In Situ Electron Microscopy: Revealing Unseen Materials Dynamics in Liquids or Gases
Dr. Haimei Zheng
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley CA
Understanding how materials grow and transform in their working environments is essential to the development of functional materials and devices that are important to energy applications. We study a wide range of physical and chemical processes of materials in liquids or gases by in situ transmission electron microscopy. These include nucleation, growth and structural transformation dynamics of nanoparticles during chemical reactions. In the first part of my talk, I will present our recent work on growth dynamics of colloidal nanoparticles in liquids with the focus of shape control mechanisms and surfactant effects. During growth, nanoparticles frequently changes in shape enabled by the ease of mass transport across the nanoparticle. Understanding the structural flexibility of nanoparticles during chemical reactions is critical since it strongly affects their functions, such as in heterogeneous catalysis. In the second part of the talk, I will show an example of direct observation of atomic phase segregation of a bimetallic PtCo nanocatalyst. Combining the in situ observations with modeling studies, we have also identified the driving force for the phase segregation. These studies are important for the design of novel catalysts with the improved catalytic reactivity and stability. Finally, I will present our recent development of electrochemical liquid cells for in situ study of electrochemical processes of materials for energy storage applications.
Dr. Zheng received her Ph.D in Materials Science and Engineering from University of Maryland, College Park in Dec. 2004. She moved to UC Berkeley in early 2004 with his advisor, Prof. Ramesh, and continued working in Ramesh group until 2006. She was a postdoc of Prof. Paul Alivisatos in the Department of Chemistry at UC Berkeley jointly at National Center for Electron Microscopy (NCEM) of LBNL. She became a staff Scientist of LBNL in 2010. She was a winner of DOE Office of Science Early Career Award in 2011.