Formation of energetic heavy ion tracks in polyimide thin films

• Ion tracks formed in polyimide via irradiation with high energy heavy ions.
• Complementary techniques track the changes in composition of polyimide during irradiation.
• Ion beam analysis aids the identification of signals from residual gas analysis.
• A multi-step process of polyimide modification is observed and modelled.
• The multi-step process is related to ion track density and overlap.

Polyimide thin films have been irradiated with a high energy beam of heavy ions to a fluence of approximately 4 × 1013 ions/cm2. Proton backscattering spectroscopy was used to measure the composition of the films, which showed that oxygen was the element that exhibited the most rapid loss from the film. The gases evolved from the film during polymer modification were monitored using a quadrupole mass spectrometer for residual gas analysis (RGA). The fluence dependence of RGA signals were indicative of multi-step processes of gas release, whereby the passage of an ion through a region of pristine film changes the local molecular structure to one that will more readily form volatile species when subsequent ions pass.