IMX Seminar Series - Visualizing the Bottom-up and Top-down Formation of Nanomaterials in Liquids with Transmission Electron Microscopy

Understanding nanoscale details of how materials form from a solution is fundamental for materials engineering and the fabrication of many functional devices. Nanomaterials either form via “bottom-up” processes, such as nucleation and growth, or “top-down” processes, such as nanoscale etching. Despite the technological importance of these processes, many of their details remain unknown. This is mainly due to a lack of proper experimental methods that enables the visualization of these solution-based processes at the nanoscale in real-time. 
Here, using time-resolved in situ liquid cell transmission electron microscopy (TEM), I will first describe the details of the nonclassical nucleation of crystals. Specifically, I will show nanocrystals nucleate from an aqueous solution via a three-step mechanism: 1) liquid-liquid phase separation of a solution gold solution into solute-rich and solute-poor regions, followed by 2) spontaneous formation of amorphous nanoclusters, which then 3) matures into crystalline nuclei that are large enough to sustain stable growth of nanoparticles.
Next, I will extend our approach to describe how templated semiconductor nanomaterials can be sculpted into desired nanostructures relevant for semiconductor microfabrication via wet etching by highlighting previously elusive steps involved in this reaction.
Our studies highlight the importance of direct visualization of nanoscale processes for the rational design of materials.


2) Refernces to 2 papers:
N. D. Loh, S. Sen, M. Bosman, S. F. Tan, J. Zhong, C. Nijhuis, P. Kral, P. Matsudaira, and U. Mirsaidov, "Multi-step Nucleation of Nanocrystals." Nature Chemistry 9, 77–82 (2017).

X. Liu, S.-W. Chee, S. Raj, M Sawczyk, P. Kral, U. Mirsaidov, “Three-Step Nucleation of Metal-Organic Framework Nanocrystals.” Proceedings of National Academy of Sciences U.S.A. 118(10), e2008880118 (2021).

Bio: Utkur Mirsaidov obtained his Ph.D. in Physics from the University of Texas at Austin, and after a 3-year postdoc at Beckman Institute at the University of Illinois at Urbana-Champaign, he moved to the National University of Singapore (NUS), first, as a research fellow, and then, as a faculty member. He is now an associate professor in the Department of Physics at NUS. Utkur’s lab uses in situ electron microscopy to study the nanoscopic details of phase transitions, nanomaterials synthesis, micro- and nanofabrication, and catalysis.