Velocity distributions of particles sputtered from supported 2D-MoS$_2$ during highly charged ion irradiation

TL;DR

This study investigates how highly charged ions cause particle emission from supported 2D-MoS$_2$ during irradiation, revealing distinct velocity distributions linked to kinetic and potential energy effects, and highlighting electron-phonon coupling as a key mechanism.

Contribution

It provides the first detailed analysis of velocity distributions of sputtered particles from 2D-MoS$_2$ under highly charged ion impact, distinguishing effects of kinetic and potential energy.

Findings

Two main velocity contributions linked to kinetic and potential effects.

Potential sputtering primarily involves electron-phonon coupling.

Interaction mechanisms are independent for slow highly charged ions.

Abstract

The interaction of highly charged ions (HCI) with solids leads to particle sputtering, which can be used for defect-mediated engineering of the properties of the material. Ions can store energy in the form of kinetic and potential energy (sum of the ionization energies) and transfer it to the solid upon impact. The interaction and sputtering mechanisms depend significantly on the projectile energies. However, the relevance of various interaction mechanisms is unknown. Here we show that for slow HCI (5 keV) the interaction mechanisms leading to particle emission by electronic excitation and transferred kinetic energy are independent from each other, which is consistent with our atomistic simulations. We have irradiated substrate supported (Au, SiO$_2$) monolayers of MoS$_2$ with highly charged xenon ions (charge state: 17$+$ - 40$+$), extracted the emitted neutral, post-ionized Mo particles into a time-of-flight mass spectrometer and determined their velocity distributions. We find two main contributions, one at high velocities and a second one at lower velocities, and assign them to kinetic and potential effects respectively. Our data suggests that the dominant mechanism for potential sputtering is related to electron-phonon coupling, while non-thermal processes play no significant role. We anticipate that our work will be a starting point for further experiments and simulations to determine whether the different processes resulting from E$_{pot}$ and E$_{kin}$ can be separated or whether synergistic effects play a role.