Abstract

60th Gaseous Electronics Conference (GEC), Meeting of The American Physical Society, in Arlington, Virginia (USA)

Investigations of negative oxygen ions in pulsed rf plasmas

MICHAEL KATSCH1, ALEXANDER WAGNER1 and MICHAEL KRÄMER2
1 University of Duisburg-Essen
2 Ruhr-University, Bochum

The spatial and temporal distributions of electrons and ions in ICP GEC reference cell and a large diffusion chamber connected to a helicon plasma source were investigated. The investigations were focussed on the production and loss processes of negative oxygen ions in argon-oxygen mixtures. Laser-induced photodetachment of the negative oxygen ions using of a frequency-doubled Nd:Yag laser along with a Langmuir probe was applied to detect the O- ions. An increase of the negative ion density in the early afterglow is found at high plasma densities in the GEC cell as well in the diffusion chamber. There is, apparently, a formation channel for negative ions that becomes efficient with reduced electron temperature. Dissociative attachment of electrons to highly excited metastable oxygen molecules are suggested as a negative oxygen ion source. Comparative measurements of the temporal behavior 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 supports the experimental results.