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2D atomic mapping of oxidation states in transition metal oxides by scanning transmission electron microscopy and electron energy-loss spectroscopy

Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn3O4. The Mn L(2,3) energy-loss near-edge structures from Mn2+ and Mn3+ cation sites are similar to those of MnO and Mn2O3 references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations.

Prospects for 3D imaging of dopant atoms in ceramic interfaces

Expanding upon recent experimental results for a Y-doped Sigma13 alpha-Al(2)O(3) grain boundary, we explore through simulation the extent to which plan-view imaging of buried interfaces may be possible (cf. the more usual cross-section imaging). As we show in detail, that case was significantly aided by the normal to the interface plane being a high-order zone axis orientation, giving the visibility of the Y atoms a remarkable insensitivity to the specimen thickness and the depth of the interface plane. The visibility along lower order zone axis orientations and the visibility of different dopant species are discussed.