Atmospheric pressure microwave-powered microplasma source based on strip-line structure

Abstract

Summary form only given. Portable low cost microplasma sources are of interest for various applications such as materials processing, treatment of biomedical materials, chemical analysis and optical radiation sources. Microplasma sources are especially of interest for atmospheric pressure operation because they do not require a vacuum system. Further, by using higher frequency energy (microwave) to power the microplasma discharge, erosion of electrodes is reduced or essentially eliminated. Another feature of microplasmas is the high power density and plasma density of the discharges. Additionally, the gas temperature of microdischarges is lower than larger plasmas at atmospheric pressure. In this investigation a microwave powered microplasma system based on a double-strip-line structure is developed for the generation of atmospheric pressure plasmas with various feed-gases and feed-gas mixtures. The microplasma system is constructed with the top and bottom copper strip-lines separated by a dielectric material. The strip-line structure is powered at one end and the plasma is formed at the other end where the two copper strip-lines are brought together to a gap with 250 microns separation. The feed-gas is flowed through a channel in the dielectric such that it exits with the feed-gas flowing into the gap created by the two strip-lines. The gas flow channel in the dielectric is 250 microns high by 6 mm wide. The flow rate is varied from 900-2400 sccm. Argon and argon-oxygen microplasma discharges are formed in the gap between the two copper strip-lines. In argon-oxygen plasmas investigated, the oxygen percentage is varied from 1% up to 5%. The microwave power used for the discharges varies from 5 to 60 Watts. Images of the plasma are taken to show the shape, volume and intensity of the microplasmas. Optical emission spectroscopy is used to diagnose the discharges. The emissions from selected excited atomic and molecular oxygen species are measured. Other properties of the microplasma including gas temperature and electron temperature are also measured. Some experiments of etching diamond with argon-oxygen microdischarges will be presented.