Potential sputtering: desorption from insulator surfaces by impact of slow multicharged ions

Abstract

For certain target species, sputtering by slow multiply charged ions strongly depends on the primary ion charge state. In contrast to the usual ballistic sputtering it is not the kinetic but rather the potential energy stored in multiply charged ions that leads to this novel form of ion-induced sputtering (“potential sputtering”). A series of recent careful experiments is summarized where potential sputtering has been investigated for hyperthermal highly charged ions impact on Au, Si, GaAs, SiO 2, MgO, LiF, and NaCl. Only for alkali halides (LiF, NaCl) and to some extent for SiO 2 an enhancement of the total sputter yield, which is measured by a quartz crystal microbalance technique, with increasing charge state of the primary ion could be observed. All other targets showed only the common (collision induced) kinetic sputtering. With a defect mediated desorption model as known from electron stimulated desorption we can explain why potential sputtering is exclusively found for insulators with strong electron–phonon coupling.