Defect Self-Elimination in Nanocube Superlattices through the Interplay of Brownian, van der Waals, and Ligand-Based Forces and Torques

Understanding defect healing is necessary to predict the response of devices based on nanoparticle-superlattices with controlled electronic and optoelectronic performance. Key questions remain regarding the process of nanoparticle (NP) interactions and resulting assembly dynamics and defect self-elimination. In particular, for anisotropic particles, additional degrees of freedom beyond those of spherical particles, associated with rotational dynamics and torques, significantly impact phenomena. Here we investigate nanocube (NC) superlattices by employing liquid phase transmission electron microscopy, continuum theories, and molecular dynamics (MD) simulations. Analyzing interparticle forces and torques due to van der Waals, Brownian, and ligand interactions, we find that the latter dominates and the anisotropic NC morphology introduces significant torques. In inhomogeneous regions, unbalanced forces and torques induce NC translations and rotations that are transmitted to neighboring NCs, prompting “chain interactions” in a two-dimensional (2D) network, leading to defect self-elimination. The development of this fundamental understanding will further enable design and fabrication of defect-free superlattices, as well as those with tailored defects via assembly of anisotropic particles.