Plasma-assisted deposition at atmospheric pressure

Most plasma-assisted deposition methods currently available use gas discharges at pressures below 1 hPa. In many cases, the process temperature can be kept low due to the fact that the energy necessary for the initiation of chemical reactions is transferred via charged particles. However, a low pressure requires a large amount of vacuum equipment. Processes at atmospheric pressure are more favourable if results similar to those of existing methods can be achieved. Barrier discharges provide the basis for a new plasma-assisted deposition method at atmospheric pressure. These 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 properties 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 mu m are obtained if trains of voltage pulses are used. The 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.