ELECTRET BEHAVIOR OF ION-IRRADIATED POLYCARBONATE AND KAPTON-H POLYIMIDE FILMS

The electret state of a polymer arises from the induced polarization o wing to the frozen in phenomenon of electric charges. The study of ele ctret nature-using thermally stimulated discharge current (TSDC) techn ique reveals the nature of various relaxation processes in a polymer. When a polymer is irradiated with high energy ions their dielectric re laxations get affected which can be investigated using above mentioned technique. Reported here are the results of TSD current spectra of fi lms of polycarbonate (PC) (irradiated with 100 MeV Ag+, flux; 1 x 10(1 1) and 1 x 10(9) ions/cm(2))and kapton-H polyimide (irradiated with 10 0 MeV O++ flux; 1 x 10(5) ions/cm(2)). The as-received and irradiated samples of PC were polarised at 120 degrees C using a 200 kV/cm electr ic field while those of kapton-H were polarised at 90 degrees C, field ; 133 kV/cm and 180 degrees C, field; 266 kV/cm. With PC it is observe d that the irradiation does not affect the location of TSDC peak occur ring at 144 degrees C (activation energy; 0.6 eV) however, the peak ma gnitude changes with irradiation dose. The peak being associated with dipolar relaxation the ion-irradiation seems to have changed the numbe r of dipoles. The high temperature TSDC spectra is however largely aff ected by irradiation giving evidence of the presence of new traps. Wit h kapton-H, it is observed that TSD current changes ifs direction (ano malous TSDC) in irradiated samples in the high temperature region. Suc h behaviour has not been observed in the thermoelectrets of as-receive d samples. Only the corona charged electrets were observed to give suc h anomalous TSDC behaviour. This suggests the creation of new energy t raps from irradiation. The bulk nature of this relaxation is confirmed by the TSDC of repoled samples. The irradiation induced shallow energ y traps along with dipolar relaxation are also observed from the TSDC spectra in the low temperature region. (C) 1998 Elsevier Science. All rights reserved.