ROLE OF ELECTRONIC PARTICLE SURFACE INTERACTIONS DURING THE SPUTTER DEGRADATION OF POLYMERS

Rates of damage for polymer surfaces subjected to sputtering may be evaluated by observing the time dependence of fragment ion signal intensities, provided due care is taken to exclude effects due to sample charging. The fragment ion signal time dependence has been investigated in detail for two polymers, poly(ethylene terephthalate) (PET) and poly(tetrafluoroethylene) (PTFE). Charged and neutral primary particles have been compared, and the effects of primary particle mass have also been estimated. In general, for PET the decay rates were much faster for bombardment with charged particles, indicating that electronic interactions between the surface and the bombarding particle were an important contribution to sample degradation. For the heavier xenon ions, however, mass effects were relatively more important. For PTFE, the difference between damage rates for charged and neutral species was greater still. It was observed that at low doses, much of the time-dependent behavior could be eliminated by the use of neutral primary particles.