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INSTITUTE OF PHYSICS PUBLISHING PLASMA SOURCES SCIENCE AND TECHNOLOGY Plasma Sources Sci Technol 14 2005 314 320 doi 10 1088 0963 0252 14 2 013 Comparison of an atmospheric pressure radio frequency discharge operating in the and modes X Yang1 M Moravej1 G R Nowling1 S E Babayan2 J Panelon2 J P Chang1 and R F Hicks1 1 2 Chemical Engineering Department University of California Los Angeles CA 90095 USA Surfx Technologies LLC 3617 Hayden Ave Culver City CA 90232 USA E mail rhicks ucla edu Received 23 July 2004 Published 22 March 2005 Online at stacks iop org PSST 14 314 Abstract The and modes of an atmospheric pressure radio frequency plasma have been investigated The plasma source consisted of two parallel electrodes that were fed with helium and 0 4 vol nitrogen The transition from to was accompanied by a 40 drop in voltage a 12 decrease in current and a surge in power density from 25 to 2083 W cm 3 Optical emission confirmed that sheath breakdown occurred at the transition point The maximum light intensity shifted from a position 0 25 mm above the electrodes to right against the metal surfaces The average density of ground state nitrogen atoms produced in the atmospheric plasma was determined from the temporal decay of N2 B emission in the afterglow It was found that 5 2 and 15 2 of the N2 fed were dissociated into atoms when the plasma was operated in the and modes respectively The lower efficiency of the discharge may be attributed to the non uniform distribution of the discharge between the electrodes Some figures in this article are in colour only in the electronic version 1 Introduction Plasma technologies play a vital role in materials processing for the microelectronics automotive aerospace and biomedical industries Chemically reactive plasma discharges are widely used for etching thin film deposition surface activation and bio sterilization 1 2 Recently there has been increased interest in using atmospheric pressure plasmas for materials processing 3 15 These

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