Resonant charge transfer in low-energy ion scattering: Information depth in the reionization regime

Abstract

Time-Of-Flight Low-energy ion scattering (TOF-LEIS) experiments were performed for He+ ions scattered from Cu(100) and Cu0.5Au0.5(100). Probabilities for resonant neutralization and reionization in close collisions were deduced in a wide energy range. To learn about the information depth in LEIS, in a next step ion spectra were analyzed for polycrystalline Cu samples. The relative yield of backscattered projectiles, which have undergone distinct charge exchange processes, was calculated. Results indicate a strong contribution to the ion yield that origins from particles reionized in a close collision in deeper layers when experiments are performed at energies where reionization is prominent. The surface sensitivity of the ion signal at different energies is quantified. Based on these results, the total ion spectrum was quantitatively modelled by two consistent, but different approaches.

Role ofdelectrons in electronic stopping of slow light ions

“…For Pt, E th is considerably lower than for Ag, i.e., 700 eV for Pt, compared to 1200 eV for Ag. As has been observed for other materials, also in the present case resonant neutralization in a close collision is more effective than re-ionization in the vicinity of E th [29]; this conclusion is based on the observation that at E 0 > E th , P + is lower than expected from pure AN. The fact that for Pt, P + increases at primary energies E 0 > 1 keV points to an increased relative importance of re-ionization.…”

Temperature-dependent in-situ LEIS measurement of W surface enrichment by 250 eV D sputtering of EUROFER

“…However, an estimation of the magnitude of the error which is introduced by these sub-surface scattering events cannot be determined from the calibration spectrum and one has to rely on the facts that (i) the energy of those particles moves progressively away from the surface peak the deeper the scattering takes place [29], i.e. these ions do not contribute to the measured surface peak, and (ii) their number decrease rapidly with depth and limits the detected signal to a few monolayers with the dominant signal contribution originating from the topmost monolayer [22]. The ratio of the number of counts in the fitted W peak and the Fe spectrum is 4/3.…”

“…Even in those cases the decay length, i.e. the depth where the ion signal has decayed to 1/e is about 1 nm [22]. In the following we report on the investigation of W surface enrichment by 250 eV D sputtering of EUROFER steel and in-situ analysis of the W surface density using LEIS.…”

The helium atom in metallic electron gases: a comparative study based on screened Schrödinger Hamiltonians

“…For instance, proper calculations of matrix elements for single and double re-ionizations [5,6] in distance dependent collisions with lattice ions during penetration requires reasonably accurate knowledge of binding energies of electrons and wave functions around the slowly moving projectile. The present paper is devoted, on the theoretical side, to this important basic aspect of a more detailed understanding of slowing down processes where, in target-dependent [7] re-ionization, the kinetic energy of the projectile is decreased [5] due to promotion of the electronic bound state above the Fermi energy of a metal.…”