Study of late argon-nitrogen post-discharge interactions with oxidized iron surfaces

Nitrogen-containing post-discharges are widely used for enhancement of poly mer printability and adhesion and wettability properties. It has also appli cations in the field of remote plasma enhanced chemical vapour deposition o f thin nitride films or nitriding. Interactions occurring between an argon- N-2 post-discharge and oxidized iron surfaces are studied. Measurements are based on optical emission spectroscopy measurements. Two regimes are consi dered. First, the analysis of transient effects sheds light on the cleaning effects which modify permanently the topmost surface of oxidized iron subs trates. They are evidenced by XPS measurements. Two steps occur. During the first one, a reaction between nitrogen atoms and carbon of ketones or carb onyl-like groups probably due to acetone residue, identified by XPS analyse s, gives CN radicals. The CN(B(2)Sigma,v) --> CN(X(2)Sigma,v') transition i s identified by optical emission spectroscopy. This emission vanishes progr essively as carbon is consumed and the second step starts at the end of the violet emission where the loss probability gamma(N) of nitrogen atoms incr eases, The increase of the recombination rate is attributed to abstraction reactions of adsorbed elements by nitrogen atoms to form nonemissive specie s. For example, hydroxide groups are removed by the post-discharge. The sur face modifications induced by this treatment are reproducible. This was ver ified by comparison between the behaviours of the native oxide and a 0.5-mu m-thick layer grown by controlled post-discharge oxidation, When the stead y-state regime is reached, the loss probability gamma(N) on the treated sur faces is determined in a range of temperatures (i.e., 300-473 K) where the nitrogen bulk-diffusion is assumed to be negligible, Nitrogen atoms recombi ne according to an Eley-Rideal mechanism and gamma(N) = (8.2 +/- 0.5) x 10( -2) exp(-11400 +/- 500/RT). (C) 2000 Elsevier Science B.V. All rights reser ved.