1. Experimental Physics II - Reactive Plasmas, Ruhr University Bochum 1 , Bochum D-44780, Germany
2. Microsystems Technology, Ruhr University Bochum 2 , Bochum D-44780, Germany
3. Research Department Plasmas with Complex Interactions, Ruhr University Bochum 3 , Bochum D-44780, Germany