Spatiotemporally Revealing the Formation of Metal–Metal Compound Superatoms and Their Self-Assembly via Programmed Chilling Microfluidics: The Case of Au–WO₃ Superatoms

Formation of nanoaggregates or nanocomposites via constructive self-assembly of single atoms and/or subnano clusters has been of great interest for atom-resolved synthesis, particularly for the defined construction of superatoms and their assemblies with defined microstructures and physicochemical properties, by which their atom numbers, geometries, and electronic states can be precisely regulated. Here, a programmed chilling microfluidic process with high spatiotemporally resolved kinetics was developed, which could precisely control the kinetic/thermodynamic parameters of the superatoms formation process (e.g., flow rate, temperature, and retention time in the microchannels), leading to precise regulation of sizes and heterogeneous structures of superatoms. Metal–metal compound superatoms (1–14 Å in size) and their self-assembled aggregates were successfully synthesized using Au–WO3 as a model system. An abundance of heterogeneous microstructures could be observed in their free suspension cases. A simple formation model was further developed to simulate the microstructures of Au–WO3 superatoms based on the formation energy of Au clusters (3–55 atoms) and WO3 molecular clusters via density functional theory. Results indicated that ultratiny Au superatoms were stabilized during nucleation via WO3 molecular cluster passivation and stabilizer protection within the programmed chilling microfluidic system. This stabilization mechanism was critical for achieving precise microstructure control in free superatoms, demonstrating scale-out potential.