Miaofang Chi: Visualizing Energy Materials at the Atomic Scale

Miaofang Chi has joined the faculty of the Department of Mechanical Engineering and Materials Science in Duke University’s Pratt School of Engineering. Her appointment, which is joint with a continuing appointment at Oak Ridge National Laboratory, began on June 1, 2023. A leading expert in scanning transmission electron microscopy (STEM), Chi will focus her efforts on studying energy and quantum materials at the atomic level by advancing and applying cryogenic STEM.

Chi earned her PhD in materials science and engineering from the University of California, Davis. Over the past 15 years, she has spent time as a researcher at several national laboratories, including Lawrence Livermore National Laboratory and, most recently, Oak Ridge National Laboratory, where she won the Director’s Award for Outstanding Individual Accomplishment in Science and Technology in 2015 and 2021.

STEM scans a focused electron probe about half of an angstrom in diameter—roughly the same as a single atom of hydrogen—at the object being studied. By analyzing the exiting electrons after they interact with the object, the object can be mapped atom-by-atom.

While extremely powerful, the technology has several challenges, including often damaging the object being imaged. This limits the types of objects and materials that can be imaged using STEM, often excluding delicate systems like biological tissue and other soft materials, such as polymers used in fuel cells and batteries. One way around this drawback is to image the samples at cryogenic temperatures, making the structures more resilient to the electron beam.

“Maintaining cryogenic temperatures while keeping samples immobile enough to see single atoms is still very challenging. I’m developing strategies to overcome those technical difficulties.”

Miaofang Chi

“Many materials used in energy conversion and storage systems, such as polymers and fast ion conductors, are sensitive to electron beams, so cryo-STEM is the only way to image them on an atomic scale,” Chi said. “But maintaining cryogenic temperatures while keeping samples immobile enough to see single atoms is still very challenging. I’m developing strategies to overcome those technical difficulties.”

Atomic Scale Cryogenic STEM can be improved in three fundamental ways: hardware, signal acquisition and data analysis. Fast scanning and shutter speeds can help minimize the effects of slight vibrations and movements. A better understanding of how electrons interact with materials within these systems can lead to more sensitive detection methods. Machine learning can help interpret smaller amounts of data, allowing researchers to use less damaging electron beams.

Chi is working on all three aspects of improving and applying the technology. Her efforts are already revealing the atomic-scale origins of performance degradation in battery interfaces.

“During my campus visit, I was filled with excitement. The vibrant research culture and the campus’s atmosphere resonated with me, and I was genuinely inspired by the faculty and students’ passion for this field of work.”

Miaofang Chi

Batteries convert chemical energy into electrical energy. During discharge, electrons are released from the anode and flow through the external circuit, while positively charged ions move through the electrolyte to the cathode, creating an electric current. Recharging the battery reverses this process, restoring electrons at the anode and replenishing energy. However, if electrons directly traverse the electrolyte, it can lead to battery failure and safety hazards. Understanding atomic charge and ion transport mechanisms is vital for designing safer and more powerful batteries.

Another aspect of Chi’s work is focused on studying the atomic structures and workings of quantum materials. “Quantum phenomena don’t appear within materials like superconductors until they’re cooled to extremely low temperatures, which often requires liquid hydrogen,” Chi said. “Cryo-STEM provides unique information on these materials while they are at relevant temperatures.”

At Duke, Chi will continue her research in these areas. The university has invested in a state-of-the-art cryo-STEM, set to be installed in the Shared Materials Instrumentation Facility in 2024. Her expertise with this system is expected to foster collaborations across various interdisciplinary research topics, including energy materials, which new colleagues David Mitzi and Olivier Delaire are working on, microelectronics, which Natalia Litchinitser is focusing on, and even biological research.

“I’ve been extremely impressed by the unwavering commitment I’ve witnessed at Duke, particularly from the engineering school, toward energy materials research,” Chi said. “During my campus visit, I was filled with excitement. The vibrant research culture and the campus’s atmosphere resonated with me, and I was genuinely inspired by the faculty and students’ passion for this field of work.”