Operando Electrochemistry at Dynamic Catalyst Interfaces
Electrocatalysts lie at the interface between materials science and electrochemistry and represents one of the most promising approaches for enabling renewable energy technologies to mitigate carbon emissions through the use of hydrogen fuel cells and the electrochemical reduction of CO2. One of the key challenges is understanding how to achieve and sustain electrocatalytic activity under operating conditions for extended time periods, and such fundamental understanding calls for the use of time-resolved nanoscale operando analytical methods. In this presentation, I will introduce our recent progress on developing operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM), which simultaneously enables quantitative electrochemistry on microelectrodes and quantitative STEM based imaging, diffraction and spectroscopy. Operando electrochemical 4D-STEM in liquid, driven by machine learning, has shown great potential to interrogate complex structures of active sites of energy materials at solid-liquid interfaces. In particular, I will present my latest work on multimodal operando studies of combining EC-STEM and correlative synchrotron based X-ray methods to elucidate the longstanding enigmatic nature of Cu active sites as Cu nanograins for selective CO2 electroreduction.
Yao Yang will be an assistant professor of chemistry at Cornell University starting in Fall 2024. He received a B.S. at Wuhan University in 2015 and Ph.D. at Cornell University in 2021. He was co-advised by Profs. Héctor Abruña in electrochemistry and David Muller in electron microscopy, and worked extensively with Prof. Francis DiSalvo on solid-state materials. As a Miller fellow at UC Berkeley, he works with Prof. Peidong Yang on developing operando STEM for investigating the dynamic evolution of nanocatalysts for CO2 conversion to liquid fuels.
SiGe/Si Heterojunction Drain Transistor for Faster 3D NAND Flash Memory Erase
Some 3D NAND flash memory technologies utilize the phenomenon of Gate Induced Drain Leakage (GIDL) for erase operation. As the number of memory cells stacked in a 3D NAND string increases, larger GIDL current is needed to maintain the same erase speed. In this work, the use of silicon-germanium (SiGe), which has a smaller band-gap energy compared to silicon (Si), is proposed to augment GIDL current through enhanced band-to-band tunneling. TCAD simulation confirms that, when the heavily doped drain and a portion of the undoped channel region of the drain transistor comprise SiGe, both GIDL current and erase speed are enhanced significantly, while maintaining the same off-state current in inhibit mode operation.
Dasom received her B.S. in material science from Sungkyunkwan University and M.S. in material science from KAIST. After obtaining the M.S degree, Dasom worked as a TCAD simulation engineer in SK Hynix for several years. Currently, she is a second-year PhD student in EECS working with professor Tsu-Jae King Liu. Her research interests focus on semiconductor devices for logic and memory applications, including exploring innovative pathways to enhance the performance and characteristics of semiconductor devices through a combination of TCAD simulation, measurement and experiment.