Nanocrystals often change structure and morphology during formation and applications. Liquid phase transmission electron microscopy (TEM) allowing to trace the dynamic processes at the atomic or nanometer scale opens the opportunity to resolve the transformation mechanisms.<br/><br/>In this talk, I will first show our recent study on the reversible large deformation of individual PbSe nanocrystals during superlattice transitions. We made unique carbon film liquid cells for this study. Direct observation revealed that PbSe nanocrystals change shape when interacting with the neighboring particles and the deformation was dependent on the chemistry during ligands exchange. For instance, when oleate ligands were removed from nanoparticle surface with ethylene glycol (EG), negligible changes of individual nanocrystals were observed. When a small amount of ethylenediamine (EDA) was added (EDA:EG=1:1000), large shape changes (up to 40%) were found. Molecular Dynamics simulation suggests that the electrostatic dipolar interactions between nanocrystals played a major role in the observed reversible shape changes. The deformation of individual PbSe nanocrystals introduces defects in the final superlattice, thus negatively impact the solar cell device performance. Other work that will be presented in this talk includes our study of 2D nanostructure formation with 3D nanoparticles as intermediates and nanoparticle coalesce with a focus on the role of defects in the nanoscale structural evolution.

In situ liquid phase electron microscopy imaging of nanocrystal transformations

ACS Spring Meeting 2021

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