CFN Colloquium

While traditional imaging methods like scanning transmission electron microscopy (STEM) offer local insights into nanoscale features, challenges arise in resolving the three-dimensional (3D) relationships between atomic, chemical, and polar structure. To overcome many of these challenges and recover information from the projection, multislice electron ptychography has emerged as a powerful tool in which the 3D sample information is iteratively reconstructed from 4D STEM datasets. In this talk, I will first discuss a methodological framework for determining acquisition parameters for robust multislice ptychographic reconstructions. From these insights, we will explore 3D chemical and short-range structural order at anti-phase boundaries (APBs) in a paraelectric material on the verge of becoming AFE at room temperature. The ptychographic reconstruction enables the disambiguation of various structural and chemical boundary models, concluding that the boundary is inclined and disordered compared to the 'bulk' thin film. Second, AFE nanodomains are found to reside within the chemically disordered regions of the APB. The results highlight the impact of nanoscale heterogeneities on phase stability, providing insights for engineering antiferroelectric materials through chemistry and defect control. Overall, multislice electron ptychography emerges as a transformative tool for unraveling the nanoscale intricacies of polar domain structures in various functional materials. Beyond oxides, I will demonstrate that ptychographic reconstructions can directly quantify single defects and defect complexes as color centers in SiC. This is achieved on a slice-by-slice basis, imparting direct, 3D information. This will be explored using simulated ptychographic datasets encompassing an array of defects in various positional configurations. Finally, we will discuss the limitations of capturing three-dimensional structures and the ability to capture small displacements arising from substitution and the formation of v-TM complexes. Biographical: James earned his B.S. in Materials Science & Engineering from Rensselaer Polytechnic Institute in 2006 and his Ph.D. from the University of California Santa Barbara in 2010. After his graduate work, he joined the Department of Materials Science and Engineering faculty at North Carolina State University in January 2011. In 2019, he moved his group to MIT's Department of Materials Science & Engineering. His research focuses on applying and developing (scanning) transmission electron microscopy techniques to quantify materials' atomic structure and chemistry to inform our understanding of relaxor/ferroelectric, mechanical, optical, and quantum properties. For his research, he has been honored with numerous awards, including the Presidential Early Career Award for Scientists and Engineers (PECASE), the NSF CAREER award, an AFOSR Young Investigator grant, the Microanalysis Society K.F.J Heinrich award, and the Microscopy Society of America Burton Medal.