Fermi momentum above metal surface from electrons ejected by impact of He atoms

Kinetic emission of electrons near its threshold is studied for grazing impact of keV He atoms on flat and clean Al(111), Al(110), and Cu(111) surfaces. We observe a defined dependence of the kinetic emission threshold behaviour on the scattering conditions. The data are analyzed in the framework of a classical model for electron emission based on momentum transfer in binary encounters between atomic projectiles and conduction electrons of the metal target. From the impact velocity dependence of kinetic emission yields near threshold we obtain information on momenta of Fermi electrons as a function of the distance from the surface and on the corresponding electronic surface potential. (authors)