Synchronized Monomer Kinetics Govern Ionic Nanorod Growth and Uncover Superlattice

Roxbyite (Cu₁.₈S) 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 Zn²⁺ 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.