Phase Stability, Melting, and Alloy Formation of Au-Ag Bimetallic Nanoparticles

The molecular dynamic method has been used to simulate the phase stability, melting, and alloy formation of bimetallic Au-Ag nanoparticles (NPs) with cuboctahedral, decahedral, icosahedral, and spherical shapes. The alloy NPs have more negative formation energy than the core/shell NPs, indicating the former is more stable than the latter. During melting, both core/shell and alloy NPs start to melt from the surface and then the core. The melting temperature of cuboctaheral, icosahedral, and decahedral NPs is similar, indicating the small influence of shape on melting temperature. During the alloying process, the alloy formation ability follows cuboctaheral > icosahedral > decahedral NPs, revealing the significant effect of particle shape on alloying formation. Only the surface was found to become alloy whereas the core remains pure components after annealing. It is shown that the UV-vis method alone is not enough to characterize the alloy formation in the entire NP, but only in the surface shell.