Thermally stimulated depolarization current behaviour of 75 MeV oxygen ion irradiated Kapton-H polyimide film

Abstract

The thermally stimulated depolarization current (TSDC) technique has been used to investigate the various dielectric relaxation processes in high-energy ion irradiated Kapton-H polyimide. The 25 μm thick Kapton-H samples were irradiated with 75 MeV oxygen ions (fluences: 1.88×1011, 1.88×1012, 1.88×1013, 5.63×1012 ions/cm2) at the Nuclear Science Center (Pelletron Facility), New Delhi. The TSDC characteristics were obtained at a linear heating rate of 2 °C/min for different poling temperatures varying from 80 to 250 °C and poling fields from 160 to 400 kV/cm. The TSDC spectra mainly consist of four current maxima, viz. γ, β, α and ρ in the increasing order of temperature. The γ-relaxation has been attributed to the increased water absorptivity in Kapton-H due to irradiation. The demerization of carbonyl groups, cross-linking of imide groups and formation of free radicals due to energetic heavy ion irradiation in Kapton-H polyimide have been held responsible to govern the behaviour of β, α and ρ relaxations. In the vicinity of the β-relaxation, a new relaxation process, termed as δ-relaxation, is also observed. The activation energy values (0.78, 0.60, 1.04 and 1.32 eV for γ, β, α and ρ relaxations, respectively) for different relaxations were calculated by the Bucci plot method.