Valence-Free Open Nanoparticle Superlattices

A cornerstone of next-generation 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 exceptionally rare simple cubic phase, with tunable lattice constants. Theoretical models and simulations elucidate the underlying interactions, unlocking novel avenues for engineering valence-free nanoparticle superlattices.