Direct solution synthesis of intermetallic AuCu and AuCu₃ nanocrystals and nanowire networks

A modified polyol process has been used to synthesize intermetallic nanocrystals and nanowire networks directly in solution using a one-pot reaction. The synthesis of AuCu nanocrystals in tetraethylene glycol shows that atomically ordered intermetallic nanocrystals form above 250 °C, while atomically disordered alloy nanocrystals form at lower temperatures. The particle size increases with increasing solvent temperature, and there is a gradual shift from spherical to ellipsoidal morphology. Fully ordered intermetallic AuCu nanocrystals synthesized at 310 °C have an average particle width and height of 10 ± 3 and 8 ± 2 nm, respectively, and exist with faceted ellipsoidal, hexagonal, and cubic shapes. Replacing tetraethylene glycol with ethylene glycol, diethylene glycol, triethylene glycol, and glycerol yields highly branched nanowire networks. The morphology of the nanowire networks remains the same for all of the solvents, but the structure can be tuned from fully disordered alloy to fully ordered intermetallic AuCu, based on the boiling point of the solvent. The nanowire networks synthesized in ethylene glycol show that they likely form through a nanoparticle coalescence mechanism. By changing the stoichiometry of Au and Cu in solution, intermetallic AuCu₃ nanocrystals and nanowire networks can also be synthesized using tetraethylene glycol and glycerol, respectively. These results establish that it is possible to simultaneously control the structure, size, shape, and composition of intermetallic nanocrystals using solution chemistry, which has important implications for both fundamental scientific studies and future technological applications.