Determining the stopping power of low kinetic energy Ne+ projectiles in self-Assembled monolayers

Neutral impact collision ion scattering spectroscopy (NICISS) is used to measure the energy loss in organic self-assembled monolayers (SAMs) on Au using Ne⁺ with low kinetic energies from 3 to 5 keV. With increasing film thickness, the energy loss of the projectiles increases because the projectile experiences more collisions with target atoms.

Through comparing Monte-Carlo simulations with the NICISS experiments, it was found that contributions from nuclear stopping for Ne⁺ were significantly larger than for He⁺ mainly due to the stronger contribution of small-angle scattering of Ne⁺ making Ne NICISS unsuitable for depth profiling at energies of 5 keV or lower. The measured Ne⁺ electronic stopping in SAMs is small despite the large atomic number of Ne. Comparing experiments and DFT calculations shows that the latter accurately reproduce stopping powers for Ne⁺, while SRIM overestimates the stopping power. This contrasts He⁺ ions, where DFT and SRIM align closely with experiments.