PRIMARY-BEAM DIFFRACTION MODULATED ELECTRON-EMISSION (PDMEE) FOR SURFACE STRUCTURAL-ANALYSIS

Scattering interference of primary exciting electrons leads to a dependence of the Auger emission intensity on the beam incidence angle. For beam energy in the kiloelectron-volt range, maxima in the Auger yield occur when the primary beam is aligned with low-index crystal axes, therefore the Auger angular intensity distribution directly reflects the symmetries and the degree of local order. We investigated the potential for this effect, primary-beam diffraction modulated electron emission (PDMEE) to be used for surface structural characterization, in comparison with the Auger electron/photoelectron diffraction (AED/PD) technique. The angular intensity distributions of both low and high kinetic energy Auger electrons were measured on both GaAs and InP (110) surfaces. We show, by using highly collimated energetic electron beams, that the angular resolution is significantly improved in PDMEE with respect to AED/PD. Unlike the AED/PD case, the angular intensity distribution is independent of the kinetic energy of the Auger electrons, therefore low-energy, surface-sensitive electrons also directly reflect crystal symmetries, owing also to the fact that the specific momentum character of the Auger electrons can be neglected. Anisotropy in the intensity angular distribution as large as 70% was measured, comparable to AED/PD anisotropy values. Both a retarding field (low-energy electron diffraction optics) and a dispersion field cylindrical mirror analyser were used for PDMEE analysis, and instrumental performances are discussed comparatively.