Sputtering of LiF(100) with low energetic Ne⁺ and Ne²⁺ ions

D. Wutte, U. Diebold, M. Schmid and P. Varga

Nucl. Instrum. Methods Phys. Research B 65 (1992) 167-172

Sputtering of a LiF(100) surface by singly and doubly charged Ne ions with impact energies between 10 and 500 eV has been performed. The emission of Li⁺, Li⁰, F⁺, F⁰ and LiF⁺ was measured by means of a quadrupole mass spectrometer. The yield of sputtered Li⁺ ions and Li⁰ atoms decreases with decreasing impact energy and is slightly higher for Ne²⁺ compared to Ne⁺ at impact energies below 100 eV. The situation changes very drastically regarding the emitted F particles. In the whole energy range investigated, the F⁺ and F⁰ yield was about one order of magnitude larger if Ne²⁺ projectiles were used instead of Ne⁺. According the experimental data we propose following model for the emission of F⁺: (1) The F^- ion of the solid surface is changed to F⁺ by Auger neutralization of the Ne²⁺ into Ne⁺ or by double resonance transition into doubly excited states of Ne⁰ with subsequent autoionization into Ne⁺. These processes takes place several Ångström in front of the surface. (2) The initial repulsive forces between the F⁺ ion and the surface are changed into attractive ones within a very short time by rearrangement of the alkali halide lattice. (3) The neutralized projectile sputters the F⁺ as in a normal sputtering event on a surface with low surface binding energy, and F⁺ can be emitted as long as the kinetic energy of the projectile is sufficiently high.

Corresponding author: P. Varga (varga).