Ammonia Plasma Treatment of PTFE Under Known Plasma Conditions

Ammonia plasmas produced in a helical resonator have been investigated using an energy-selective mass spectrometer and an r.f.-compensated Langmuir probe. The effect of processing parameters on the plasma composition and ion energy distributions have been examined. The dominant ion present in the plasma was found to be NH4+, which varied in concentration between 95% and 65%, dependent upon operating conditions. Similarly, by relatively small variations in processing parameters it was possible to vary the NH3+ ion concentration between 1.7 and 31%. In addition, no radicals (NH2•, NH• or N•) were detected using threshold ionization mass spectroscopy. Polytetrafluoroethylene (PTFE) samples were treated under a variety of different plasma conditions, and the chemical changes induced were studied by in situ XPS. Defluorination was observed to be greater under conditions that yield low ion energies or high concentrations of NH3+ ions. Conditions giving rise to significant concentrations of NH3+ ions result in the production of NH3+F- groups. Evidence is provided suggesting that NH3+ ions are much more reactive with PTFE surfaces than NH4+ ions.