Radio frequency hollow cathode source for large area cold atmospheric plasma applications

A new type of radio frequency (rf) large area non equilibrium ('cold') plasma source operating at atmospheric gas pressures in an open reactor was presented. The source was based on a specially designed rf electrode with the gas flowing through an inner microstructure integrated in the electrode. A cylindrical source of 35 mm in diameter with approximately 900 hollow cathodes forming an integrated open structure and a rectangular 120 X 20 mm(2) source of this type were tested. A typical rf power for the source operation is only several tens of watts. Experiments show that the performance of both sources at atmospheric pressure was substantially better in comparison with single cylindrical rf hollow cathodes of 400 mum in diameter. The argon and neon plasmas generated in the space between the main electrode and the substrate holder were uniform and very stable. The optical emission spectroscopy study, the rf current, voltage and impedance measurements, as well as the substrate temperature tests reveal three different power dependent regimes of these plasma sources. Effects of plasma treatment of surfaces were studied on both temperature sensitive samples (plastic webs) and metals (aluminum, steel). An effective cleaning of Al samples was observed after 5 min treatment in the neon plasma in an open reactor. After 1 s treatment of the Polyethylene web the surface tension increases from values < 34 mN/m to values 56 mN/m. Design of sources allows their direct scaling up and may bring a number of interesting applications in large area cold atmospheric plasma processing. (C) 2000 Elsevier Science B.V. All rights reserved.