L-shell filling ofN6+andO7+ions from a clean and LiF-covered Au(111) surface

Abstract

We report on a high-resolution Auger spectroscopy study of the interaction of ${\mathrm{N}}^{6+}$ and ${\mathrm{O}}^{7+}$ ions with a clean and a LiF-covered Au(111) target. The electron spectra from collisions on Au(111) and LiF-covered Au(111) are distinctly different. The ones resulting from the interaction with Au(111) covered with one monolayer of LiF resemble spectra taken on bulk LiF, which, in contrast to LiF-covered Au(111), is an insulator. On the Au(111) surface and for scattering geometries preventing projectile penetration below the first atomic layer, a more efficient L-shell filling for ${\mathrm{O}}^{7+}$ than for ${\mathrm{N}}^{6+}$ ions is observed. Surprisingly enough, for a single monolayer of LiF on Au the total K Auger intensity of nitrogen is nearly 30$%$ larger as compared to the clean Au(111) target, while for oxygen no enhancement is found. These findings demonstrate that, for specific projectile-target systems (e.g., N-LiF), an efficient mechanism that fills the projectile L shell is active well before the projectiles reach the surface, so that $\mathrm{KLL}$ electrons are emitted at an early stage of the interaction.