Focusing and defocusing in electron scattering along atomic chains

We investigated the degree of forward focusing and of multiple-scattering-induced defocusing for electrons in the keV range along regular chains of different atomic density in GaAs and GaP single crystals. The intensity angular anisotropy of elastic and inelastic (losses) Auger electrons was measured in the primary-beam diffraction-modulated electron-emission approach. In variance to the photoelectron-diffraction (PD) case, the possible influence of the energy-loss mechanism on the observed anisotropy can be disregarded and the in-depth distribution of the scattered intensity is independently determined. Both the focusing and defocusing lengths were found to be significantly larger than in previously reported PD results, and strongly dependent on the interatomic spacing. A comparative study of defocusing along the Ga [110] chains in GaAs and GaP gives experimental evidence of the influence of nearest-neighbor atomic rows (As and P, respectively) on the scattering processes.