Growth of size-matched nanoalloys – a comparison of AuAg and PtPd

Abstract

The gas-phase growth of AuAg and PtPd clusters up to sizes ~3 nm is simulated by Molecular Dynamics. Both systems are characterized by a very small size mismatch and by a tendency of the less cohesive element to segregate at the nanoparticle surface. The aim of this work is to figure out the differences in the behavior between these two bimetallic systems at the atomic level. For each system, three simulation types are performed, in which either one species or both species are deposited on preformed bimetallic seeds. Our results show that core@shell and intermixed chemical ordering arrangements can be obtained, in agreement with the available experimental data. In the case of core@shell arrangement, the purity of the surface layer is perfect for Ag-rich and Pd-rich nanoparticles, whereas in Au-rich and Pt-rich ones, some tendency to surface migration of minority atoms (Ag or Pd) is observed. This tendency is somewhat stronger for Ag than for Pd. The analysis of the internal arrangement of the nanoparticles indicates that in the growth process the mobility of Pd and Ag minority atoms is stronger than that of Au and Pt minority atoms.