  X-ray nanodiffraction is applied to study the formation and correlation of
domain boundaries in mesocrystalline superlattices of PbS nanocrystals with
face-centered cubic structure. Each domain of the superlattice can be described
with one of two mesocrystalline polymorphs with different orientational order.
Close to a grain boundary, the lattice constant decreases and the superlattice
undergoes an out-of-plane rotation, while the orientation of the nanocrystals
with respect to the superlattice remains unchanged. These findings are
explained with the release of stress on the expense of specific
nanocrystal-substrate interactions. The fact that correlations between adjacent
nanocrystals are found to survive the structural changes at most grain
boundaries implies that the key to nanocrystal superlattices with macroscopic
domain sizes are strengthened interactions with the substrate.
