Tip-Sonication-Induced Dilute Alloying of Metal Pairs with Limited Bulk-Immiscibility

Alloying metals with unfavorable bulk mixing thermodynamics remains challenging because conventional synthesis often favors elemental segregation rather than compositionally mixed nanoparticles. This study aimed to determine whether direct tip sonication can promote compositional intermixing in metal pairs with limited bulk miscibility and to distinguish sonication-specific effects from conventional thermal and chemical effects. Using Au-Mo as a model system, tip sonication of gold acetate and molybdenum hexacarbonyl in oleic acid successfully produced Au-Mo intermixed nanoparticles with an average diameter of 4.46 ± 0.89 nm and a bulk composition of 96.97 at% Au and 3.03 at% Mo. We also revealed that tip sonication alone was insufficient to induce alloy formation; rather, successful Au-Mo mixing required an appropriate precursor combination and solvent environment, highlighting the cooperative roles of physical energy input and reaction chemistry. The applicability of this strategy was further examined using other compositionally challenging metal pairs, including Ag-Rh and Au-Pt, for which tip sonication likewise produced bimetallic nanoparticles with spatially intermixed elemental distributions. Overall, these findings identify tip sonication as a simple nonequilibrium solution-phase route for accessing compositionally challenging dilute alloy nanoparticles.