Stuttgart 2012 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

P: Fachverband Plasmaphysik

P 6: Grundlegende Phänomene

P 6.2: Hauptvortrag

Montag, 12. März 2012, 17:00–17:30, V57.01

Negative ions and mode transitions in oxygen cc-rf plasmas — •Kristian Dittmann, Christian Küllig, and Jürgen Meichsner — Ernst-Moritz-Arndt-University of Greifswald, 17489 Greifswald

The formation and presence of negative ions have a strong influence on plasma kinetics in low-temperature reactive plasmas. In particular, negative ions significantly determine the charged species balance and the electron energy distribution function. Laser photodetachment and microwave interferometry at 160 GHz is combined for the analysis of negative atomic oxygen ions in the bulk plasma of an oxygen cc-rf discharge. Two modes are measured characterized by different electronegativity α = n₋/n_e. High electronegativity with α > 2 is associated with low decay time constant of few µ s, only, wheras for low electronegativity, α < 1, the relaxation of electron density needs much longer with typical decay time constants up to about 100 µ s. With increasing rf power the mode transition show a step-like behavior. Additionally, phase resolved optical emission spectroscopy measurements combined with particle-in-cell simulations show a strong influence of the negative atomic oxygen ions on the α-γ-mode transition of the discharge. Finally, the role of the negative ions related to the attachment-induced ionization instability in oxygen cc-rf plasmas will be discussed. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the Sonderforschungsbereich Transregio 24 ’Fundamentals of Complex Plasmas’.