Experimental study of ELNES at grain boundaries in alumina: intergranular radiation damage effects on Al-L23 and O-K edges.

The need for understanding the structural and chemical properties of interfaces and grain boundaries in materials is being paralleled by new developments in transmission electron microscopy methods. The extraction of data on grain boundaries has to be carefully evaluated, freed from artefacts and allowing fairly direct interpretation. Besides improvements in data processing, a primary requirement is an improved knowledge of the ELNES fine structures of the relevant absorption edge. For the case of alumina, we first present a compilation of Al-L(23) edges with an energy resolution of 0.5-0.6eV. This allows identification of the ELNES features which are more likely to vary as a function of the aluminium atomic environment, i.e. the excitonic peaks between 77 and 79eV and the near-edge features between 83 and 86eV, which both clearly depend on the Al site environment. Our second investigation concerns the likely occurrence of electron radiation damage at interfaces which may adversely interfere with the identification of new bonding types. The Al-L(23) and O-K ELNES changes associated with several cases of damage are detailed.