Swift heavy ion induced modification in polyimide films

Polyimide (PI) films were irradiated by 80 MeV O6+ ions at different fluences of 8.5 × 1012 ions/cm2, 1.5 × 1013 ions/cm2 and 2.5 × 1013 ions/cm2. The modified films were characterized by microhardness tester, LCR meter, FTIR spectroscopy and thermogravimetric analysis (TGA). It is observed that the hardness of the films increases as fluence increases. This may be attributed to the cross-linking effects as corroborated with FTIR spectra. A plot of conductivity versus log frequency displays a sharp increase in conductivity at a frequency of 20 kHz, and the effect of irradiation is significant at higher fluences. The dielectric constant/loss is observed to change with the fluence. TGA thermograms indicate that the composition of the sample degrades progressively during irradiation due to the emission of hydrogen gas and/or other volatile gases. It suggests that ion beam irradiation converts the polymeric structure into a hydrogen depleted carbon network, which makes the polymer harder and more conductive.