Kirkendall Effect vs Corrosion of Silver Nanocrystals by Atomic Oxygen: From Solid Metal Silver to Nanoporous Silver Oxide

The corrosion of silver upon exposure to atomic oxygen is a unique effect reported in the 1980s and was highly studied to overcome the fast degradation of space shuttles in low earth orbit. In this work, we explored the conversion mechanisms of nanostructures from solid silver to nanoporous silver oxide upon exposure to radiofrequency air plasma. A broad panel of silver nanostructures with various shapes, sizes, and morphologies were considered to carefully examine the different stages of the oxidation process which evolve according to the considered model-system (e.g., nanosphere, nanowire, nanocube, or nanotriangle). Through a set of time-lapse studies and very specific experiments, we explained the generation of nanoporosity according to a mechanism based on two effects: (i) the high strain in the oxide shell generated as a consequence to the oxidation process and amplified by the bombardment of the material with the energetic species present in the radio frequency air plasma and (ii) the Kirkendall effect occurring at the Ag/Ag₂O interface as a consequence to the unbalanced diffusion rates of silver and oxygen ions through the oxide shell.