RF driven Microhollow Cathode Discharge for Atomic Emission Spectrometry

The microhollow cathode discharge is a multilayer system consisting of two metallic layers separated by a ceramic insulator. This microplasma was already implemented as element selective detector for emission spectrometry driven by a DC source. The discharge can be operated in the pressure range 10 mbar - 2 bar. The possibility to generate this plasma by a RF generator and a comparison with a DC plasma will be presented. The plasma is stable in noble gases, gas mixtures or air using RF or DC voltage. The RF generator is a low-power design and is utilizing common high-speed CMOS logic devices. The bridged push-pull circuit is operating in D-mode to take full advantage of low power dissipation. A resonance tank is formed of the multilayer system and a matching network to provide up to 900 Vpp for ignition and operation of the plasma. Atomic emission spectroscopy of the discharge was applied to the detection of chlorine and fluorine resulting from the decomposition of halogenated molecules introduced into the He plasma gas. The intensities are linear over three orders of magnitude. The detection limits for CCl2F2 are 20 ppb v/v using either Cl 912.114 nm or the F 739.868 nm.