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

Scattering interference of primary exciting electrons leads to a depen dence 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, t herefore the Auger angular intensity distribution directly reflects th e symmetries and the degree of local order. We investigated the potent ial for this effect, primary-beam diffraction modulated electron emiss ion (PDMEE) to be used for surface structural characterization, in com parison with the Auger electron/photoelectron diffraction (AED/PD) tec hnique. The angular intensity distributions of both low and high kinet ic energy Auger electrons were measured on both GaAs and InP (110) sur faces. We show, by using highly collimated energetic electron beams, t hat the angular resolution is significantly improved in PDMEE with res pect to AED/PD. Unlike the AED/PD case, the angular intensity distribu tion is independent of the kinetic energy of the Auger electrons, ther efore low-energy, surface-sensitive electrons also directly reflect cr ystal symmetries, owing also to the fact that the specific momentum ch aracter of the Auger electrons can be neglected. Anisotropy in the int ensity angular distribution as large as 70% was measured, comparable t o AED/PD anisotropy values. Both a retarding field (low-energy electro n diffraction optics) and a dispersion field cylindrical mirror analys er were used for PDMEE analysis, and instrumental performances are dis cussed comparatively.