Properties of a non-equilibrium atmospheric pressure plasma

Summary form only given. Non-equilibrium atmospheric pressure plasmas are of interest for the surface treatment, cleaning, etching and deposition of materials. We have characterized the properties of a radio-frequency atmospheric pressure plasma fed with helium or argon and up to 2.0 vol% nitrogen. The electrodes consisted of two parallel plates, 0.5 cm/sup 2/, separated by a gap of 1.6 mm. At a current and voltage of 0.26 A and 229 V, the gas undergoes partial ionization, entering the abnormal glow regime. The current and voltage increased with the applied power to maximum values of 0.41 A and 317 V. The power consumed by the plasma at this point was 2.4 W. Further increasing the power caused the plasma to shift into a new discharge mode, in which one of the sheaths appeared to break down. Here the current and voltage ranged from 0.33 to 0.27 A and 202 to 220 V before it returned to the abnormal mode with decreasing power. In this mode, the maximum power consumed by the plasma was 50 W. The density of nitrogen atoms produced in the abnormal and high-power glow discharges was determined by measuring the temporal decay rate of the first-positive emission of nitrogen molecules, i.e., N/sub 2/(B)/spl rarr/N/sub 2/(A)+h/spl nu/. It was found that the abnormal glow at 30 W/cm/sup 3/ and 1.3 vol% N/sub 2/ in He produced 1.0/spl times/10/sup 16/ cm/sup -3/ N atoms. This corresponded to dissociation of 1.7% of the N/sub 2/ molecules. By contrast, the high-power mode with a maximum power density of 2600 W/cm/sup 3/ and 0.4 vol% N/sub 2/ in He generated 1.7/spl times/10/sup 16/ cm/sup -3/ N atoms. This is equivalent to 8.4% dissociation of the N/sub 2/. Note that the neutral gas temperature measured in the abnormal and high-power glow discharges equaled 75 and 250/spl deg/C, respectively. These results indicate that both operating modes of the plasma are effective at dissociating molecules into reactive species. A thorough discussion of the physics and chemistry of the atmos- heric plasma will be provided at the meeting.