Application of the catalytic probe method for measuring the concentration of oxygen atoms in Ar/O2 plasma of a low-pressure arc

Abstract

The monitoring of the degree of oxygen dissociation in the discharge plasma is critical for various plasma applications associated with the etching and oxidation of surfaces or the reactive deposition of oxide coatings. The use of existing measurement techniques is limited owing to their complexity, significant error rate, or application conditions. This study deals with the development of a catalytic probe method for measuring the degree of oxygen dissociation in dense arc discharge plasma. A method for measuring and processing the experimental results is presented, which allows the determination of the thermal contribution of the heterogeneous recombination of oxygen atoms at a high total heating power of the catalytic probe by particle streams and plasma radiation. The atomic oxygen concentration was measured in low-pressure arc plasma with a self-heating hollow cathode in an Ar/O2 mixture with changes in the discharge current and oxygen partial pressure over a wide range of 30–70 A and 0.2–0.6 Pa, respectively. It has been demonstrated that the maximum degree of oxygen dissociation (up to 25% of the O2 content) is achieved at the maximum discharge current and is practically independent of the oxygen flow, whereas the highest concentration of atomic oxygen is achieved when the maximum current and O2 flow values are combined. This conclusion is important for technologies based on plasma-chemical processes in high-current discharges.