On the origin of the LEIS signal in TOF- and in ESA-LEIS

The ion fraction analysis of 4He+ ions backscattered from various faces of copper single crystals is performed by using time-of-flight (TOF) and electrostatic analyzer (ESA) low-energy ion scattering (LEIS) techniques. When an experiment that integrates over 2π azimuth (typical ESA-LEIS setup) is used, the yield of ions backscattered from the Cu(1 1 0) surface may be given by projectiles penetrated much deeper than just one or two monolayers. The threshold energy for reionization processes for 4He+ and Cu found earlier by TOF-LEIS is experimentally confirmed by ESA-LEIS.