Effect of surface binding energy on molecule sputtering

Abstract

The sputtering of molecules from a solid surface induced by energetic ion impact is studied. Specifically, a scenario is considered where diatomic molecules close to the target surface obtain a kick from a recoil atom in the ion-induced collision cascade. The change in their translational, rotational and vibrational energies due to the passage of the surface barrier is calculated. Two extreme cases are studied. (i) The molecular centre of mass is bound to the surface. The internal degrees of freedom are then not affected by the surface barrier. (ii) The surface binding acts separately on each atom of the molecule. Classical perturbation theory then shows that translational and rotational energy are changed in a complicated manner, depending on the molecular orientation and the emission angle. Vibrational excitation passes the surface barrier adiabatically.