from the Department of Materials Science and Engineering at Northwestern University.

At Northwestern, she worked on characterizing soft matter and hybrid materials at multiple length scales with microscopy and spectroscopy techniques. As a postdoc, she focuses on experimental and computational development of high-resolution STEM techniques for characterization of beam-sensitive materials. She is a recipient of the MRS Gold Graduate Student Award and the Department of Energy Office of Science Graduate Student Research Fellowship. Stephanie is co-founder and co-chair of the annual Women in Microscopy conference.