Atomic Observation of Initial Oxidation of Metal: From Oscillating Incubation to Catastrophic Depletion

Oxidation-induced material failure severely threatens the service life of metallic materials spanning from industrial engineering components to nanoscale catalysts. In particular, the sudden structural collapse during early oxidation is highly destructive, however, its underlying atomic-scale mechanisms remain elusive. Herein, we directly captured the real-time dynamic evolution of this degradation using in situ atomic-resolution transmission electron microscopy. The structural degradation proceeds through an initial reversible oscillation followed by a rapid collapse. During the oscillatory stage, the reversible detachment and recapture of the outermost Ag atoms create transient surface vacancies that facilitate the incorporation of oxygen into the subsurface. Localized lattice expansion induced by subsurface oxygen lowers the lateral diffusion barrier, shifting the transport mechanism from vertical penetration to lateral diffusion. Ultimately, subsurface oxygen accumulation weakens interfacial metallic bonds, precipitating abrupt surface exfoliation. This study proposes the atomic-scale mechanism of how oxygen infiltrates the metal subsurface to trigger catastrophic failure, demonstrating a direct relationship between atomic-scale strain and macroscopic structural degradation during metal oxidation.