Lunar Surface' Sputtering and Secondary Ion Mass Spectrometry

We combine laboratory and Apollo year on the moon) every surface species has been observations to describe the sputtering of the struck and subsequent ions eject chemicallylunar surface and the composition of the ejecta altered species. At high fluences sputtering with special reference to O. The atmospheric proceeds stoichiometrically (Johnson 1990). inventory appears to be dominated by microThree sputtering mechanisms occur. Electronic meteorite vaporization of lunar grains. sputtering (by ions, electrons, or EUV-photons) Sputtering effects are observable in the local results from excitation of electrons to repulsive plasma due to ion ejection, in the extended states and, for refractory-materials, applies to atmosphere through energetic neutral ejection, adsorbed species (H20, Na). Sputtering by and on grain surfaces through the chemical momentum-transfer is the dominant process for fractionation of the redeposited sputter-ejecta. solar wind ions. [Morgan & Shemansky (1990) Ionization of the micrometeorite-vapor also suggest the 0 yields are due to electronic contributes to the local plasma. sputtering' the cross sections, '10 -21 cm 2 are too small.] Finally, chemical sputtering arises Introduction after long-term bombardment or when bombarding with chemically reactive species (H, O, C). Apollo data indicated that solar-wind ions The total yield for oxides by low energy (0.1created amorphous outer layers on lunar grains 10 keV), light ions (H,He) are similar to metals '0.02•m, changed these grains isotopically and and peak near the energy-per-nucleon of the solar chemically and the energetic-ions created tracks wind' Ni peaks at 0.016 around 1.2 keV for H+; and spallation. These effects were used to for He + , Y = 0.2 atoms/ion at 2 keV, close to estimate regolith turnover rates. Because solar that for SiO 2 seen in Fig.(1). Since the solar wind-ions reach the surface, sputtering also wind has 5% He ++ , the contribution is of the occurs. We examine this here. Since microsame order as for protons. These yields increase meteorite bombardment modifies lunar grains with increasing angle of incidence having a