Electron Emission from Insulators Irradiated by Slow Highly Charged Ions

Abstract

Total electron emission yields have been measured for the first time resulting from impact of slow highly charged Arq+ (q ≤ 17), Xeq+ (q ≤ 50) and Hgq+ (q ≤ 68) ions on clean insulating LiF(001) and CaF2(111) surfaces at various impact angles. The surprisingly large yields show that even for the highest projectile charge states, a local charge-up of the surface poses no barrier for electron emission. We demonstrate that this is due to a strong sub-surface contribution in the potential electron emission process which is considerably more efficient in insulators because of the increased inelastic mean free path and the production of secondary electrons

Highly charged ion induced nanostructures at surfaces by strong electronic excitations

“…The electron yields for all insulating targets show a rather high contribution of kinetic electron emission compared to the metallic surface of Au, reproducing the findings in [18].…”

“…(5) and (6) nicely reproduce the yields on the insulating surfaces down to velocities as low as 3:5 Â 10 4 m/s (E kin ¼ 20 eV/Q), more than one order of magnitude below the velocities accessible in [18]. Thus, it seems that the proposed mechanisms of increased contribution of sub-surface created electrons for insulators hold promise even at lowest projectile velocities.…”

“…(3) charge exchange and energy loss measurements are necessary [15,16], whereas determining the right side requires knowledge about the total secondary electron yield N e [17,18] and electron energy distribution E e;i [9,19] as well as yield and energy distribution of emitted X-rays. The term E surf =exc is accessible by calorimetric measurements in experiments and can eventually be extracted from simulations [9,20].…”

“…It was unclear until a few years ago whether an insulating surface could even deliver enough electrons on typical time scales of HCI neutralization in the order of several 10-100 fs. Meissl et al [18] recently demonstrated that even for highest charge states (Q 6 68 (Hg ions)) no saturation of the electron yield with increasing projectile charge occurs at the surfaces of LiF(0 0 1) and CaF 2 (1 1 1). These measurements further revealed that the total electron yields from insulators show similar or even higher values compared to a (metallic) Au (1 1 1) surface although the latter one has a much lower work function.…”

“…To provide experimental access to this open question we performed measurements of the electron yields from the surfaces of LiF(001), KBr(0 0 1) and CaF 2 (1 1 1) at lowest ion velocities and charge states of up to Q ¼ 40 at the Two Source Facility of the Ion Beam Center at the Helmholtz-Zentrum Dresden-Rossendorf. The setup for measuring the total electron emission yield is based on the one used in [18] (detailed information can be found elsewhere [45,46]). Fig.…”