Radio-frequency-driven near atmospheric pressure microplasma in a hollow slot electrode configuration

We report hollow electrode geometries that support near atmospheric (89 kPa) microdischarges in Ar and Ar-air mixtures when excited at 13.56 MHz with rf voltages of 50-230 V. The slot dimensions are 200 mum wide by 400-600 mum deep and 3-35 cm in length. Optical emission along the slot length is uniform in intensity at applied rf power levels up to 10 W/cm of slot length under the experimental conditions described herein. When metal electrodes are employed, we can draw 0.18 A/cm of self-bias dc current into the rf-driven plasma. Measurements of the electrode self-bias dc voltage level indicate operation in both negative as well as positive self-bias discharge modes. The latter mode, to our knowledge, has not been reported previously in rf microdischarges at near atmospheric pressures. (C) 2003 American Institute of Physics.