Electronic sputtering of solid N$_2$ by swift ions
Résumé
Most sputtering yield measurements for solid N 2 are reported for stopping powers lower than 10 −13eV cm 2 /molecule. We measured the sputtering yield for solid N 2 at stopping powers, in the electronic regime, above 10 −12eV cm 2 /molecule, extending the range of such measurements by more than an order of magnitude, using a 33 MeV 58 Ni 9+ swift heavy ions beam. The evolution of the thin N 2 ice films was monitored in-situ by mid-infrared spectroscopy (FTIR) during irradiation. As N 2 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 N 2 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 N 2 ice film and its dependence with the ice thickness for thin film conditions, monitoring the N 2 ice sputtering depth. We combine the results with previous measurements at lower stopping powers to derive the electronic sputtering of solid N 2 over a large stopping power range.
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