SECONDARY-ION EMISSION FROM LITHIUM-FLUORIDE UNDER IMPACT OF SLOW MULTICHARGED IONS

Secondary ion emission has been investigated for bombardment of polycrystalline lithium fluoride by slow multicharged Ar ions (charge state q less than or equal to 9, impact energy E(k) less than or equal to 500 eV). The F- ions originate from collisional energy transfer, almost independent of the primary ion charge, whereas the F+ yield strongly increases with q. The F+ ions are produced via interatomic Auger transitions from the F- 2p valence band into projectile states, and their desorption from LiF is controlled by Coulomb interaction of F+ with Li+ and F- surface ions, and LiF lattice relaxation. At high impact energy, emission of Li+ is also mainly due to collisional energy transfer, but toward lower E(k) the primary ion charge plays an increasingly important role. The present measurements demonstrate that secondary ions account for less than 0.1% of our earlier measured total sputter yields from LiF.