The Kirkendall Effect in Binary Alloys: Trapping Gold in Copper Oxide Nanoshells

In this work, we report on the Kirkendall-induced hollowing process occurring upon thermal oxidation of gold-copper (Au-Cu) alloy nanowires and nanodots. Contrary to elemental metals, the oxidation reaction results in the formation of gold nanostructures trapped inside hollow copper oxide nanoshells. We particularly focus on the thermally activated reshaping mechanism of the gold phase forming the core. Using scanning transmission electron microscopy coupled to energy dispersive X-ray spectroscopy mapping, we show that such a reshaping is a consequence to the reorganization of gold at the atomic level. The gold nanostructures forming the core were found to be strongly dependent on the chemical composition of the alloy and the oxidation temperature. By selecting the appropriate annealing conditions (i.e., duration, temperature), one can easily synthesize various heteronanostructures: wire-in-tube, yolk-shell, oxide nanotubes embedding or decorated by Au nanospheres. The advanced understanding of the Kirkendall effect in binary alloy nanostructures that we have achieved in this work will open a new door for the fabrication and the design of novel multifunctional heteronanostructures for potential applications in different research fields including nano-optics/photonics, biomedicine, and catalysis.