Effects of the Core Location on the Structural Stability of Ni-Au Core-Shell Nanoparticles

7 pags., 6 figs.-- ACS Liveslides presentation: https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.9b05765Structural changes of Ni-Au core shell nanoparticles with increasing temperature are studied at atomic resolution. The bimetallic clusters, synthesized in superfluid helium droplets, show a centralized Ni core, which is an intrinsic feature of the growth process inside helium. After deposition on SiNx, the nanoparticles undergo a programmed temperature treatment in vacuum combined with an in situ transmission electron microscopy study of structural changes. We observe not only full alloying far below the actual melting temperature, but also a significantly higher stability of core-shell structures with decentralized Ni cores. Explanations are provided by large-scale molecular dynamics simulations on model structures consisting of up to 3000 metal atoms. Two entirely different diffusion processes can be identified for both types of core-shell structures, strikingly illustrating how localized, atomic features can still dictate the overall behavior of a nanometer-sized particle.This research has been supported by the Austrian Science Fund (FWF) under grant P 29893-N36 and FWF PIR8-N34, the Spanish Agencia Estatal de Investigacion (AEI) and the Fondo Europeo de Desarrollo ́ Regional (FEDER, UE) under grant no. MAT2016-75354-P, and by the COST Action CM1405 “Molecules in Motion” (MOLIM). The authors would like to acknowledge the use of HPC resources provided by the ZID of Graz University of Technology and by the Vienna Scientific Cluster (VSC). The CESGA super-computer center (Spain) is also acknowledged for having provided computational resources. Further support by NAWI Graz is gratefully acknowledged