Electronic sputtering by swift highly charged ions of nitrogen on amorphous carbon

Abstract

Electronic sputtering with heavy ions as a function of both electronic energy loss d E/d x and projectile charge state q was studied at the French heavy ion accelerator GANIL. Amorphous carbon (untreated, and sputter-cleaned and subsequently exposed to nitrogen) was irradiated with swift highly charged ions ( Z=6–73, q=6–54, energy 6–13 MeV/u) in an ultrahigh vacuum scattering chamber. The fluence dependence of ion-induced electron yields allows to deduce a desorption cross-section σ which varies approximately as σ∼(d E/d x) 1.65 or σ∼ q 3.3 for sputter-cleaned amorphous carbon exposed to nitrogen. This q dependence is close to the cubic charge dependence observed for the emission of H + secondary ions which are believed to be emitted from the very surface. However, the power law σ∼(d E/d x) 1.65, related to the electronic energy loss gives the best empirical description. The dependence on d E/d x is close to a quadratic one thus rather pointing towards a thermal evaporation-like effect.