Focusing-defocusing of keV electrons along [001] and [101] Fe atomic chains

We have investigated the focusing and defocusing process of a primary electron wave along Fe atomic chains. To this end, we measured the intensity of the LVV Auger signal, as a function of the incidence angle of the primary beam, from a Co him buried in a Fe matrix. We found that maximum focusing efficiency takes place for six scatterers along [001]Fe atomic chains, then defocusing starts to set in. However, a significant anisotropy is still detectable at eleven scatterers deep in the bulk. The anisotropy depth profile we measured has been used to evaluate the anisotropy in more complex situations, such as thin films and multilayers.