Synthesis of crystalline phases in space silicate analogues with helium ion irradiation.

Abstract Silicate minerals such as "Mg-Fe-Si-O" compounds, are found in asteroids, planets, and cosmic dust grains in the interstellar medium. As the silicate dust grains traverse regions of space, they are irradiated by energetic ions, such as alpha particles, which can modify the crystalline phase of the mineral dust. Silicate dust grain analogues were synthesized using multiple low energy (<60 keV) ion (Fe−, Mg−, O−) implantations into a silicon wafer. The low energy ion beam as-implanted samples were cut into several smaller sections. Some of these low-energy as-implanted samples were further irradiated with a 600 keV helium ion beam at varying current densities (ions/unit area/unit time) and subsequent furnace annealed at 1000 °C temperature in Ar gas environment. The crystalline phases of the post annealed samples were monitored and reported as a function of current densities using x-ray diffraction (XRD). The XRD results showed an increase in the crystalline phases of olivine by the high-energy helium ion irradiation processing with a beam of current density of 500 nA/cm2. This work is relevant for space weathering processes as well as solid material evolution in astrophysical environments, especially asymptotic giant branch stars with an oxygen rich outflow. [ABSTRACT FROM AUTHOR]