Temperature dependence of electrostatic phenomena at the electrode-polyimide LB film interface before and after photoirradiation

Abstract

Surface potentials of two kinds of heat-treated polyimide (PI and TRIPI) Langmuir-Blodgett (LB) films deposited onto Au, Cr, Al and ITO electrodes were measured in a dark vacuum vessel at various temperatures before and after photoirradiation. The surface potential value comes to a saturation when the number of deposited layers reaches several tens. The saturated surface potential value shows a linear dependence on the work function of electrodes at temperatures between −100 °C and 150 °C before photoirradiation and at room temperature after photoirradiation. It was suggested that the excessive charges were transferred from electrodes into PILB films until thermodynamic equilibrium was established at the interface. The surface potential change of PI is negative, while that of TRIPI is positive under the increase of temperature. Contrary to that, the surface potential change of PI is positive and that of TRIPI is negative after photoirradiation. The excessive charge of very high density exists at the metal-PI interface and its density increases with the increase of temperature.