Material Structures Form via Particle Assembly

Particle assembly has been recognized as a common pathway for forming material structures, such as superlattices. Understanding particle interactions is necessary to control material structures and the corresponding properties, e.g. electronic and optoelectronic performance of devices based on nanoparticle-superlattices. However, a key challenge remains to understand nanoparticle interactions: defect self-elimination during the assembly processes, especially with anisotropic NPs which cause rotational dynamics and torques. We investigate the role of ligands and electrolytes in solution during nanoparticle assembly and defect self-elimination processes by integrating liquid phase transmission electron microscopy, continuum theories, and molecular dynamics simulations. We find that electrolytes and ligands can determine the particle separation depending on the conditions. Ligand interactions can dominate over the forces from Brownian motions and van der Waals interactions. Unbalanced forces and torques induce defect self-elimination. The mechanistic understanding will further enable the design and fabrication of defect-free superlattices and those with tailored defects via the assembly of anisotropic particles.