Synchronized Monomer Kinetics Govern Ionic Nanorod Growth and Uncover Superlattice

Abstract Roxbyite (Cu ₁ . ₈ S) nanorods are promising building blocks for nanoscale device architectures, but a limited understanding of their growth has long hindered structural control, preventing the discovery of advanced arrangements such as superlattices. This study follows a chain of observations that led to three transformative insights. First, an adventitious impurity is identified, synthesized, and purified that promotes unprecedented anisotropic growth. Second, mechanistic findings are rationalized by a novel kinetic model introducing two proposed concepts: Decomposition‐Rate Synchronization and Nucleation Selectivity. Third, partial Zn ² ⁺ exchange of the long nanorods uncovers superlattice heterostructures—architectures inaccessible with short rods. These insights redefine ionic nanocrystal growth mechanisms beyond cadmium chalcogenides and open new pathways for programmable, monodisperse heterostructure synthesis.