(253al) Sintering of Bimetallic Ag-Au Nanoparticles By Molecular Dynamics

Nanoparticles have attracted strong interest due to their novel properties and have been explored widely in photonics, electronics, catalysis, sensors, information storage, photography, imaging and biological labeling. For example, gold nanoparticles are used extensively in catalysis and silver nanoparticles have remarkable antibacterial properties. However, the former exhibit reduced electron transfer on Au(111) surface, hindering the adsorption of O₂ on such surfaces, while the latter are highly cytotoxic prohibiting their use in biomedical applications. Bimetallic nanoparticles (e.g. Ag-Au) often exhibit enhanced chemical, catalytic and plasmonic properties compared to their corresponding parent materials and, thus, can enhance the affinity with O₂compared to pure gold nano-catalysts or decrease the cytotoxicity of silver (Sotiriou et al., 2014).

Physical properties (e.g. reactivity and ligand adsorption) of such nanostructures depend on the particles crystal structure and surface facet orientation. Experimental investigation of particlesâ?? nanocrystallinity with electron microscopy leads to incomplete characterization as it is based on the analysis of 2D projections of nanoparticles. However, Molecular Dynamics (MD) simulations can be used to provide physical insight in crystal structure changes and dynamics with atomistic detail (Buesser and Pratsinis, 2015) and can complement the above experiments, especially for very small nanoparticles.

Here, MD simulations are used to systematically investigate the sintering mechanism and crystallinity dynamics of Ag-Au nanoparticles of various sizes and temperatures. The sintering rate of coalescing Ag-Au nanoparticles of various initial morphologies (segregated, core-shell or alloys) is investigated for different particle sizes and temperatures. The characteristic sintering time of Ag-Au nanoparticles (determined by tracking the evolution of the surface area during sintering or coalescence) can be bracketed in-between those of pure Ag and Au nanoparticles.

Furthermore, particle crystallinity depends on the synthesis process conditions (Goudeli and Pratsinis, 2016) and lead to the exposure of different facets affecting surface chemistry and product particle morphology and their catalytic properties (e.g. catalytic activity and selectivity). The atoms at the grain or particle boundaries are disordered compared to the bulk atoms, especially during particle adhesion. Such defects (e.g. grain boundaries) at the atomic scale can strongly affect electrical, optical and mechanical properties of 2D materials.

Keywords:sintering rate, bimetallic silver-gold, molecular dynamics.

References

Buesser, B., and Pratsinis, S.E. (2015) J. Phys. Chem. C, 119, 10116-10122.

Goudeli, E., Eggersdorfer, M.L., and Pratsinis, S.E. (2015) Langmuir, 31, 1320-1327.

Goudeli, E., and Pratsinis, S.E. (2016) AIChE J, 62, 589-598.

Sotiriou G A, Etterlin G D, Spyrogianni A, Krumeich F, Leroux J-C, and Pratsinis S E. (2014). Chem. Commun. 50: 13559-13562.