L-shell filling of N⁶⁺ and O⁷⁺ ions from a clean and LiF-covered Au(111) surface

We report on a high-resolution Auger spectroscopy study of the interaction of N⁶⁺ and O⁷⁺ 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 O⁷⁺ than for N⁶⁺ 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 KLL electrons are emitted at an early stage of the interaction.