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MSE Colloquium: Dr. Marc De Graef, Advances towards quantitative Lorentz Transmission Electron Microscopy

All dates for this event occur in the past.

2040 Fontana Labs
140 W 19th Ave
Columbus, OH 43210
United States

Abstract
The study of magnetic domain walls in conventional magnetic materials as well as more complex topologically protected magnetic excitations (e.g., skyrmions and hopfions) requires a special technique known as Lorentz Transmission Electron Microscopy or LTEM.  In this seminar we will begin with an in-depth review of the basics of Lorentz image formation, including the computation of the Aharonov-Bohm phase shift which is the main quantity of interest. Then we will introduce the Foucault and Fresnel imaging modes as well as Differential Phase Contrast approach; we will show that Fresnel imaging is really just an application of conventional high resolution TEM phase contrast imaging. We will introduce the Transport-of-Intensity Equation (TIE) based on the Lorentz contrast transfer function and illustrate how this equation can be solved for the electron wave phase shift. We will conclude the presentation with a number of application of LTEM to different materials systems, including the reconstruction by tomographic methods of the 3-D magnetic vector potential.

Bio
Marc De Graef received his B.S. and M.S. degrees in Physics from the University of Antwerp (Belgium) in 1983, and his Ph.D. in physics from the Catholic University of Leuven (Belgium) in 1989, with a thesis on copper-based shape memory alloys. He then spent three and a half years as a postdoctoral researcher in the Materials Department at the University of California at Santa Barbara before joining Carnegie Mellon University in 1993 as an assistant professor. He is currently a professor in the Department of Materials Science and Engineering and director of the J. Earle and Mary Roberts Materials Characterization Laboratory. In 2023, he was appointed as the John and Claire Bertucci Distinguished Professor of Engineering.

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