Using high-angle-annular-dark-field (HAADF) scanning-transmission-electron microscopy (STEM), we have investigated η-precipitates in the Al-Zn-Mg-Cu (AA7050) aluminium alloy. The HAADF STEM images taken along the zone axes of [101 ̅ 0]η, [12 ̅ 10]η, and [0001]η illustrated the projected atomic-scale configurations of η-MgZn2 crystal. The precipitates developed in layer-by-layer growth, supplied with precursors such as Zn, Cu, and Mg, which were solute atoms segregated around the η/Al interfaces due to the higher lattice strain energy. Stacking faults and defect layers composed of flattened hexagons were frequently observed along the zone axes of [12 ̅ 10]η and [101 ̅ 0]η, respectively, and their formation was elucidated, similarly taking into account the layer-by-layer growth. Occasional coalescence between two precipitates yielded a complicated boundary or a twin-like boundary.Based on the differences in orientation relationships between η-types and the Al matrix reported to date, two new types of η precipitates have been recognized and named η4' and η12.

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The aim of this work is to investigate the particle size and morphology of the nanocrystals in the non-volatile memory device by annular dark field (ADF) scanning transmission electron microscopy (STEM) and conventional transmission electron microscopy (CTEM) techniques. With respect to TEM investigation, statistical analysis on STEM image can acquire the size and density of nanocrystals more accurately than on TEM image. In addition, ADF STEM images successfully provide powerful evidences revealing the structure of IrO x nanocrystals as a core shell structure, where the inner structure is rich in Ir and the outer area is abundant in O or Al. This method could be one of the efficient way for examining the nanocrystals with a complicated cored structure.

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