Measurement of autoionization rates for electron emission above a metal surface

We present K Auger spectra arising from collisions of ${\mathrm{N}}^{6+}$ ions with a Ni(110) target for different kinetic energies and observation angles. The bulk of the electrons is ascribed to emission below the surface. At very low collision velocities (${\mathit{v}}_{\mathrm{\perp }}$≤${10}^{\mathrm{-}2}$ a.u.) we find a pronounced contribution from electrons emitted prior to impact. The velocity dependence of the above-surface component is used for the experimental determination of the time scales involved in electron emission above the surface. Comparison with theoretical estimates is also presented.