Degradation of polyimide under irradiation with swift heavy ions

Stacks of polyimide foils were irradiated with different swift heavy ions (Ti, Mo, Au) of 11.1 MeV/nucleon energy and fluences between 1 × 1010 and 2 × 1012 ions/cm2. Beam-induced degradation of the imide group was analyzed by Fourier-transform infrared spectroscopy studying the absorption band at 725 cm−1 as a function of dose. In the UV-Vis spectral range, the absorption edge is shifted to larger wavelengths indicating carbonization. Such modifications are linked to the deposition of a critical dose of 2.7 MGy (Ti) and 1 MGy (Mo, Au). In addition, irradiation-induced changes of the electrical conductivity were studied by means of dielectric spectroscopy.