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Equilibrium shape of core(Fe)–shell(Au) nanoparticles as a function of the metals volume ratio

Anne Ponchet 1 Segolene Combettes 1 Patrizio Benzo 1 Nathalie Tarrat 1 Marie-José Casanove 1 Magali Benoit 1
1 CEMES-SINanO - Surfaces, Interfaces et Nano-Objets
CEMES - Centre d'élaboration de matériaux et d'études structurales
Abstract : The equilibrium shape of nanoparticles is investigated to elucidate the various core–shell morphologies observed in a bimetallic system associating two immiscible metals, iron and gold, that crystallize in the bcc and fcc lattices, respectively. Fe–Au core–shell nanoparticles present a crystalline Fe core embedded in a polycrystalline Au shell, with core and shell morphologies both depending on the Au/Fe volume ratio. A model is proposed to calculate the energy of these nanoparticles as a function of the Fe volume, Au/Fe volume ratio, and the core and shell shape, using the density functional theory-computed energy densities of the metal surfaces and of the two possible Au/Fe interfaces. Three driving forces leading to equilibrium shapes were identified: the strong adhesion of Au on Fe, the minimization of the Au/Fe interface energy that promotes one of the two possible interface types, and the Au surface energy minimization that promotes a 2D–3D Stranski–Krastanov-like transition of the shell. For a low Au/Fe volume ratio, the wetting is the dominant driving force and leads to the same polyhedral shape for the core and the shell, with an octagonal section. For a large Au/Fe ratio, the surface and interface energy minimizations can act independently to form an almost cube-shaped Fe core surrounded by six Au pyramids. The experimental nanoparticle shapes are well reproduced by the model, for both low and large Au/Fe volume ratios.
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Submitted on : Saturday, August 8, 2020 - 4:07:35 PM
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Anne Ponchet, Segolene Combettes, Patrizio Benzo, Nathalie Tarrat, Marie-José Casanove, et al.. Equilibrium shape of core(Fe)–shell(Au) nanoparticles as a function of the metals volume ratio. Journal of Applied Physics, American Institute of Physics, 2020, 128 (5), pp.055307. ⟨10.1063/5.0014906⟩. ⟨hal-02913274⟩

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