Microstructural investigation of the oxidation behavior of Cu in Ag-coated Cu films using a focused ion beam transmission electron microscopy technique

With the aim of elucidating a detailed mechanism for the oxidation behavior in submicron Cu particles coated with a thin Ag layer, the dewetting of Ag and the oxidation behavior of Cu in Ag-coated Cu films upon heating were investigated with a focused ion beam transmission electron microscopy technique. A slight dewetting of the Ag layer began at approximately 200 °C and aggregates of Cu₂O particles were formed on the Ag layer, indicating that the initial Cu₂O phase was formed on the thin Ag layer. Voids were formed in the Cu layer because of Cu atoms diffusing through the thin Ag layer to be oxidized in the upper Cu₂O aggregates. After being heated to 250 °C, the Ag layer became more irregular, and in some regions, it disappeared because of intensive dewetting. The number and average size of the voids also increased. At 300 °C, a hollow structure with a Cu₂O shell was formed. Pillar-like structures of unoxidized Cu and large voids were found under the Cu₂O layer.