A quantitative simulation of ion beam sputtering and related collision cascade effects is essential for applications of ion beam irradiation in thin film deposition, surface treatment and sculpting with focused ion beams, ion beam smoothing of surfaces and ion-induced nanopattern formation. The understanding of fundamental ion-solid interaction processes relevant for nanostructure formation, ion-induced mass redistribution, sputter yield amplification, ion beam mixing and dynamic compositional changes requires reliable simulations of ion-solid interaction processes in particular at low ion energies.In this contribution we discuss the possibilities, the key benefits and the limitations of three popular binary collision Monto Carlo simulation programs (SDTrimSP, TRIDYN and SRIM).The focus will be set to the calculation of angle dependent sputter yields, angular distribution of sputtered particles, sputter yields for compound materials, sputter yield amplification effects, as well as the extraction of parameters relevant for modelling ion-induced surface pattern formation from vacancy and recoil atom distributions.
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 .
The effect of sputtering yield enhancement by implantation of noble gases into solid silicon is investigated with the Monte Carlo program SDTrimSP. The process of diffusion is incorporated into the program to describe the outgassing of noble gases. The bombardment of Si with He, Ne, Ar, Xe at normal incidence is studied in the energy range from 1 to 500 keV. Good agreement of the calculated results with experimental data is found.
The sputtering of wollastonite (CaSiO3) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at glancing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H + bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to H + bombardment only.
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