Local symmetry and bonding effects on electron energy-loss near-edge structures: Ab initio study of an NiAl grain boundary

Electron energy-loss near-edge structure (ELNES) reflects an unoccupied, site-, and angular-momentum-projected density-of-states. Using a focused electron probe, one can measure the local electronic structure at atomic spatial resolution at defects such as grain boundaries. We have calculated partial densities of d states and L3 ELNES of Ni atoms at a Σ3 (111) grain boundary in B2 NiAl using the full-potential linearized augmented plane-wave method, carrying out ab initio structural relaxations. We observe large changes in the partial density of d states for Ni atoms near the boundary, which can be related to broken symmetry and reduced cohesion. These changes manifest themselves also in the Ni L3 ELNES, which measures the unoccupied density of Ni d states. The characteristic signal should be measurable experimentally at atomic spatial resolution on a spherical-aberration-corrected scanning transmission electron microscope. A spatially averaged interfacial signal should be measurable using a larger probe on a conventional instrument. The importance of carrying out electronic structure calculations in order to understand ELNES from grain boundaries is emphasized.