Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions

Abstract

Pyroxenes ((Ca, Mg, Fe, Mn) 2 Si 2 O 6 ) belong to the most abundant rockforming minerals that make up the surface of rocky planets and moons. Therefore sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. In order to quantify this effect, sputtering of wollastonite (CaSiO 3 ) by He 2+ ions, which are seen as a very prominent contribution to solar wind potential sputtering, was investigated. Thin films of CaSiO 3 deposited on a quartz crystal microbalance were irradiated allowing precise in-situ real time sputtering yield measurements. Experimental results were compared with simulations with the code SDTrimSP, which were improved by adapting the used surface binding energy.On a freshly prepared surface He 2+ ions show a significant increase in sputtering compared to equally fast He + ions. The yield, however, decreases exponentially with fluence, reaching steady state at considerably lower values after sputtering of the first few monolayers.Experiments using Ar 8+ ions show a similar behavior and are qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, which is able to reproduce the observed potential sputtering behavior of both He and Ar very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. We conclude that the defect-mediated model of potential sputtering is also well-suited for CaSiO 3 .

Solar wind Helium ion interaction with Mg and Fe rich pyroxene as Mercury surface analogue

“…For sputtering on Mercury, the solar wind composition containing mostly H and He ions and the prominent He charge state He 2+ have to be taken into account. Due to its potential energy, He 2+ will cause additional particle release as a result of potential sputtering [8,10]. Specifically, Szabo et al investigated the potential sputtering of wollastonite (CaSiO 3 ) samples [8], which are similar to the samples used in the present experiments.…”

“…Due to its potential energy, He 2+ will cause additional particle release as a result of potential sputtering [8,10]. Specifically, Szabo et al investigated the potential sputtering of wollastonite (CaSiO 3 ) samples [8], which are similar to the samples used in the present experiments. They discuss the interplay between kinetic sputtering and potential sputtering with a solar wind composition of 96% H + and 4% 4 He 2+ ions.…”

“…Following the procedure described in detail in Ref. [8], the O surface binding energy was set to 6.5 eV and the parameter controlling the model of surface binding energies isbv = 2 used (see [16] for details on the simulation parameters). This set of parameters was found to describe sputtering of the structurally similar wollastonite sample very well and also allows to reproduce Ar + sputter yields for the pyroxene-based samples used in this study.…”

“…A detailed examination of the fluence dependence of He implantation however has not been conducted so far. More recent research focused on sputtering by solar wind ions and its contribution to exosphere formation [7][8][9].…”

“…By combining these techniques, implanted mass, saturation fluence and release temperature could be determined in-situ to get a better understanding of the interaction between the solar wind and Mercury's surface. Singly charged He ions were used for this purpose, as He 2+ causes additional potential sputtering [8,10], which was not the focus of the study.…”