Abstract Colin Ophus is an Associate Professor in the Materials Science and Engineering Department and a Center Fellow at the Precourt Institute at Stanford University. He was formerly a Staff Scientist at the National Center for Electron Microscopy (NCEM), part of the Molecular Foundry user facility, at Lawrence Berkeley Lab. His research focuses on experimental methods, reconstruction algorithms, and software codes for simulation, analysis, and instrument design of scanning transmission electron microscopy (STEM). In 2018 he received a DOE Early Career award, and in 2022 he was awarded the Burton medal from the Microscopy Society of America (MSA). He has published over 200 articles and given invited talks around the world. He is project leader for the open-source Prismatic STEM simulation and py4DSTEM analysis codes, and editor-in-chief for the newly launched interactive journal Elemental Microscopy.43Scanning transmission electron microscopy (STEM) has become an essential tool for materials science research, where it has been applied to atomic-scale imaging, diffraction, spectroscopy, and 3D tomography of many materials. The most popular STEM method is annular dark field (ADF) imaging, which provides approximately linear and incoherent contrast. This makes 2D imaging simple and interpretable, and the 3D tomographic reconstructions using ADF straightforward to implement. Atomic electron tomography (AET) of nanostructures performed using ADF STEM can both resolve the 3D positions of every atom and estimate the species of each atomic site. However, ADF-STEM is relatively dose-inefficient, and cannot be used to image beam sensitive materials or resolve light elements such as carbon or oxygen. These limitations prevent AET from being applied to materials such as polymers, lithium-containing battery materials, and biological samples. To move beyond these limits, we require more sensitive and dose-efficient methods such as phase contrast imaging. High speed direct electron detectors now allow us to record a full 2D image of the diffracted STEM probe over a 2D grid of probe positions, producing a four-dimensional (4D)-STEM dataset. In this talk, I will demonstrate several phase contrast 4D-STEM methods, including center-of-mass differential phase contrast (CoM-DPC), parallax (or tilt-corrected bright field) imaging, and iterative ptychography, applied to inorganic and biological materials at high resolution. I will also show how we have applied ptychographic atomic electron tomography (PAET) to solve the 3D structure of a hybrid material composed of a complex ZrTe nanowire encapsulated in a double-walled carbon nanotube. I will emphasize the important role of developing open-source algorithms, codes, and simulation methods to promote robustness, reusability, and repeatability for scientific studies.Associate Professor, Materials Science and Engineering, Stanford University, USACenter Fellow, Precourt Institute, Stanford University, USANew Dimensions in Phase ContrastScanning Transmission Electron MicroscopyColin Ophus Invited Talk: S4-2
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