Photocurrents and thermally stimulated currents in epoxy resin composites

The authors prepared epoxy-alumina two-layer composite films as models of a polymer-filler interface and studied the effect of interfaces on electronic conduction by measuring photocurrents and thermally stimulated currents (TSC). It is shown that, at high fields and low temperatures, holes are more mobile than electrons in epoxy-alumina composites, independent of mechanical stress. Most of the holes in the epoxy layer can pass through the epoxy-alumina interface and move in the alumina bulk, increasing the conduction current in the alumina by about two orders of magnitude. This interfacial phenomenon cannot be explained by the conventional Maxwell-Wagner model. TSC measurements on the composite showed that some of the holes were trapped at the epoxy-alumina interface, in the alumina bulk or the epoxy bulk near the interface, and gave rise to new TSC peaks. At high fields and room temperature, the photoconduction is governed by the alumina layer and is well explained by Maxwell-Wagner model. The dark current in the composite is governed by the epoxy layer