Abstract
The oxidation of Fe@Au core@shell clusters with sizes below 5 nm is studied via high resolution scanning transmission electron microscopy. The bimetallic nanoparticles are grown in superfluid helium droplets under fully inert conditions, avoiding any effect of solvents or template structures, and deposited on amorphous carbon. Oxidation resistivity is tested by exposure to oxygen at ambient conditions. The passivating effect of Au-shells is studied in detail and a critical Au shell thickness is determined which keeps the Fe core completely unharmed. Additionally, we present the first synthesis of Fe@Au@Fe-oxide onion-type structures.
Highlights
Core@shell nanoparticles represent a class of materials with unique physical properties and various ne-tuning possibilities via an adjustment with respect to size, morphology and composition
The latter type could be synthesized by exposure to oxygen during particle synthesis
Fe clusters which are exposed to oxygen a er synthesis show characteristic cavities,[16] a result of Kirkendall dynamics, an effect observed for several metals:[17] metal atoms inside the cluster are dragged towards the surface where oxidation takes place
Summary
Core@shell nanoparticles represent a class of materials with unique physical properties and various ne-tuning possibilities via an adjustment with respect to size, morphology and composition. Fe clusters which are exposed to oxygen a er synthesis show characteristic cavities,[16] a result of Kirkendall dynamics, an effect observed for several metals:[17] metal atoms inside the cluster are dragged towards the surface where oxidation takes place. In this context, a passivation with a layer of gold seems reasonable in order to retain a highly magnetic core. We determine a critical minimum thickness of the gold shell necessary to protect the iron core and give an explanation of our ndings based on density functional theory
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