ATOMIC-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY IN CRYSTALLINE SOLIDS

In this paper we discuss the incoherent imaging of crystals under zone axis conditions at atomic resolution, comparing the conditions necess ary with elastically and inelastically scattered electrons. In both ca ses, for a weakly scattering object, it can be shown that collecting a ll scattered electrons will lead to an incoherent image, a convolution of the probe intensity profile with an appropriate elastic or inelast ic object function. In the elastic case we show how the ''hole-in-the- detector'' problem is circumvented by use of an annular detector with a sufficiently large inner radius. In the inelastic case, a theorem du e to Ritchie and Howie first indicated the feasibility of incoherent i maging at atomic resolution. We discuss the object function for this c ase using a hydrogenic model developed by Maslan and Rossouw, which in dicates that atomic resolution is possible for losses above a few hund red eV. Probe channeling is found to be a central concept in extending the validity of these weak scattering results to the important case o f thick crystals. This allows us to demonstrate atomic resolution spec troscopy experimentally at a CoSi2/Si(111) epitaxial interface using t he Co L-loss.