Imaging, Understanding, and Controlling Nanoscale Materials Transformations: Nano Seminar series

Prof. Haimei Zheng, LBNL, Materials Science Division
An understanding of nanoscale materials transformations is significant for the synthesis and applications of nanostructured materials. At the atomic level, heterogeneity and fluctuations may play a governing role in the transformation processes. The recent development of high-resolution liquid cell transmission electron microscopy (TEM) has enabled breakthroughs in our ability to follow the atomic level structural, morphological, or chemical changes of materials. Thus, it has provided an unprecedented opportunity to resolve the materials transformation mechanisms that may not be predicted based on thermodynamic equilibrium.
In this talk, I will present some recent work in my group on the development of liquid cell TEM for imaging, understanding, and further controlling of nanoscale materials transformations. First, surface ligand-controlled etching of palladium nanocrystals was observed using high resolution liquid cell TEM. We were able to track the etching of palladium nanocrystals at different facets. The adsorption of surface ligands (i.e., iron acetylacetonate and its derivatives) and their role as inhibitor molecules on the etching process were resolved.
Our observations further revealed that the etching was dominated by the interplay between palladium nanocrystal facets and surface ligands. Second, we discovered the defect-mediated ripening of Cd-CdCl2 core-shell nanoparticles (CSN). Ripening was found to start by dissolution of the nanoparticle with an incomplete CdCl2 shell, and that the Cd core that was exposed to the solution dissolved first. The growth of an adjacent Cd-CdCl2 CSN was achieved by generating crack defects in the shell, followed by ion diffusion through the cracks. The healing of crack defects led to a highly crystalline CSN at the end. The formation and annihilation of crack defects in the shell, accompanied by disordering and crystallization of the shell structure, mediate the ripening of CSN in the solution.
Lastly, I will also show our in situ liquid cell TEM study of H2 absorption/desorption in Pd nanocrystals.
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Haimei Zheng is a senior staff scientist at LBNL and an adjunct professor in MSE. She received the DOE Early Career Award in 2011, LBNL Director’s award for exceptional scientific achievements in 2013, MRS Medal in 2019, and MRS fellow in 2021.