Materials Science Research Lecture

***Refreshments at 3:45pm in Noyes lobby

Abstract:

Driven by electron ptychography, a revolution in electron microscopy is again underway. First, because the aberrations of the electron optics can be accounted for after the acquisition, the technique enables imaging resolution constrained only by the atomic thermal vibrations. Moreover, the intricate structural details in three dimensions can be recovered by applying multislice methods. Combined, these capabilities unlock previously inaccessible information about material structure and behavior. While these recent advances are proving essential to the atomic scale characterization of materials, however, the meticulous selection of intertwined acquisition and computational parameters is required and can be ambiguous.

In this talk, I will present a methodological framework to determine acquisition parameters for robust ptychographic reconstructions. I will introduce two metrics, namely, areal oversampling and Ronchigram magnification, grounded in physical principles to elucidate the selection criteria for these multislice ptychography parameters. Through extensive simulations, we comprehensively assess the reliability of these two metrics across diverse conditions. Our findings unequivocally demonstrate their efficacy in guiding successful reconstruction processes. Moreover, we corroborate these insights by validating them against experimental ptychographic data, revealing a striking alignment between trends observed in simulated and real-world experiments.

Applying this approach, I demonstrate how the technique can be used to investigate the polar order (and disorder) of functional oxides in 3D. The resulting picometer-precise-measurements will be shown to enable the capability to directly observe chemically induced static atomic displacements within complex oxide solid solutions, enabling an understanding of how polarization changes throughout the thickness the thin TEM sample. Finally, I will highlight our results of studying point and extended defects in SiC for quantum computing applications.

More about the Speaker:

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.