Backscattering effects in modulated electron emission from ultrathin overlayers

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