Study of plasmas in He-O-2 mixtures and their role on the stability of thesurface properties of polymers

The characteristics of a low frequency (70 kHz) discharge With non-symmetri cal configuration of electrodes in He-O-2 mixtures were investigated. The L angmuir probe technique, emission spectroscopy, mass spectrometry and absor ption spectroscopy were used for plasma diagnostics. The physicochemical pr operties of PET (polyethylene terephtalate) were analyzed via contact angle measurements and XPS spectroscopy. The presence of the oxygen is shown to modify both the densities of the helium metastable states and also the ener getic character of the discharge. The very efficient loss of He excited spe cies and in particularly the metastables, for amounts of O-2 higher than a few percents, affects the surface modification in terms of crosslinking, an d therefore the stability. This work has shown that one of the important sp ecies responsible for the crosslinking process leading to stable surface pr operties Could be the helium metastables.