# Defect Migration in Supercrystalline Nanocomposites

## TL;DR

This paper explores how defects form and move in supercrystalline nanocomposites, revealing insights into their structural evolution and mechanical properties.

## Contribution

The study reveals how processing steps influence defect migration and healing in supercrystalline nanocomposites using advanced imaging and simulations.

## Key findings

- Pressing SCNCs into pellets causes distortion of the fcc superlattice.
- Emulsion-templated assembly creates supraparticles with stacking faults and size-dependent symmetries.
- Heat treatment heals stacking faults and causes grain boundary migration via disconnection motion.

## Abstract

Supercrystalline nanocomposites (SCNCs) are nanostructured
hybrid
materials with a variety of unique functional properties. Given their
periodically arranged building blocks, they also offer interesting
parallels with crystalline materials. They can be processed in multiple
forms and at different scales, and cross-linking their organic ligands
via heat treatment leads to a boost of their mechanical properties.
This study shows, via X-ray and in situ scanning transmission electron
microscopy (STEM) analyses, how each of these processing steps plays
a distinct role in the generation, migration, interaction, and healing
of supercrystalline defects. Pressing of SCNCs into bulk pellets leads
to a distortion of the otherwise fcc superlattice,
while emulsion-templated self-assembly yields supraparticles (SPs)
with stacking faults and size-dependent symmetries. Heat treatment
at the same temperatures as those applied for the organic cross-linking
has significant effects on planar defects. Stacking faults migrate
and get healed, as also confirmed via molecular dynamics simulations,
and intersupercrystalline “grain” boundaries migrate
via anisotropic motion of disconnections. These rearrangements of
defects at the supercrystalline scale (tens of nanometers) in nanocomposites
with high mechanical properties (compressive strength of 100–500
MPa) provide insights into the formation and evolution of ordered
assemblies of functionalized nanoparticles.