Understanding the Formation of Conductive Mesocrystalline Superlattices with Cubic PbS Nanocrystals at the Liquid/Air Interface

We
report the formation of conductive mesocrystalline superstructures
of cubic PbS nanocrystals (NCs) through directional cross-linking
with organic semiconductors at the liquid/air interface monitored
simultaneously by in situ grazing incidence small angle X-ray scattering
and grazing incidence X-ray diffraction. We determine the superlattice
type, its symmetry and parameters, and the atomic orientation of NCs
from the time-resolved scattering patterns. The superlattice contraction
follows an exponential decay during ligand exchange, preserving always
the two-dimensional square geometry. We attribute the contraction
to the continuous replacement of oleic acid with smaller cobalt/copper
4,4′,4″,4‴-tetraaminophthalocyanine molecules.
In these superlattices, the NCs are directed with a [100]AL axis perpendicular to the liquid surface for the whole assembly
period. The kinetics and structural results provide a direct correlation
between the superstructure and their atomic orientation on the liquid
surface during self-assembly followed by ligand exchange.