Interfacial Phenomena in Polymer Films and Generation of Maxwell Displacement Current

摘要

Interfacial electrostatic phenomena in ultrathin polyimide films have been examined, and the space charge distribution and electronic density of states have been determined. The presence of excess negative charges at the film-metal interface of nanometer thickness has been revealed and the alignment of the surface Fermi level of polymer films and Fermi level of metals have been elucidated. Taking into account the interfacial space charge, a step structure observed in the Ⅰ-Ⅴ characteristic of metal-polyimide-rhodamine-polyimide-metal junction, very similar to Coulomb staircase, is well explained. Furthermore, the electrical breakdown mechanism of a nanometer-thick polyimide film is found quite different from that of micrometer-thick films, owing to the presence of this interfacial nanometric space charge. Finally, for a profound understanding of the behaviour of surface monolayer, the Maxwell displacement current measurement coupled with optical second harmonic generation measurement has been employed.