Imaging, Understanding and Controlling of Nanoscale Materials Transformations

Seminar | November 12 | 4-5 p.m. | 120 Latimer Hall

 Haimei Zheng, Materials Sciences Division, Lawrence Berkeley National Lab

 College of Chemistry

Nanoscale materials often change structure and morphology during growth, self-assembly, and use as they interact with the environment, especially in solution processes. An understanding of their responses to an external stimulus at the atomic/molecular level may allow us to control their transformations, providing a rational pathway for the design of novel materials. For this purpose, we have developed in situ transmission electron microscopy (TEM) methods that allow real time imaging of material transformations with high spatial and temporal resolution under various external stimuli. We have focused on asymmetric nanostructures, such as one-dimensional (1D) nanowires, 2D nanosheets, and 3D-2D transitions. A variety of systems including metals, metal oxides, and transition metal dichalcogenides have been explored. Our direct observations and complementary theoretical studies have provided critical insights on the transformations of nanoscale materials. We then applied these insights to the design and synthesis of novel materials—including onion-like nanostructures made from a covalent organic framework (COF) and 2D “Van der Waals” nanostructures—that offer unique properties for technological applications.