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High-purity niningerite (MgS) was synthesized by BenchChem under vacuum conditions for use in laboratory simulations of solar-ion space weathering of sulfide minerals that are expected to be present on the surface of Mercury. MgS was initially characterized via x-ray photoelectron spectroscopy prior to investigations into the preferential loss of near-surface sulfur in niningerite with 2 keV H2+ irradiation. Survey and high-resolution (Mg 1s, Mg 2p, S 2p) x-ray photoelectron spectra of as-received magnesium sulfide powder (99.9%) are presented, including surface contaminants that originate from exposure to atmosphere (C 1s, O 1s). Minor impurities derived from sample synthesis (Al 2s, Al 2p) and packaging or processing (F 1s) are noted in the survey spectrum. 

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness. 

Key Points We irradiated samples of meteoritic troilite (iron sulfide) with H + and He + ions, simulating solar‐wind space weathering We observed nanoscale roughening of the surface and formation of a sulfur‐depleted layer as the irradiations progress Using SDTrimSP modeling in combination with X‐ray photoelectron spectroscopy, we quantify the surface oxide layer thickness, diffusion rate, altered‐layer composition, and fluence‐dependent sputtering yield