Backscattering effects in modulated electron emission from ultrathin overlayers

The intensity of the Auger emission from ultrathin (< 2 monolayers) overlay ers excited by energetic (1-5 keV) electron beams, shows an unusually large anisotropy as a function of the incidence angle. We proposed a multistep m echanism which accounts for this anisotropy, based on the electron focusing and backscattering of the beam electrons from the bulk atoms. The intensit y and anisotropy of the backscattered electrons has been measured in a larg e energy interval and its relationship with the structure and the Auger emi ssion from the surface layer is discussed.