Pulsed RF discharges, glow and filamentary mode at atmospheric pressure in argon

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 νs pulse width (∼70 RF cycles in the pulse), short pulse periods (less than 100 νs) 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 10¹⁵ cm^-3 in the filamentary mode. The estimation of the glow mode density was based on power balance and yielded a density of 5 × 10¹¹ 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.