The properties of a pulsed radio frequency capacitive discharge are investigated at atmospheric pressure in argon. The discharge can operate in two different modes: a homogeneous glow discharge or turn into filaments. By pulsing the 13.56 MHz generator both the filamentary and the glow modes can be selected depending on the pulse width and period. For a 5 µs pulse width (∼70 RF cycles in the pulse), short pulse periods (less than 100 µs) result in a filamentary discharge while long pulse periods (greater than 1 ms) result in a glow discharge. Optical emission spectroscopy and power measurements were performed to estimate the plasma temperature and density. Water vapour was introduced to the discharge as a source of hydrogen and the Stark broadening of the Balmer H β line was measured to allow the plasma density to be estimated as 10 15 cm −3 in the filamentary mode. The estimation of the glow mode density was based on power balance and yielded a density of 5 × 10 11 cm −3. Emission line ratio measurements coupled with the Saha equation resulted in an estimate of electron temperature of approximatively 1.3 eV for the glow mode and 1.7 eV for the filaments. Using the glow mode at a duty cycle of 10% is effective in decreasing the hydrophobicity of polymer films while keeping the temperature low.

A new collisional-radiative model for atmospheric-pressure low-temperature argon discharges is proposed, which illustrates the significant effect of electron density on the excited atom population distribution. This makes it possible to determine the electron density from the intensity ratio of emission lines of excited atoms. Results of this new method in several types of atmospheric-pressure discharges are found to be in agreement with those of the Stark broadening method and the electric model over a wide electron density range 10 11 -10 16 cm −3 .

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