Electrostatic phenomena at film/film interface in polyimide Langmuir-Blodgett films

Surface potential built at the interface between two kinds of heat-treated polyimide Langmuir-Blodgett (LB) films (denoted as PI and TRIPI) was measured in a box shielded from light while nitrogen gas was flowing through the box. The surface potential depended on the number of deposited layers, and the surface potential saturated when there are several deposited layers. The polarity of the potential across the PI/TRIPI LB film interface suggests that excess charges (electron) were transferred from TRIPI into PI. It was found that space charges were distributed in both PI and TRIPI LB films within the range of several nanometers from the PI/TRIPI interface. Surface potential of PI deposited on semiconducting materials used in power cable engineering was also examined. The potential depended on the semiconducting material and on the number of deposited layers of PI. The difference in the saturated potential across PI and semiconducting material coincided well with the difference in the fermi level of these materials, indicating that excess charges were transferred until thermodynamic equilibrium was established at the interface between PI and the semiconducting materials. The electric field of the order of 10(8) V/m was formed at the interface.