Electrical current measurements on polystyrene films

Currents decaying with time according to a 1/ t law were observed in polystyrene films when a direct voltage was applied. Upon voltage removal, discharge currents were recorded, equal in magnitude to the charge currents. The currents were strongly dependent on the texture of the edges of the evaporated gold electrodes. Study of the currents as a function of several parameters (voltage, electrode size, electrode shape and film thickness) leads to the conclusion that previous proposals about the origin of transient currents in similar insulating films are not applicable to the present case. It is shown that the carrier currents are confined to flow on the surfaces of the film. Moreover, if the surface resistivity is assumed to grow exponentially with the distance from the electrode edge, the predicted current agrees well with the experimental results.