Characterization of reactive plasmas with catalytic probes

Reactive plasmas are nowadays widely used for processing of different materials including the technologies of discharge cleaning, plasma activation, plasma etching, cold ashing, plasma sterilization, and plasma-synthesis of nanostructured materials. The most important parameter in such plasmas is often the density of neutral atoms. One of the best tools for real-time measurements of the O, H and N atom density is a catalytic probe. The probes take advantage of catalytic heterogeneous surface recombination of neutral atoms. Due to high recombination coefficients of the catalytic tip, the probes are heated to a high temperature during exposure to highly dissociated gas such as reactive plasma. The catalyst temperature depends on the flux of neutral atoms on the probe tip. Using mathematical formalism it is possible to calculate the density of neutral atoms in the probe vicinity from measured temperature. The probes give rather accurate results in a broad range from about 1019 to 1022 m− 3. The probes were successfully applied to measure the density of neutral atoms in hydrogen, oxygen and nitrogen plasmas as well as in plasmas created in mixture of these gases with noble gases. Several examples of application are presented. Advantages and limitations are presented and discussed as well.