Valence-electron energy loss near edges, truncated slabs, and junctions

Valence losses in electron microscopy can be conveniently computed using cl assical dielectric excitation theory. In many practical situations, the pre sence of complex structures gives rise to the possibility of coupling betwe en interface modes, surface modes, and edge modes. In the nonrelativistic c ase, the losses in such geometries can be calculated by taking a distributi on of surface and interface points, each of which is associated with an int erface charge. These charges interact self-consistently with each other as well as with the charge of the incident electron. Here, we have applied thi s boundary charge method to provide scanning transmission electron microsco py energy loss spectra near-edged structures such as truncated slabs and ju nctions formed by several media. We find the dominant modes associated with such systems and study their contribution to the characteristic energy los s functions. The significance of these excitations compared with the planar interface peaks is discussed in terms of the sample geometry with illustra tions for the cases of an MgO cube and an Si/SiO2 thin-film interface. [S01 63-1829(99)00939-X].