KINETIC ELECTRON-EMISSION IN KEV ION-SURFACE COLLISIONS

KeV ions interacting with a solid surface give rise to kinetic electro n emission. We will present measured and calculated absolute electron spectra for protons grazingly incident on a single crystal Cu surface at different azimuthal angles of incidence. The total electron emissio n amounts to approximately 1 electron per incoming ion and consists pr edominantly of low-energy electrons, with an exponentially decreasing intensity towards higher energies. For these specific incidence condit ions, the ions are first neutralized at relatively large distances abo ve the surface, followed by a series of mainly large impact parameter collisions closer to the surface. Recently we have shown that the domi nant mechanism for kinetic electron emission arises from the time depe ndent perturbation of weakly bound localized electrons occurring durin g each of these collisions. Our calculations for different azimuthal a ngles of incidence, and therefore for different impact parameter distr ibutions reproduce our measurements quite well. We also show that the contribution of this mechanism to the stopping power of keV ions scatt ering off a solid surface is considerable.