Plasma-Assisted Deposition at Atmospheric Pressure

In plasma-assisted deposition methods the activation energy necessary for the initiation of chemical reactions is transferred via charged particles. Due to this fact in many cases the process temperature can be kept small, if gas discharges at pressures below 1 hPa are used. On the other hand low pressure requires a great deal of vacuum equipment. Processes at atmospheric pressure are more favourable, if similar results compared to existing methods can be achieved. Basis for a new plasma-assisted deposition method at atmospheric pressure are barrier discharges. Those discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated. Starting with some basic considerations on the repetitive generation of microdischarges, the deposition of thin polymeric films on glass surfaces is described, using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained, if trains of voltage pulses are used. Parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.