Alloying processes in nanometre-size Ag@Au and Au@Ag core@shell particles are studied via high resolution Transmission Electron Microscopy (TEM) imaging.
Structural 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 SiN
x
, 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.
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