Photocurrents and thermally stimulated currents in epoxy resin: effects of mechanical stress

Photocurrent and thermally stimulated current (TSC) measurements were carried out on epoxy resin films with and without mechanical stress. Considerable photoconduction was observed, which the authors interpret as indicating the importance of electronic conduction in epoxy resin. Both photocurrent and TSC samples under mechanical stress showed dependence on the polarity of the applied field, which was not seen in samples without mechanical stress. Under mechanical stress, the photocurrent under a positive bias (i.e. positive voltage being applied to the illuminated electrode) was larger than that under negative bias and the TSC from a photoelectric formed under positive bias was also larger than for a negative bias. This led to the conclusion that the defects caused by the mechanical stress act as hopping centers for holes at low temperatures enhancing hole transport. The defects also act as trapping centers and lead to a TSC peak P₂≃247 K where the defects are diminished by stress relaxation. At high temperatures where the defect levels are ineffective, the hole conduction is almost equal to the electron conduction samples free of mechanical stress