Electronic sputtering of solid N[formula omitted] by swift ions

Abstract

Most sputtering yield measurements for solid N2 are reported for stopping powers lower than 10−13eV cm2/molecule. We measured the sputtering yield for solid N2 at stopping powers, in the electronic regime, above 10−12eV cm2/molecule, extending the range of such measurements by more than an order of magnitude, using a 33 MeV 58Ni9+ swift heavy ions beam. The evolution of the thin N2 ice films was monitored in-situ by mid-infrared spectroscopy (FTIR) during irradiation. As N2 is only weakly infrared active, and can be hardly monitored directly via an infrared absorption mode in such experiments, we use the Fabry–Perot interference fringes of the ice film to evaluate, via an optical model, the erosion of the N2 film as a function of ion fluence. A sputtering model including several sputtering crater shapes is developed and tested against experimental data. We derive the sputtering yield for a semi-infinite N2 ice film and its dependence with the ice thickness for thin film conditions, monitoring the N2 ice sputtering depth. We combine the results with previous measurements at lower stopping powers to derive the electronic sputtering of solid N2 over a large stopping power range.