SEMINAR

DEPARTMENT OF MECHANICAL ENGINEERING

Phase Transformations of Nanoscale Systems Using In Situ TEM

Prof. Judy J. Cha
Dept. of Mechanical Engineering and Materials Science, Yale University

Abstract

Many nanoscale systems exhibit phase transformations in response to stimuli, which subsequently change the material properties of the systems, providing opportunities to create functional devices. Here, we use in situ transmission electron microscopy (TEM) as a tool to study how phase transformations occur, deviate, and are controlled at the nanoscale under either thermal or electrical stimuli. I will discuss two examples of phase transformation: IBM’s confined phase change memory (PCM) cells with a surfactant layer, which showed a record endurance of 2x1012 programming cycles, and metallic glass nanostructures that are used to test the limits of classical nucleation theories. In the PCM example, we demonstrate a surprising self-healing property, enabled by the symmetric design of the device [1]. With the nanoscale metallic glasses, we observe that crystallization can be greatly affected by the nanocscale confinement and the underlying local structure of the glass [2]. In both examples, atomic scale in situ TEM investigations uniquely reveal detailed and unexpected phenomena, guiding us to build better models and theories for nanoscale phase transformations. I will also discuss phase transformations of two-dimensional transition metal dichalcogenides induced by electrochemical intercalation of Li+ and their energy applications [3], as well as a one-dimensional topological superconductor [4].

[1] Adv. Mater. 30, 1705587 (2018); [2] Nat. Comm. 6:8157 (2015); Nat. Comm. 8:1980 (2017); Nat. Comm. 10:915 (2019);[3] Adv. Mater. 30, 1706076 (2018); Small 15, 1900078 (2019);[4] APL Materials 5, 076110 (2017); arXiv:1907.04199 (2019).

Biography

Judy J. Cha is the Carol & Douglas Melamed Associate Professor in the Department of Mechanical Engineering and Materials Science at Yale University. Prior to Yale, she was a post-doctoral researcher at Stanford University in the Department of Materials Science and Engineering. She received her Ph.D. in Applied Physics from Cornell University in 2009. Notable awards she received include the NSF CAREER (2018), the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholar for quantum materials (2017), the Yale Arthur Greer Memorial Prize (2016), the IBM Faculty Award (2014), the Presidential Student Award from Microscopy Society of America (2010), and the Graduate Student Silver Award at the Spring Materials Research Society meeting (2008). Her research focuses on synthesis and transport measurements of topological nanomaterials and two-dimensional transition metal dichalcogenides in nanostructures; in situ TEM studies of phase transformations of nanomaterials; and potential applications of these materials in quantum computing and energy.