Negative oxygen ions in a pulsed RF-discharge with inductive coupling in mixtures of noble gases and oxygen

Abstract

We report on the spatio-temporal behaviour of negative oxygen ions in a pulsed inductively coupled RF excited discharge in oxygen noble gas mixtures. With a high fraction of noble gas admixtures and at high power an increase in the negative ions is observed in the early phase of the afterglow. This indicates a generation channel of negative ions that becomes effective with decreasing electron temperature. Dissociative attachment of electrons to highly excited metastable oxygen molecules is suggested as a negative oxygen ion source. Comparative measurements of the temporal behaviour of the negative ions in Ar/O2, Kr/O2 and Ne/O2 mixtures indicate that metastable noble gas atoms do not play an essential role in the formation process of negative ions during the afterglow. A simple global model for the negative oxygen ion density supports the experimental results. The model is based on sound experimental data such as the atomic oxygen density and the quench rates by molecular oxygen of the metastable noble gas atoms.