fig4

Figure 4. Cross-sectional STEM/EDS analysis of the oxidized Ni₅₄Mn₄₆ surface (650 K, 2.8 h). (A) HAADF image showing a tri-layer structure consisting of the surface oxide, Ni-rich intermediate layer, and NiMn substrate; (B) EDS elemental maps showing Mn enrichment in the surface oxide and relative Ni enrichment in the subsurface region; (C) EDS line-scan intensity profiles along the white dashed line in (A). STEM: Scanning transmission electron microscopy; EDS: energy-dispersive X-ray spectroscopy; HAADF: high-angle annular dark-field.