Determination of Band Alignment at Au/PTFE and Au/PP Interfaces by First-Principles Calculations and XPS

Since charge injection from metals into insulating polymers leads to electrical degradation and failure of various electrical devices, it is essential to clarify the band alignment at the metal/insulating polymer interface. However, the electronic structure at the metal/insulating polymer interface has not been studied experimentally. In this contribution, band alignments at the Au/polytetrafluoroethylene (PTFE) and Au/polypropylene (PP) interfaces were determined by first-principles calculations using density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) measurements. The calculated electronic properties on the Au/PP interface are in agreement with the experimental results, indicating that the vacuum level shift at the interface is slight (below 0.3 eV). On the other hand, in the case of PTFE, even though the computed vacuum level shift for an ideal interface was small (-0.1 eV), the experimental results indicated that the vacuum level shift can be more than 1.7 eV. The results suggest that, in actual systems, the vacuum level shift may be caused by the impurities or defects at the interface. Our work has led us to conclude that the band alignment of the metal/polymer interface depends not only on the combination of material species but also on the way the contact is formed between them.