Role of active species in surface cleaning by an Ar-N2 atmospheric pressure post-discharge

Post-discharge cleaning at atmospheric pressure of oxidized iron foils rinsed by acetone and methanol is studied by XPS. The influence of the temperature (T < 450 K) and the UV photons on cleaning is negligible. When pure rare gases (He, Ne, Ar) are used, metastable species in post-discharge are transported downstream the plasma and relax their energy on the surface. C-C bonds are mainly removed by this process. When nitrogen is added to the rare gas (from 0 to 4.6 vol.%), a selective influence on the etching process of the surface contaminants by nitrogen atoms is observed. The removal kinetics of chemical groups analysed by XPS is determined by using an exponential decay function corresponding to a first-order abstraction process. The decrease of C(1s) in N-C, O(1s) in N-C-O and N(1s) XPS peaks is correlated with the nitrogen atom concentration in the carrier gas. Reactions between nitrogen atoms and specific carbon containing groups occur (probably C-OH bonds of methanol). Stronger bonds like C=O (probably from acetone) are not removed by the post-discharge.