Evidence for above-surface and subsurface neutralization during interactions of highly charged ions with a metal target

The projectile K Auger electron emission observed during grazing collisions of 60-keV ${\mathrm{N}}^{6+}$ ions with Au(110) is characterized by two components with strikingly different dependences on perpendicular velocity. A ‘‘fast’’ component dominates and is ascribed to ‘‘subsurface’’ emission. This component was satisfactorily modeled using a Monte Carlo simulation of the projectile trajectories after surface penetration. A ‘‘slow’’ component appears at very small angles and has a time dependence characteristic of the neutralization-deexcitation cascade predicted to occur above the surface prior to bulk penetration.