Model Calculations of Ion Induced Desorption Yields

The ion induced desorption is a severe luminosity limitation for low charge state heavy ion accelerators. Thus it was intensively investigated in dedicated experiments during the last years. It was shown that the ion induced desorption is a surface effect with a strong link to the substrate [1]. The overall quantity of desorbed gas during long term irradiation is always in the range of a monolayer (10 cm). From the geometrical cross section of the projectile desorption yields of η ≥ 100 molecules per incident ion can not be explained. Therefore we have developed a theoretical model to describe the ion induced desorption as a thermally moderated process using the inelastic Thermal Spike Model. The inelastic Thermal Spike Model has been developed to explain the processes of track formation and sputtering induced by heavy ions in energy ranges where the electronic energy loss is dominating [2]. First the projectile energy is deposited in the electronic subsystem of a sample. The hot electrons distribute the energy radially away from the ion path within typically 10 s. Especially in metals the free electrons moderate the energy deposition. After around 10 s the electronic system heats the lattice by electron-phonon coupling and after 10 s the sample approaches ambient temperature again. A computer code to calculate the time dependent radial evolution of the temperature of the electronic system as well as the lattice of metals was developed years ago. We have extended this code to describe the ion induced desorption as a thermally moderated process in terms of