Charge Injection Barriers at the Au/Polypropylene and Au/Polyimide Interfaces: The Effect of Polymer Polarity

Degradation and breakdown of dielectric polymers are attributed to the process of charge injection from a metal into the dielectric polymer. The charge injection barrier at the interface between the metal and dielectric, which is associated with the band alignment, is regarded as a crucial factor influencing the process of charge injection. In this study, the interfaces between the Au electrode and the polymer were investigated at the atomic level with a combination of X-ray photoelectron spectroscopy measurements and first-principles calculations in order to reveal the mechanism determining the band alignment. We investigated the Au/polypropylene (PP) and Au/polyimide (PI) interfaces. PP and PI were chosen as examples of polymers commonly used as insulating materials, with PP being non-polar and PI being polar. The results indicate that the alignment of vacuum levels between the metal and polymer is a critical determinant of the band alignment at the interface, irrespective of the polarity of the polymers.