Seminar Date: Monday, May 11, 2026
Time: 1:00 PM PT
Location: 67-3111 & Zoom
Talk Title: Nanoscale Excitonic Response in Two-Dimensional Semiconductors with Electron Spectromicroscopy
Zoom link
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.
