Detection of a layer of Al₂O₃ at the interface of Al/MgAl₂O₄ by high-resolution observation using dual-beam FIB and TEM

The interface of aluminum and MgAl₂O₄ formed naturally during high-temperature oxidation of an aluminum–magnesium alloy was observed in high resolution in a bid to investigate heterogeneous nucleation of aluminum grains on MgAl₂O₄ particles. Scanning electron microscopy at an ultra-high magnification of 200,000× has clearly detected a thin intermediate layer of about 50 nm, which is conventionally too small to be detected by the microscopy, between aluminum and MgAl₂O₄. An electron-transmitting specimen was fabricated exactly on the layer in the same chamber without moving it for further sampling. Chemical analyses show that the intermediate layer is composed of aluminum and oxygen, i.e., Al₂O₃, which means that the thin Al₂O₃ layer prevents the direct contact of aluminum and MgAl₂O₄.