Electron emission for grazing impact of keV He atoms on an Al(1Â 1Â 1) surface

The energy loss of He atoms with energies E ⩽ 28 keV scattered from Al(1 1 1) under a grazing angle of incidence is recorded in coincidence with the number of electrons emitted in the collision. From our data we deduce the mean energies for emission of a specific number of electrons during impact of the atomic projectiles. We observe that only a fraction of some percent of the energy transferred to metal electrons results in their emission. The mean energy for emission of electrons in head-on binary collisions of He atoms with conduction electrons is estimated from a simple classical model which describes the data fairly well. For higher energies of the projectile motion with respect to the surface normal, i.e. collisions with surface atoms under smaller impact parameters, the mean energy transfer to emitted electrons is enhanced which is attributed to an electron promotion mechanism.