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Thin polycrystallineLiF films have been bombarded by slow ((1 keV) multicharged Ar~+ ions (q ( 9), in order to study the resulting total sputter yields by means of a quartz crystal microbalance.More than 99% of sputtered particles are neutral and show yields, at given impact energy, in proportion to the potential energy of projectile ions. The respective "potential sputtering" process already takes place far below 100 eV impact energy. It can be related to defect production in LiF following electron capture by the multicharged ions, and removes about one LiF molecule per 100 eV of projectile potential energy. PACS numbers: 79.20.Rf, 79.20.Nc, 79.90.+b Recently, Neidhart et al.[1] observed total sputter yields of about 0.5 LiF molecule per primary ion, for impact of rather slow ()5 eV) He+, Ne+, and Ar+ ions on polycrystalline lithium fluoride. Since for metal surfaces no sputtering takes place at such low impact energies, this sputtering of LiF has been related to "electronic effects" initiated by electron transfer from the LiF surface into projectile ions. F+ secondary ion yields resulting from impact of slow singly and doubly charged noble gas ions on LiF differ by more than 1 order of magnitude [2], which has been explained by the comparably more efficient Auger neutralization (AN) and/ or resonance neutralization (RN) from the LiF valence band into doubly charged ions. Generally, for impact of slow multicharged ions (MCI) on alkali halide surfaces a rapid increase of the secondary ion yields with projectile charge q has been demonstrated [3]. When etching a KC1 surface previously bombarded with slow Arq+ or Krq+ at given ion fluxes, higher charged ions turn out to cause larger etching patterns [4]. Based on such evidence, Bitenskii, Murakhmetov, and Parilis [5] have proposed a so-called "Coulomb explosion" sputter mechanism for insulators under slow MCI impact. Conceivably, this process should be initiated by the strong negative charge depletion in the uppermost target layers due to the rapid electron capture into incoming MCI, leaving behind positive target ion cores which then may push each other out of the solid. Sputtering of metals is exclusively caused by kinetic energy transfer from projectiles onto the target particles, producing nonthermal velocity distributions of sputtered particles with steeply decreasing yields below typically 500 eV impact energy [6]. Ion induced sputtering from alkali halides results in much slower (thermal) particle velocities, similarly as for electron and photon stimulated desorption (ESD and PSD) [7,8] from alkali halides. Only a small fraction shows comparably high velocities as for sputtering of metals. Most particles from ion induced sputtering of alkali halides are neutral [9], as for ESD and PSD. For the latter processes, recent studies [7,8] explain the observed, rather large neutral desorption yields by efficient creation of defects in the near surface region, which suggests that similar mechanisms may also account here for the interesting ion induced sputtering o...

The recently discovered phenomenon of potential sputtering, i.e., the efficient removal of neutral and ionized target particles from certain insulator surfaces due to the potential rather than the kinetic energy of impinging slow highly charged ions, has now also been observed for stoichiometric SiO 2 surfaces. Using a sensitive quartz crystal microbalance technique, total sputter yields induced by Ar q1 ͑q # 14͒ and Xe q1 ͑q # 27͒ ions have been determined for LiF and SiO 2 surfaces. The primary mechanisms for potential sputtering (defect mediated sputtering) and its considerable practical relevance for highly charged ion-induced surface modification of insulators are discussed. [S0031-9007(97)03627-2]

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The injection of 10-100 keV Lio diagnostic beams into magnetically confined fusion plasmas causes collisionally induced Lil emission at 670.8 nm, in close relation to the edge plasma electron dcnsity. A numcrical method Cor quantitative reConstruction of the plasma density exclusively from rclaliw Lil 670.8 nm emission profilcs as measured slang the diagnostic beam has been developed, involving all relevant collisional interactions of the Li atoms with plasma constituents. The applicahility of the descrihed algorithm is illustrated by experimental results obtained for the TEXTOR Tokamak edge plasma at KFA Jirlich.