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Nanomaterials with core-shell architectures are prominent examples of strain-engineered materials. The lattice mismatch between the core and shell materials can cause strong interface strain, which affects the surface structures. Therefore, surface functional properties such as catalytic activities can be designed by fine-tuning the misfit strain at the interface. To precisely control the core-shell effect, it is essential to understand how the surface and interface strains are related at the atomic scale. Here, we elucidate the surface-interface strain relations by determining the full 3D atomic structure of Pd@Pt core-shell nanoparticles at the single-atom level via atomic electron tomography. Full 3D displacement fields and strain profiles of core-shell nanoparticles were obtained, which revealed a direct correlation between the surface and interface strain. The strain distributions show a strong shape-dependent anisotropy, whose nature was further corroborated by molecular statics simulations. From the observed surface strains, the surface oxygen reduction reaction activities were predicted. These findings give a deep understanding of structure-property relationships in strain-engineerable core-shell systems, which can lead to direct control over the resulting catalytic properties.

No abstract

By creating epitaxy between two different materials, the misfit strain at the interface can be finely controlled [1,2]. Core-shell architectures are prominent examples of such strain-engineered materials, where material properties can be designed by fine-tuning the misfit strain at the interface [3]. To fully utilize the interfacial strain effect, it is essential to have an atomic-scale understanding of their 3D interface structures. Here, we elucidate the full 3D atomic structure of Pd@Pt core-shell nanoparticles at the single-atom level via atomic electron tomography [4]. Full 3D displacement and strain maps of coreshell nanoparticles are obtained, which revealed a direct correlation between the surface and interface strains. It also shows clear Poisson effects at the scale of the full nanoparticle as well as the local atomic bonds. The strain distributions show a strong shape-dependent anisotropy, which is further corroborated by molecular statics simulations. From the observed surface strains, the surface oxygen reduction reaction activities were predicted [5]. These findings can give a deep understanding of structure-property relationships in core-shell systems, and suggest that the strain, as well as catalytic properties at the surface, can indeed be finely controlled through proper core-shell engineering.