Abstract
Topological structures in ferroic materials can emerge as particle-like objects such as skyrmions
and merons, with real-space swirling arrangements of the order parameter that not only have
mathematical beauty but hold promise for potential applications in next generation nanodevices.
As those ferroic textures are intrinsically nm-scale and dynamic, developing methods for
visualizing and characterizing their detailed 3D structure is a critical step in understanding their
properties and exploring possible phase transitions. I will show how the measurement of
structural information such as polarization, strain, chirality, electric or magnetic fields was made
possible by new imaging methods, i.e., four-dimensional scanning transmission electron
microscopy (4D-STEM) diffraction imaging. I will report the observation of room temperature
Néel-type skyrmion in a van der Waals ferromagnet accompanied by a change in crystallographic
symmetry and chemical order. Second, I report the emergence of achiral polar meron lattice
(topological charge of +1/2) from disordered but chiral skyrmion (topological charge of +1) phase
transition driven by elastic boundary conditions. Further, using multislice electron ptychography,
the 3D structural distortions of unknown polar textures in complex oxide heterostructures can
be resolved at unprecedented resolution and precision.
Speaker Bio
Yu-Tsun Shao studies quantum materials by novel electron microscopy techniques, specifically
4D-STEM. He studies the (multi-)ferroic crystals with the aim to elucidate the microscopic origin
of interactions among local polar/magnetic order, strain, and chiralities during topological phase
transitions. Before joining USC, Yu-Tsun did postdoctoral work in Professor David Muller’s group
at Cornell University and received his Ph.D. in Materials Science and Engineering at the University
of Illinois at Urbana-Champaign in 2018, under the mentorship of Professor Jian-Min Zuo.
Abstract
Bioresource materials such as cellulose, chitin, and lignin, are usually low-cost, biocompatible, and abundant in nature. The synthesis of functional materials from these bioresource materials can address long-term challenges in Food-water-Energy Nexus, such as resource and energy depletion, food security, water scarcity, and climate change. However, the adaption of chemical functionalization and self-assembling methodologies to renewable resource materials for functional materials is very challenging due to their macromolecular structures, heterogeneous properties, poor solubility, and the disturbance of impurities. In this talk, we will summarize how we explore self-assembly methods to produce new nanostructures and endure new functions for renewable resource materials. Several examples will be discussed. For example, glycerol, a biowaste from the biodiesel process, has been assembled into a nano-core-shell structure for a smart food packaging film sensor for universal real-time food spoilage monitoring. Biomass waste or cellulose can be assembled as multiple-function controlled-release fertilizers and smart membranes. Ultimately, we would like to use these self-assembly nanostructures from renewable resources to achieve a high-efficiency circular bioeconomy.
Speaker Bio
Dr. Tong has been an Associate Professor and James C. Barber Faculty Fellow in the School of Chemical and Biomolecular Engineering at Georgia Tech since January 2022. She is also the initiative leader in waste valorization in the food-water-energy nexus of the Renewable Bioproduct Institute (RBI). Previously, she served as an assistant and associate professor since 2010 at the University of Florida. She earned her Ph.D. in chemical engineering from Georgia Tech in 2007, followed by work at Ch2M Hill until 2009. Tong’s research focuses on synthesizing functional sustainable materials and catalytical conversion for biochemicals and biofuels from renewable resources. She has published 73 journal papers and 4 patents. Her research has been supported by NSF, USDA, NAS, and DOE. She secured about $5 million in grants after joining Georgia Tech in 2022. Dr. Tong has also served as an associate editor for three journals and held leadership roles in AIChE.