Philipp Sichler

High frequency glow discharges at atmospheric pressure with micro-structured electrode arrays

Micro-structured electrode (MSE) arrays allow the generation of large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. The electrode widths, thicknesses and distances in the micrometre range are realized by means of modern micro-machining and galvanic techniques. The electrode distance, the gap width d, is small enough to generate sufficiently high electric field strengths to ignite gas discharges by applying only moderate radio frequency (RF, 13.56 MHz) voltages (80–390 V in Ne, He, Ar, N2 and air). The non-thermal plasma system is characterized by a special probe measuring the electric parameters. We tested MSE arrays with d = 70, 25 and 15 µm. The MSE driven plasmas show a different behaviour from conventional RF discharge plasmas. Due to the very small electrode gap width we can describe the behaviour of the charged particles in the RF field of our system with the dc Townsend breakdown theory, depending on the pressure range and gas. With decreasing pressure, the gas discharges, especially in Ne and He, are increasingly dominated by field electron emission. With the MSE arrays as plasma sources several applications were developed and successfully tested, e.g. decomposition of waste gases and sterilization of food packaging materials at atmospheric pressure.

Micro-structured electrode arrays: atmospheric pressure plasma processes and applications

Abstract Micro-structured electrode (MSE) arrays allow to generate large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. The electrode dimensions in the micro-range realized by means of modern micro-machining and galvanic techniques are small enough to generate sufficiently high electric field strengths to ignite gas discharges applying only moderate radio frequency (13.56 MHz) voltages (80–390 V in Ne, He, Ar and N 2 ). The non-thermal plasma system is characterized by a special probe measuring the electric parameters. Possible industrial applications of the MSE arrays are plasma chemistry (e.g. waste gas decomposition) and surface modification of materials. Using an MSE based micro-reactor the abatement of the greenhouse gas CF 4 was performed with decomposition rates of over 90% at a pressure of 100 mbar in He and N 2 . The decomposition of waste gases in the plasma was monitored online with quadrupole mass spectrometry. At atmospheric pressure in He the abatement rate of CF 4 is still over 70%. Other applications realized in our lab are thin film deposition of diamond-like carbon layers and SiO 2 layers on various substrates and sterilization of food packaging materials.