Influence of a square pulse voltage on argon-ethyl lactate discharges and their plasma-deposited coatings using time-resolved spectroscopy and surface characterization

By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (T-e) 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 T-e, n(Ar-m), and discharge current is evaluated and correlated with the chemistry and the topography of 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 mu s, 30 mA, 0.3 eV). The n(Ar-m) values seemed to be rather stable around 10(11) cm(-3) with a sinus power supply. In contrast, with a pulse power supply with long time off (i.e., time without discharge) between each pulse, a progressive increase in n(Ar-m) from 10(11) cm(-3) up to 10(12)-10(13) cm(-3) was observed. When the time off was reduced, this increase was 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.