Thermally stimulated spontaneous current investigations in 75 MeV oxygen-ion-irradiated kapton-H polyimide

Thermally stimulated spontaneous currents in 75 MeV oxygen-ion-irradiated kapton-H polyimide samples sandwiched between similar (M-P-M) and dissimilar (M-1-P-M-2) electrodes in the temperature range of 20-250 degrees C have been studied. Metals used as electrodes in the present investigations are having different work functions (Bi: 4.22, Al: 4.28, Cr: 4.37, Cu: 4.70 and Au: 5.1 eV). One maxima in the temperature region 30-60 degrees C and other in the temperature region 100-120 degrees C have been observed, termed as gamma and beta relaxations, respectively. gamma-Relaxation is associated with the water absorption and beta-relaxation is associated with the presence of dipoles in the material. The magnitude of the current depends on the type of electrode combinations used: either similar (M-P-M) or dissimilar (M-1-P-M-2) electrode systems. The value of current in M-1-P-M-2 combinations is more in comparison with M-P-M systems, as the internal potential difference developed in dissimilar electrodes is more as compared with the similar electrode system. The carbonyl groups present in the structure of kapton-H polyimide are the most affected group, due to the contact electrode system and ion irradiation. Aluminum atoms interact with imide carbonyl groups in kapton-H polyimide form carbonyl (>CO)-metal complex. As a result of ion irradiation, demerization of carbonyl groups and formation of some new polar-subpolar groups take place. The moisture in ion-irradiated samples promotes the current magnitude via helping in transport or conduction of charge carriers through polyimide.