Paper SS-TuP10
Space Weathering Effects at the Surface of Thin-Film Aluminosilicate Model Regolith

Tuesday, October 23, 2018, 6:30 pm, Room Hall B

Space weathering effects on volatile-rich airless bodies have been studied far less extensively, than those anhydrous interfaces. Although the presence of volatile resources has been established by recent space exploration missions, the fundamental physics and chemistry behind volatile formation and sequestration, associated with radiation processing of regolith, is yet to be thoroughly explored. Therefore a systematic and integrated study of the effect of radiation processes on regolith is needed to better understand the fundamental driving forces governing the volatile transformation at the interface of such bodies. Accordingly, the overall goal of the project is an in situ study of regolith, irradiated with laboratory-based sources within a UHV system, mimicking solar wind processes on airless bodies in space.

To carry out this work, our group is leveraging established thin-film recipes to generate and characterize a well-ordered regolith simulant within our multi-purpose UHV system. Herein we use aluminosilicate (Al_xSi_yO_z) sheets as model regolith. The Al_xSi_yO_z film will be grown on a ruthenium (Ru) substrate via sequential PVD of Al and Si in the presence on O₂. The Ru is cleaned with repeated Ar⁺-sputtering/annealing. XPS and He⁺ ISS have been used for cleaned Ru to ensure surface cleanliness (no detectable contaminants) and LEED for long-range crystal order (sharp 1x1 hexagonal pattern). Initial silica (SiO₂) thin-film growth has been employed to establish both coverage and oxidative crystallization temperature. Using the calibrated Si flux and relative XPS sensitivity factors, Al flux will be calibrated, and both will be used to create bilayer Al_xSi_yO_z film. In addition to the XPS, ISS and LEED, atomic scale confirmation of planar/crystalline silicate layers will be provided by STM analysis.

To simulate solar wind processing of model regolith, we will use irradiation facilities available in our lab, such as an electron gun, an ion gun, and an X-ray source. The physical and chemical characterization of radiation-induced defects to the fabricated Al_xSi_yO_z sheet (like those previously reported by others for SiO₂ film) will be investigated with the in-house equipment. Previously established experiments used to investigate SiO₂ will be helpful to study the electron-stimulated desorption of volatiles. In addition, Al_xSi_yO_z film transference to other supports will be attempted in support of collaborative efforts with others.

Our methods encompass surface science methodologies for radiation investigation on regolith samples, which will help to minimize the gaps in knowledge related to space weathering effects on the airless bodies.