Superfast and Wafer-Scale Superlattice Film Engineering Enabled by an Ultralow-Interfacial-Energy Microenvironment.

The assembly of molecules or nanoparticles (NPs) into superlattice metamaterials endows them with remarkable optical, electrical, and magnetic properties, enabling applications in sensing, catalysis, and optical displays. However, traditional methods face challenges, such as complex procedures, long processing times, limited assembly areas, and poor reproducibility. The root cause of these challenges lies mainly in the complex and difficult-to-control interactions between assembly units such as ligands and NPs. In this study, a novel ultralow-interfacial-energy microenvironment between the water and oil phase is proposed for a rapid and large-scale superlattice assembly of NPs. The formation of the independently formed interfacial "third-phase" microenvironment hinges on two crucial factors. First, there is high immiscibility between densely packed perfluorodecanethiol ligands and a biphasic solvent system. Second, the coalescence events are accelerated at elevated temperatures. This microenvironment plays a dual role. Thermodynamically, it mitigates interparticle sintering and promotes the rapid establishment of supersaturation conditions that are conducive to the homogeneous nucleation of superlattices. Kinetically, it accelerates the coalescence process of "superlattice domains" through van der Waals interactions between neighboring NPs. This strategy reduces assembly time to under 80 min for forming superlattice monolayer films over areas up to 11 cm. Furthermore, the method is versatile, applicable to mono- and double-layer superlattices with subnanometer- to micrometer-scale materials. This work represents a breakthrough in traditional superlattice construction concepts. It offers new perspectives for ultrafast and large-scale superlattice assembly and broadens the application prospects of superlattice films of NPs in burgeoning fields such as biosensing and flexible displays.