  The unique topology and physics of chiral superlattices make their
self-assembly from nanoparticles a holy grail for (meta)materials. Here we show
that tetrahedral gold nanoparticles can spontaneously transform from a
perovskite-like low-density phase with corner-to-corner connections into
pinwheel assemblies with corner-to-edge connections and denser packing. While
the corner-sharing assemblies are achiral, pinwheel superlattices become
strongly mirror-asymmetric on solid substrates as demonstrated by chirality
measures. Liquid-phase transmission electron microscopy and computational
models show that van der Waals and electrostatic interactions between
nanoparticles control thermodynamic equilibrium. Variable corner-to-edge
connections among tetrahedra enable fine-tuning of chirality. The domains of
the bilayer superlattices display strong chiroptical activity identified by
photon-induced near-field electron microscopy and finite-difference time-domain
simulations. The simplicity and versatility of the substrate-supported chiral
superlattices facilitate manufacturing of metastructured coatings with unusual
optical, mechanical and electronic characteristics.
