Advanced STEM Techniques : NBED Strain Mapping and HRSTEM Multislice Simulations

Abstract

Dr. Rohini Sankaran will present her previous research on advanced STEM techniques specifically discussing:

• 4D-STEM-based nanobeam electron diffraction (NBED) strain mapping of nanoindented Ti-Based Gum Metal, and
• Multislice simulations of embedded omega precipitates in Nb-lean Ti-based Gum Metals

4D-STEM is a relatively newer microscopy technique in which diffraction patterns are obtained simultaneously with the HAADF signal at each probe position. Very large data sets are typically created from this method, thus extensive post-acquisition data analysis is required. Specifically, the presentation will provide details on the experimental setup and data analysis necessary for generation of rotation and strain maps from data acquired via 4D-STEM-based NBED experiments. Interpretation of strain maps from deformed Gum Metals will be discussed. [Acta Materialia 151 (2018) 334-346]. The second topic describes implementation of the “multislice” method to generate HRSTEM image simulations. Such simulations can be critical for proper interpretation of contrast exhibited in complex, atomic resolution HAADF images. As an example, HAADF simulations of omega precipitates in beta-Ti alloys reveal that the origin of “trilayer” periodicity in HRSTEM images is not due to elemental ordering, but rather due to the fact that the precipitates are embedded within the matrix. [Philosophical Magazine 94 (2014) 2900-2912].

About the Speaker

Dr. Rohini Sankaran received her B.S. in Materials Science and Engineering with a minor in Mathematics from Stanford University in 2008. She went on to receive M.S. (2012) and Ph.D. (2015) in Materials Science and Engineering under Prof. J. W. Morris, Jr. and Prof. Andy Minor at University California at Berkeley studying the plastic deformation mechanisms of Ti-based Gum Metals. During this time, she was an affiliate at the National Center for Electron Microscopy (NCEM), Molecular Foundry at Lawrence Berkeley National Labs (LBNL) where she performed in-situand ex-situ TEM nanomechanical testing, atomic resolution STEM imaging, multislice simulations, and NBED strain mapping in order to resolve secondary phases and defect structures in Gum Metals. Her work has resulted in multiple peer-reviewed publications and presentations in professional conferences.