Mineral surface modification induced by low energy ion irradiation: Implications for solar-wind exposure effects in lunar soil

We performed ion irradiation on olivine and ilmenite to simulate solar-wind exposure effects in lunar soil. The surface morphology and microstructure after ion irradiation were characterized by field emission scanning electron microscopy. Sputtering erosion significantly modified the surface of irradiated Luobusha olivine grains. All irradiated grains show smooth surface and round shape. The cleavage fractures on the unirradiated olivine surface were widened and deeply etched after He⁺ irradiation. Both of these are the consequence of ion sputtering erosion. There are no bubbles or voids foundin the irradiated olivine grains, because He⁺ dose in this study is lower than saturated fluence. Irradiated Panzhihua ilmenite grains are all covered with smooth flakes with the thickness of about 400 nm. The formation of the flakes should be related with helium bubbles and their growth during He⁺ implantation. Some columnar-shaped particles are found at the surface of irradiated Panzhihua ilmenite. We speculate that these particles should be sulfide because of significantly high sulfur contents.