Coupled outward and inward oxide growth during metal oxidation.

In copper oxidation, in situ environmental TEM shows Cu2O grows simultaneously at the O2/Cu2O surface interface and the buried Cu2O/Cu interface, coupling outward and inward oxide propagation.

• Why it matters: Oxide-scale growth is often treated as either outward cation diffusion or inward anion diffusion, but that dichotomy fails to explain how both interfaces can advance together in one oxidation event.
• What they did: The authors used in situ environmental transmission electron microscopy to directly monitor Cu oxidation and paired it with simulations to test a vacancy-mediated mechanism for coupled transport.
• The result: They find outward cation transport during surface growth injects a sustained vacancy flux into the underlying metal, enabling inward oxygen incorporation and driving buried-interface oxide growth, informing defect-regulated kinetic predictions.

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