Kinetic electron emission (KE) for grazing scattering of H, He, Ne, and Ar ground state atoms with keV/amu impact energies on clean monocrystalline atomically flat Al and Cu surfaces has been studied in coincidence with projectile energy loss. Measured KE yields are subject to a clear impact energy threshold, in agreement with a free electron gas model description for the target electron momentum distribution (''classical'' KE threshold). For smaller projectile scattering angles corresponding to larger distances of closest approach to the surface, this classical KE threshold is shifted to higher impact energies. By measuring KE threshold energies for different projectile scattering angles, we have probed the effective electron surface potential.
For scattering of Ne and Ar atoms, a very weak electron emission is observed below the classical KE threshold, which within a more realistic description of the electron momentum distribution for the target surface can be ascribed to higher electron momenta.
Grazing projectile scattering also permits a practically non-destructive surface structure determination, because a considerably larger number of electrons is emitted when changing from planar to axial surface scattering ''surface triangulation''.