An experimental study of proton implantation in olivine

Abstract

Abstract The solar wind is a multi-ion flux that progressively modifies the composition and structure of near-surface domains in atmosphere-less solar objects, like asteroids. A bombardment of the target by different elements like hydrogen (H) at various energies (keV to MeV) causes, among other things, the implantation of solar wind particles in crystalline and amorphous materials. It is important to understand the mechanisms and features of this process (e.g., how much is implanted and retained), in order to constrain its contribution to the chemical budget of solar objects. Yet, there has been no detailed study on H implantation into olivine (e.g., the quantification of maximum retainable H), a major mineral in this context. We performed experiments on H implantation in San Carlos olivine at 10 and 20 keV with increasing fluences (up to 3·1018 at/cm²) to simulate solar wind irradiation. Nanoscale H profiles that result from implantation were analyzed using Nuclear Resonance Reaction Analysis after each implantation to observe the evolution of the H distribution as a function of fluence. We observed that after a systematic growth of the characteristic, approximately Gaussian shaped, H profiles with increasing fluences, a maximum concentration at H ~ 20 at% is attained. The maximum concentration is independent of ion energy, but the maximum penetration depth is a function of beam energy and is greater at higher energies. Based on these observations we were able to constrain the maximum retainable H in olivine as a function of ion energy.