The characteristics of a low frequency (70 kHz) discharge with non-symmetrical
configuration of electrodes in He–O2 mixtures were investigated. The Langmuir probe technique,
emission spectroscopy, mass spectrometry and absorption spectroscopy were used for plasma
diagnostics. The physicochemical properties 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 energetic character of the
discharge. The very efficient loss of He excited species and in particularly the metastables, for
amounts of O2 higher than a few percents, affects the surface modification in terms of
crosslinking, and therefore the stability. This work has shown that one of the important species
responsible for the crosslinking process leading to stable surface properties could be the helium
metastables.