Model for direct ejection of diatomic molecules by collisional sputtering

Abstract

We present a simple collision model which describes the vibrational energy distributions and dissociation probability for diatomic molecules that are directly ejected by collisional sputtering. The results show that the probability that molecules survive sputtering without dissociation can be quite high (> 90%), and that monotonically decreasing vibrational distributions can often be expected, with a majority of the molecules in low vibrational levels ( n = 0,1,2, 3). The model provides a collisional explanation for the observation of Boltzmann-like vibrational distributions for sputtered molecules. The calculations show that the use of impulsive collision models can reasonably account for the relative yield of sputtered molecules. However, in order to predict vibrational energy distributions which are qualitatively correct, it is necessary to go beyond the impulsive approximation by explicitly allowing for the finite duration of collisions.