A stable glow plasma at atmospheric pressure has been achieved for plasma treatment under selected conditions, for example the structure of electrodes, the kind of dilute gas, and the frequency of power. The surface fluorination of PET film and carbon thin-film deposition by such a plasma is described here. The surface energy can be controlled by plasma treatment of various concentrations (O2/CF4/He) in the same way as the lower pressure method that has been reported by Kogoma and co-workers (1987). Active species in plasma are identified by emission spectroscopy.

Some reasons are discussed for the stabilisation of a glow discharge at atmospheric pressure which was attained by controlling the following three conditions: the use of a high-frequency source, the use of He gas for dilution and the insertion of a dielectric plate between electrodes.The three conditions interact: the dielectric plate in a plasma forms the pulsed discharge from a low-frequency source, the fast duration of pulse current prevents a transition to an arc style discharge and a large volume of metastable atomic helium aids ionisation or dissociation near the electrode plate and in the flowing gas.The measurements of discharge-maintaining voltage at several hundred volts provide evidence that this is really a glow plasma at atmospheric pressure. The changes of the emission intensities of metastable helium prove indirectly that some dissociation occurs as a result of the action of the helium atom.

Recently the authors developed an atmospheric-pressure glow discharge plasma method which can be applied to surface treatment and deposition on insulating surfaces for purposes of large-scale system treatment. However, this method was not able to treat metallic substrates. Consequently, they have improved the upper electrode to enable metal substrates to be treated. Some organic films were polymerised by the atmospheric-pressure method. Comparison of results from the atmospheric-pressure glow plasma method with those obtained by the low-pressure glow plasma method showed no differences in the chemical structures of plasma-polymerised films.

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