Sputtering of water ice films: A re-assessment with singly and doubly charged oxygen and argon ions, molecular oxygen, and electrons

Abstract

We studied the erosion rates from thin water ice films on a microbalance upon irradiation with ions (O⁺, O₂⁺, O²⁺,Ar⁺, and Ar²⁺) and electrons at energies between 0.1 keV and 80 keV. The results with O⁺ and Ar⁺ irradiation confirm previous results of other research groups that relied on the same experiment set-up. In addition, we assessed how the ice film thickness affects the results and we compared the results for singly versus doubly charged ions and for O⁺ versus O₂⁺ ions. The irradiation with 1 keV and 3 keV electrons offer the first experimental results at these energies. Our results confirm theoretical predictions that the yield per impacting electron does not increase with energy ad infinitum but rather levels off between 0.1 and 1 keV. The results for ion and electron sputtering have important implications for atmosphere-less icy bodies in a plasma environment. We briefly discuss the implications for the icy moons of Jupiter. Finally, the experiments also allow us to assess the viability of two methods to measure the erosion rate in the case that the icy sample cannot be attached on a microbalance. This is an important step for future laboratory studies where regolith ice samples and their reaction to particle irradiation are to be characterized.