In situ atom-resolved tracing of element diffusion in NiAu nanospindles.

The structure evolution behaviors of NiAu nanospindles in oxidizing/vacuum conditions were studied by in situ scanning transmission electron microscopy. The spindle structure transforms into Ni@Au@NiO multi-shell structure in the oxidizing atmosphere following an oxidation-driving multilayer reconstruction mechanism. In the vacuum condition, the NiAu nanospindles evolve along four distinct stages: (i) polyhedron recrystallization of Ni matrix; (ii) facets-selected segregation and recrystallization of Au component; (iii) single crystallization of Ni matrix; (iv) wrapping diffusion of Au component. The investigation here provides a practical insight into the structural stability of NiAu bimetallic catalysts through a thermal processes.