DIFFRACTION AND FOCUSING EFFECTS IN THE ELASTIC-SCATTERING OF ELECTRONS FROM CU(001)

We have measured polar-intensity plots (PIP's) of the elastic reflection of electrons from Cu(001) in the energy range 200-1500 eV. At low energies, the PIP's present sharp peaks due to low-energy electron diffraction. For E > 500 eV, strong peaks appear at the angles corresponding to the main crystallographic axes. We interpret this as being due to the focusing effect that occurs in Auger and x-ray photoelectron diffraction. The importance of this finding is that both the reciprocal and the real (direct) lattices can be explored in the same experiment by simply varying the energy of the electrons.