Vanishing influence of the band gap on the charge exchange of slow highly charged ions in freestanding single-layer MoS2

Abstract

Charge exchange and kinetic energy loss of slow highly charged xenon ions transmitted through freestanding monolayer MoS2 are studied. Two distinct exit charge state distributions, characterized by high and low charge states, are observed. They are accompanied by smaller and larger kinetic energy losses, as well as scattering angles, respectively. High charge exchange is attributed to two-center neutralization processes, which take place in close impact collisions with the target atoms. Experimental findings are compared to graphene as a target material and simulations based on a time-dependent scattering potential model. Independent of the target material, experimentally observed charge exchange can be modeled by the same electron capture and de-excitation rates for MoS2 and graphene. A common dependence of the kinetic energy loss on the charge exchange for MoS2 as well as graphene is also observed. Considering the similarities of the zero band-gap material graphene and the 1.9 eV band-gap material MoS2, we suggest that electron transport on the femtosecond timescale is dominated by the strong influence of the ion's Coulomb potential in contrast to the dispersion defined by the material's band structure.