ELECTRONIC EFFECTS IN LOW-ENERGY ION SPUTTERING OF LIF

Sputtering of a LiF(100) surface by singly (He and Ar) and doubly charged rare gas ions (Ar) with impact energies between 20 and 500 eV has been performed. The emission of Li+, Li0, F+ and F0 was measured by means of a quadrupole mass spectrometer. The yield of sputtered Li+ ions and Li0 atoms decreases with decreasing impact energy and becomes slightly higher for Ar++ compared to Ar+ at impact energies below 100 eV. The situation changes very drastically when looking at the emitted F particles. In the whole energy range investigated, the F+ and F0 yield was more than one magnitude larger for Ar++ as projectiles than for Ar+. Furthermore, for He+ bombardment a higher yield was observed than for Ar+. Therefore an electronic effect has to be assumed which causes enhancement of the sputtering of F+ if projectiles with larger potential energy are used. However, for He+ below 100 eV impact energy, a drastic decrease for the F+ yield was observe-which indicates that F+ emission cannot be due to a pure electronic effect. Our proposed model includes formation of F+ by Auger neutralization (if energetically possible) of projectiles in front of the target, and emission of the F+ ion due to momentum transfer in the collision with the already neutralized projectile.