Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge.

A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N₂/O₂ gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm^-1 to unravel the plasma-polymer interactions. The absorption features of H_xN_yO_z, CO_x, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high CO_x production. The presence of HCOOH in the gas effluent, formed through plasmachemical synthesis of CO_x, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the CO_x production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the CO_x production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the CO_x production is dominated by polymer etching. [ABSTRACT FROM AUTHOR]