Backscattering of Li+ ions from MoS2: Probing charge transfer through experiment and theory

Abstract

We present a combined experimental and theoretical study of charge exchange dynamics in low-energy Li+ collisions with a MoS2 surface, focusing on the neutralization of backscattered projectiles. Using low-energy ion scattering, we measure charge-state-resolved time-of-flight spectra for incident energies between 2.5 and 8.0 keV, under different scattering geometries and azimuthal orientations. The results reveal neutralization fractions ranging from 20% to 35% for projectiles scattered from Mo atoms, with a slight but reproducible increase with increasing energy. These values correspond exclusively to single binary collisions between Li and Mo atoms, with negligible formation of negative ions and no significant dependence on azimuthal or entrance/exit angles. The experimental results are interpreted using a time-dependent resonant charge transfer model based on the Anderson Hamiltonian in the infinite-U limit. The model incorporates the interaction of the Li 2s level with the Mo-projected local density of states, calculated within a bond-pair formalism. Theoretical predictions reproduce well the magnitude of the measured neutral fractions, although they underestimate their energy dependence at higher energies, an effect possibly related to the omission of excited-state channels such as the Li 2p level. A qualitative comparison with charge transfer involving sulfur atoms reveals consistent trends but a systematic overestimation by the model, likely due to reionization effects in complex multi-atom trajectories. These results demonstrate the importance of local electronic structure in charge exchange processes and highlight the need for extended models that include excited states and multi-site interactions.