Valence-free open nanoparticle superlattices

TL;DR

This paper introduces a versatile method for assembling open, cubic nanoparticle superlattices without the need for directional interactions, using oppositely charged polymers to control electrostatic assembly.

Contribution

It presents a novel, unified strategy for creating valence-free nanoparticle superstructures with tunable symmetries and lattice constants, expanding beyond traditional valence-based assembly methods.

Findings

Successfully assembled various cubic superlattices including diamond and zinc-blende.

Controlled electrostatic interactions enable tunable lattice parameters.

Theoretical models explain the assembly mechanisms.

Abstract

A cornerstone of advanced materials design is establishing a framework for assembling nanoparticle superstructures with tailored symmetries. A longstanding challenge has been assembling diamond-like superstructures for photonic devices. Traditionally, such open superstructures require functionalized nanoparticles with directional or anisotropic interactions, reminiscent of valence bonding in a diamond. Here, we present a robust strategy for assembling valence-free nanoparticles into a broad array of cubic superstructures. By grafting nanoparticles with oppositely charged, end-functionalized water-soluble polymers of adjustable molecular weight, we gain control over electrostatic interactions and conformational constraints. This unified approach yields lattices analogous to rock salt, CsCl, zinc-blende, diamond, and the rare simple cubic phase, with tunable lattice constants. Theoretical models and simulations elucidate the underlying interactions, providing a framework for engineering valence-free nanoparticle superlattices.