FOCUSING AND DEFOCUSING IN ELECTRON-SCATTERING ALONG ATOMIC CHAINS

We investigated the degree of forward focusing and of multiple-scatter ing-induced defocusing for electrons in the keV range along regular ch ains of different atomic density in GaAs and GaP single crystals. The intensity angular anisotropy of elastic and inelastic (losses) Auger e lectrons was measured in the primary-beam diffraction-modulated electr on-emission approach. In variance to the photoelectron-diffraction (PD ) case, the possible influence of the energy-loss mechanism on the obs erved anisotropy can be disregarded and the in-depth distribution of t he scattered intensity is independently determined. Both the focusing and defocusing lengths were found to be significantly larger than in p reviously reported PD results, and strongly dependent on the interatom ic spacing. A comparative study of defocusing along the Ga [110] chain s in GaAs and GaP gives experimental evidence of the influence of near est-neighbor atomic rows (As and P, respectively) on the scattering pr ocesses.