Pt–Pd
nanoparticles are grown in the gas phase by a magnetron-sputtering
source and characterized by electron microscopy techniques for both
Pt-rich and Pd-rich compositions of the metallic vapor. It is shown
that this growth procedure can produce different types of core–shell
nanoparticles, in one step, with sizes in the range of 4–10
nm, according to the composition of the vapor being rich either in
Pt or in Pd. In all cases, the nanoparticles present intermixed cores
containing both Pt and Pd and shells made of the majority element,
i.e., of (PtPd)@Pt structure for the Pt-rich vapor and (PtPd)@Pd structure
for the Pd-rich vapor. Global searches of the optimal chemical ordering
show that none of these structures correspond to equilibrium configurations.
On the contrary, these core–shell structures are strongly out-of-equilibrium,
being the result of kinetic trapping phenomena. This is verified by
molecular dynamics growth simulations which are able to reproduce
both the different types of chemical ordering and the variety of geometric
shapes found in the experiments.