Angular dependence of the sputtering yield of water ice by 100 keV proton bombardment

Abstract

We measured the total sputtering yield of amorphous water ice for 100 keV H + as a function of the projectile incidence angle, and the angular distribution of the ejected H 2O and O 2 molecules, using a quartz-crystal microbalance and mass spectrometry, respectively, at temperatures of 20 K and 100 K. The total sputtering yield follows a cos − f θ dependence, with f ≅ 1.3, regardless of the irradiation temperature. This is explained by the action of fast binary δ-electrons that relocate the electronic energy deposited by the ion near the surface into the bulk of the material. We found that the O 2 emission follows a cosine dependence, as expected from isotropic collision cascades or if transport of the oxygen to the surface is by thermal diffusion. In contrast, H 2O emission is more outward peaked than cosine, which could be attributed to the blocking of large angle emission by the transient crater formed during sputtering of multiple water molecules by a given projectile.