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.

Keywords:

• Thermally stimulated depolarization current
• High-energy ion irradiation
• Dielectric relaxation
• Kapton-H polyimide

Acknowledgements

Funds were provided by Defense Research and Development Organization, Government of India and Nuclear Science Center, New Delhi. The authors are thankful to Dr. D. K. Avasthi (scientist, NSC, New Delhi) for his help in irradiation of the samples and Dr. Maneesha and Mr. Sridharbabu (Department of Applied Physics, National Institute of Technology, Kurukshetra) for their help in the preparation of manuscript.