Abstract
Atmospheric-pressure diffuse dielectric barrier discharges (DBDs) were obtained in Ar/O2 gas mixture using dual-frequency (DF) excitation at 200 kHz low frequency (LF) and 13.56 MHz radio frequency (RF). The excitation dynamics and the plasma generation mechanism were studied by means of electrical characterization and phase resolved optical emission spectroscopy (PROES). The DF excitation results in a time-varying electric field which is determined by the total LF and RF gas voltage and the spatial ion distribution which only responds to the LF component. By tuning the amplitude ratio of the superimposed LF and RF signals, the effect of each frequency component on the DF discharge mechanism was analysed. The LF excitation results in a transient plasma with the formation of an electrode sheath and therefore a pronounced excitation near the substrate. The RF oscillation allows the electron trapping in the gas gap and helps to improve the plasma uniformity by contributing to the pre-ionization and by controlling the discharge development. The possibility of temporally modifying the electric field and thus the plasma generation mechanism in the DF discharge exhibits potential applications in plasma-assisted surface processing and plasma-assisted gas phase chemical conversion.
Highlights
Development of a large linear or volumetric source of diffuse non-thermal plasma at atmospheric pressure remains to be an essential challenge both from a scientific and a technological point of view
The excitation dynamics and the plasma generation mechanism were studied by means of electrical characterization and phase resolved optical emission spectroscopy (PROES)
The DF excitation results in a time-varying electric field which is determined by the total low frequency (LF) and radio frequency (RF) gas voltage and the spatial ion distribution which only responds to the LF component
Summary
Development of a large linear or volumetric source of diffuse non-thermal plasma at atmospheric pressure remains to be an essential challenge both from a scientific and a technological point of view. It was demonstrated that application of such a diffuse discharge as a plasma source for the roll-to-roll AP-PECVD process in conjunction with organosilicon precursors results in high quality inorganic silica-like thin films, which can be deposited on thermally sensitive polymeric substrates [14,15,16] In this process, the increased discharge power density allows the synthesis of silica-like films with improved microstructure, lower impurities level and excellent gas diffusion barrier properties [16, 17]. PROES is sensitive to the dynamics of high energetic electrons (E ⩾11.7 eV) and yields information on the plasma parameters with high temporal and spatial resolution [37] In this study, it was demonstrated for the first time that the dual frequency (200 kHz + 1 3.56 MHz) excitation can produce homogeneous, filament-free DBDs at atmospheric pres sure in Ar/O2 gas mixture.
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