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Fig. 4


Sputtering yield Y sp (left) and Γ (right), as a function of incident ion energy for surface binding energies of Eb = 1 eV (red) and Eb = 0.1 eV (blue); and, x = mimn ≈ 0.15 (solid), ≈ 0.81 (dash), ≈ 1.5 (dot-dash) and ≈ 2.1 (dot). Typically the target species range from light H atoms to heavier Mg2 SiO4 molecules, to encapsulate this range the geometric mean of the potential target masses was calculated as kg). Therefore, for this constant value of mn the range of x plotted cover ion masses mi = 4.0026u (He) to mi = 55.845u (Fe), covering the expected range of ionic masses in the atmosphere. The regime Γ > 1 (the sputtering regime) is signified by a grey shaded area. For comparison the energy of ions at the surface of the dust grain, Esf (Fig. 3), for Te = 1 eV and Te = 10 eV when fe = 1 (the degree of ionisation, fe = ne ∕(nn + ne)), are over-plotted (grey-solid).

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