Neutralization of low-energy Ne + colliding with Mo S 2 and metallic molybdenum: An experimental and theoretical study

Abstract

The neutralization probability in the scattering of Ne+ ions by a molybdenum disulfide semiconductor(MoS2) surface in a backscattering geometric configuration is experimentally and theoretically analyzed. Thelow-energy ion scattering technique was used to experimentally determine the neutral fractions of Ne projectilesbackscattered by the Mo atoms of the MoS2 target surface after a single collision. A high neutralization rate in thebackscattered projectiles (of the order of 95%) was obtained, practically independent of the projectile incomingenergy and the collision geometry. Additionally, the remaining dispersed ions were measured to be all positive,within the experimental error. An identical experiment was conducted on a polycrystalline metallic molybdenumsurface to assess for differences between the two target surfaces, with completely different electronic properties.A quantum-mechanical formalism was employed to theoretically describe the projectile-surface resonant chargetransfer during the binary collision of Ne projectiles with both surfaces. Our calculations show that the innerstates of Mo atoms play a central role in the resonant charge transfer in the Ne/MoS2 system. From thecomparison with the experimental results, we can conclude that the resonant charge transfer to the projectileground state is not sufficient to explain the large neutralization of the Ne projectiles observed for both surfaces.An Auger neutralization mechanism and resonant charge transfer to the excited states of the projectile areexpected to be particularly relevant for polycrystalline Mo and MoS2 target surfaces, respectively.