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

Abstract

Thermally stimulated spontaneous currents in 75 MeV oxygen-ion-irradiated kapton-H polyimide samples sandwiched between similar (M–P–M) and dissimilar (M1–P–M2) electrodes in the temperature range of 20–250°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°C and other in the temperature region 100–120°C have been observed, termed as γ and β relaxations, respectively. γ-Relaxation is associated with the water absorption and β-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 (M1–P–M2) electrode systems. The value of current in M1–P–M2 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 (>C═O)-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.