Although grain boundaries are known to dominate the bulk properties of many technologically important materials, in most cases there is no fundamental atomic scale understanding of why they should have such an effect. One of the problems in developing this understanding is that conventional structure determination techniques, such as phase contrast imaging in TEM or Z-contrast imaging in STEM, produce only a 2-dimensional projection of the crystal structure. Atomic scale compositional changes must be simulated and a unique interpretation is clouded by boundary reconstructions and strain effects. Furthermore, neither technique provides any information on the local changes in the electronic structure that are critical for both the electrical and mechanical properties of the boundary.
EELS provides a means to quantify local changes in both composition and electronic structure. However, without a knowledge of the structure, interpretation of any observed changes at grain boundaries is extremely difficult.