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.