Monday, May 11, 2026
4:00 pm – 5:00 pm
Presenter: Dr. Steffi Woo, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
Abstract:
Two-dimensional semiconductors, such as transition metal dichalcogenides (TMDs), and their van der Waals heterostructures, provide a versatile platform to study correlated phases and other emergent phenomena. Twist angle and lattice mismatch in such heterostructure systems offer tunable knobs to engineer periodic moiré potentials that reshape the electronic and excitonic landscape. However, the direct correlation of structural variations to the local excitonic behavior is often challenging because conventional optical methods are diffraction-limited and cannot resolve the relevant lengthscales. An ideal technique is cryogenic aberration-corrected scanning transmission electron microscopy (STEM) capable of resolving the sub-nanometer scale periodicities combined with 5–10 meV energy resolution for measuring the excitonic resonances using monochromated electron energy-loss spectroscopy (EELS) [1]. In this talk, I will discuss some of our key insights, practical strategies, and remaining challenges in correlating the local excitonic response of TMDs to nanoscale structural or dielectric inhomogeneities utilizing the multimodal capabilities of electron spectromicroscopy.
[1] Woo SY and Tizei LHG. 2D Mater. (2025) 12, 012001.
Bio:
Dr. Steffi Woo is a R&D Associate in the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory. She has a B.Eng. in Materials Engineering and Society with a minor in Chemistry from McMaster University (Canada). She obtained her M.A.Sc. in Materials Engineering for her thesis work on the characterization of extended defects in group III-V semiconductor thin films by conventional TEM also at McMaster University in the group of Prof. Gianluigi Botton. Her Ph.D. work focused on the structural and chemical variations in group III-nitride nanowire heterostructures, also supervised by Prof. Botton. She was previously a post-doctoral researcher in the STEM group at the Laboratoire de Physique des Solides in Orsay (France) with a focus on the optical response of 2D materials, including h-BN and transition metal dichalcogenides using electron energy-loss spectroscopy (EELS) and cathodoluminescence. Her current research interest centers on the interplay on structure and optical response in 2D materials and related heterostructures.