Energetics of reactions in a dielectric barrier discharge with argon carrier gas: Halocarbons

The novel method we developed for understanding energy exchanges between argon (Ar) carrier gas and precursor molecules in a large-area $216\, cm^2$ dielectric barrier discharge (DBD) reactor has resulted in a series of articles, each relating to a different family of organic compounds. This communication focuses on two new groups, perfluorocarbons, $C_xF_y$ and perchlorocarbons, $C_xCl_y$, and compares results with earlier ones for hydrocarbons, $C_xH_y$[1] and hydrofluoromethanes, $CH_xF_y$[2]. The precursors (in $^o/_{oo}$ concentrations) were mixed with Ar in a 20 kHz, 8 kV (peak to peak) DBD. For each separate compound $E_m$, the energy (in eV) absorbed per molecule, was determined from measurements of the time resolved discharge current, $I_d$, and the gap voltage, $V_{gap}$. Optical emission spectra were recorded and $E_m$ was plotted as a function of precursor flow rate, $F_d$. The process generally led to thin “plasma polymer” (PP) deposits (e.g. on Si wafer substrates). Their characteristics, like their C/F or C/Cl composition ratios from XPS measurements, strongly correlated with $E_m$ and $F_d$, as did PP deposition rates and water contact angles. [1] B. Nisol et al., Plasma Process Polym, 2016;14:e201600191 [2] S. Watson et al., Plasma Process Polym, 2020;17:e201900125.