Sputtering of Ices by High Energy Particle Impact

Electronic excitation of thin films of molecular and rare gas solids by MeV He and H ions is efficient in causing sputtering. The sputtering yields vary widely for different species, even for those with very similar surface binding energy. The sputtering yields for CO, Ar, and N,, for example, differ by a factor of 10. Even more striking for these three is the dependence of the sputtering yield on the electronic stopping power of the bombarding particle. The dependence is found to be quadratic for CO, linear for Ar and it exhibits a linear-to-quadratic transition in N,. The experimental results indicate the importance of the specific routes for nonradiative electronic deexcitation and the importance of cooperative effects associated with neighboring excitations produced along the tracks of individual bombarding particles.