Microplasmas: physics and application to the production of singlet oxygen O₂(a¹Δ_g)

Laboratoire de Physique des Gaz et des Plasmas, CNRS et Université Paris-Sud, 91405 Orsay Cedex, France

Corresponding author: vincent.puech@pgp.u-psud.fr

Received: 6 July 2007
Revised: 22 August 2007
Accepted: 4 September 2007
Published online: 7 December 2007

Abstract

Microplasmas refer to electric discharges created in very small geometries able to operate in DC mode at high pressure without glow to arc transition. The recent and considerable interest in microplasmas is due to their unique properties in term of discharge stability and power loading. A microplasma configuration which has proven to be stable at atmospheric pressure and up to a power density of some 100 kW/cm³ is the Micro Hollow Cathode Discharge (MHCD) developed by Schoenbach and coworkers. MHCDs are created by applying a voltage between two closely spaced hollow electrodes separated by a dielectric layer. The thickness of the dielectric and the diameter of the hole are both on the order of some 100's microns. These MHCDs can be used as plasma cathodes for generating a diffuse discharge between the MHCD cathode and a third positively-biased electrode placed some distance away. This is the so-called Micro Cathode Sustained Discharge (MCSD) configuration, which can be operated as a non self-sustained discharge. In that mode, the MCSD appears as a unique tool for producing, at high pressure, large fluxes of O₂(a¹Δ_g) metastable states which cannot be efficiently produced in classical self-sustained discharges. Based on experimental works performed by our group and on modeling studies done by Pitchford and coworkers at Toulouse University, this paper summarizes the properties of the plasmas generated by the MHCD and the MCSD, with an emphasis on the new fascinating opportunities for the production of O₂(a¹Δ_g) metastable states by electrical discharges in high pressure rare gas-oxygen mixtures.