Electret behaviour of ion irradiated polycarbonate and kapton-H polyimide films

Abstract

The electret state of a polymer arises from the induced polarization owing to the frozen in phenomenon of electric charges. The study of electret nature using thermally stimulated discharge current (TSDC) technique reveals the nature of various relaxation processes in a polymer. When a polymer is irradiated with high energy ions their dielectric relaxations get affected which can be investigated using above mentioned technique. Reported here are the results of TSD current spectra of films of polycarbonate (PC) (irradiated with 100 MeV Ag +, flux; 1 × 10 11 and 1 × 10 9 ions/cm 2) and kapton-H polyimide (irradiated with 100 MeV O ++, flux; 1 × 10 5 ions/cm 2). The as-received and irradiated samples of PC were polarised at 120 °C using a 200 kV/cm electric field while those of kapton-H were polarised at 90 °C, field; 133 kV/cm and 180 °C, field; 266 kV/cm. With PC it is observed that the irradiation does not affect the location of TSDC peak occurring at 144 °C (activation energy; 0.6 eV); however, the peak magnitude changes with irradiation dose. The peak being associated with dipolar relaxation the ion-irradiation seems to have changed the number of dipoles. The high temperature TSDC spectra is however largely affected by irradiation giving evidence of the presence of new traps. With kapton-H, it is observed that TSD current changes its direction (anomalous TSDC) in irradiated samples in the high temperature region. Such behaviour has not been observed in the thermoelectrets of as-received samples. Only the corona charged electrets were observed to give such anomalous TSDC behaviour. This suggests the creation of new energy traps from irradiation. The bulk nature of this relaxation is confirmed by the TSDC of repoled samples. The irradiation induced shallow energy traps along with dipolar relaxation are also observed from the TSDC spectra in the low temperature region.