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

Abstract

The gas-phase growth of AuAg and PtPd clusters up to sizes $\sim$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.

Machine Learning Assisted Clustering of Nanoparticle Structures

“…Typically, the optimal structure (and also the chemical ordering if there are two or more metals) of an NP is searched by global optimizations techniques, such as basin hopping (BH) or genetic algorithm, which implement clever ideas to explore the atomistic potential energy landscape. Then, thanks to Molecular Dynamics (MD) simulations, the thermal evolution and/or growth of an NP composed of thousands of atoms can be followed for tens of μs . Even larger sizes and time scales are achieved by coarse-grained models, in which also complex environments of nanoparticles (for example, solid substrates and embedding matrices) can be simulated and studied …”

“…Then, thanks to Molecular Dynamics (MD) simulations, the thermal evolution and/or growth of an NP composed of thousands of atoms can be followed for tens of μs. 7 Even larger sizes and time scales are achieved by coarse-grained models, in which also complex environments of nanoparticles (for example, solid substrates and embedding matrices) can be simulated and studied. 8 A common feature of these simulations is the production of large outputs, usually many NP structures in some threedimensional coordinates file format.…”

Interplay between interdiffusion and shape transformations in nanoalloys evolving from core–shell to intermixed structures

“…39 Form and parameters of the potential are available in Ref. 40,41 for AgAu and PtPd and in Ref. 42 for AuCu.…”

Growth pathways of exotic Cu@Au core@shell structures: the key role of misfit strain

“…the minority Cu atoms are located in the core while the outer shell is exclusively formed by Au atoms. The distribution of minority Cu atoms within the nanoparticles has been characterized by calculating their gyration radius with respect to their geometric centre during the kinetic growth process 29 . The results are shown in Figure S1 in the ESI.…”

“…Depending on the growth temperature (see Table 1), Type I simulations starting from a truncated octahedral seed produce different structures such as tetrahedra, irregular double twins and icosahedra. Here we focus on the growth pathway to the double twin structures, while the transitions to tetrahedra and icosahedra, which have been already discussed elsewhere 26,29 , are shown in the ESI (Figure S7).…”