Chiral Assemblies of Pinwheel Superlattices on Substrates

TL;DR

This study demonstrates the spontaneous formation of chiral pinwheel superlattices from tetrahedral gold nanoparticles on substrates, revealing their controllable chirality and potential for advanced metastructured coatings.

Contribution

It introduces a new self-assembly pathway for chiral superlattices with tunable chirality and strong optical activity, advancing the design of functional metastructures.

Findings

Tetrahedral gold nanoparticles form dense, chiral pinwheel superlattices on substrates.

Chirality can be tuned by adjusting nanoparticle connections.

Superlattices exhibit strong chiroptical activity.

Abstract

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.