Local symmetry and bonding effects on electron energy-loss near-edge structures: Ab initio study of an NiAl grain boundary - art. no. 205117

Electron energy-loss near-edge structure (ELNES) reflects an unoccupied, si te-, and angular-momentum-projected density-of-states. Using a focused elec tron probe, one can measure the local electronic structure at atomic spatia l resolution at defects such as grain boundaries. We have calculated partia l densities of d states and L-3 ELNES of Ni atoms at a Sigma3 (111) grain b oundary in B2 NiAl using the full-potential linearized augmented plane-wave method, carrying out ab initio structural relaxations. We observe large ch anges in the partial density of d states for Ni atoms near the boundary, wh ich can be related to broken symmetry and reduced cohesion. These changes m anifest themselves also in the Ni L-3 ELNES, which measures the unoccupied density of Ni d states. The characteristic signal should be measurable expe rimentally at atomic spatial resolution on a spherical-aberration-corrected scanning transmission electron microscope. A spatially averaged interfacia l signal should be measurable using a larger probe on a conventional instru ment. The importance of carrying out electronic structure calculations in o rder to understand ELNES from grain boundaries is emphasized.