Thermally stimulated spontaneous currents from Kapton polyimide–metal contacts

The spontaneous current emission (SCE) in Kapton-H. polyimide films sandwiched between similar and dissimilar electrodes is investigated in the temperature range 313 to 533 K. The magnitude and direction of the current (Is) are found to depend on the choice and combination of the electrode materials. But for a particular pair of clectrodes, the direction of current remains unchanged during heating and cooling. The magnitude of Is from metal1–Kapton–metal2 (M1–K–M2) systems comes out to be nearly ten times higher than from the M–K–M systems. The thermal current spectra for M1–K–M2 systems consist of two peaks around 410 K (P1) and 473 K (P2), while for M–K–M cases a single peak (P1) is observed. The peak position varies with heating rate. The relative current suppression during repeated heatings depends on the time interval between the start of that particular heating and the end of preceding cooling. As a result of doping the sample with iodine, the current magnitude is enhanced. The spontaneous current from Kapton is attributed to origins like contact electrification, electrochemical mechanisms at metal–polymer interfaces, disorientation of dipoles, and space charge motion.