The influence of the input voltage frequency (35 and 150 kHz), interelectrode gap (1 and 2 mm) and precursor concentration (250, 350, and 450 ppm) on the electron temperature (Te), number density of metastable Ar atoms (n(Ar m )), and discharge current density (proportional to the electron density ne) is studied in an argon-ethyl lactate dielectric barrier discharge (DBD). An argon-ammonia Penning mixture is also considered as reference. These results are correlated to the chemistry (XPS, IR) and topography (AFM) of the ethyl-lactate-based plasma polymer coatings. Low Te values from 0.3 to 0.5 eV were obtained for all discharges. This observation, in addition to resemblances with the Ar-NH3 mixture, suggested that the ionization kinetics of ethyl lactate-based discharges is driven by Penning reactions. Among the investigated parameters, the dissipated power obtained through changes of the excitation frequency had the largest impact on both the coatings properties and the discharge behavior.

By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (Te) and number density of argon metastable atoms (n(Ar m)) were determined in argon-ethyl lactate dielectric barrier discharges. The influence of a square pulse power supply on Te, n(Ar m), and the discharge current is evaluated and correlated to the chemistry and the topography of the plasma-deposited coatings. Pulsed discharges were found to have shorter (100 ns) but stronger (1 A) current peaks and higher electron temperatures (0.7 eV) than when using a 35 kHz sinusoidal power supply (2 µs, 30 mA, 0.3 eV). The n(Ar m) values seemed rather stable around 10 11 cm-3 with a sinus power supply. On the contrary, with a pulse power supply with long time off (i.e. time without discharge) between each pulse, a progressive increase of n(Arm) from 10 11 cm-3 up to 10 12-10 13 cm-3 was observed. When the time off was reduced, these increases were measured in sync with the current peak. The chemical composition of the coatings was not significantly affected by using a pulse signal whereas the topography was strongly influenced and led to powder formations when reducing the time off.