Influence of storage conditions on the electronic structure of Au and interfacial state formation with C60

초록

As surface electronic structures are highly sensitive to environmental factors, the electrode storage conditions significantly influence the interfacial energy-level alignment. In this study, we investigated the effect of ultrahigh vacuum (UHV) storage on the surface electronic properties of Au and examined the influence of surface contamination on the energy-level alignment with C-60 using in situ ultraviolet and X-ray photoelectron spectroscopy. The work function (WF) of clean Au decreased from 5.08 to 4.48 eV owing to the pushback effect caused by surface contaminants. In contrast, air-exposed Au with initially higher contamination levels exhibited a WF of 4.37 eV with minimal variation over time. Despite the notably lower WF of UHV-stored Au compared with that of clean Au, the highest occupied molecular orbital (HOMO) position of C-60 remained constant because of the Fermi-level pinning caused by the high density of interfacial states. However, air-exposed Au displayed fewer interfacial states owing to a passivating effect from heavy contamination, resulting in a downward shift in the HOMO level. These results provide valuable insights into the electronic structure of the electrode surfaces and their interfacial energy-level alignment, which is an important factor in optimizing high-efficiency organic electronic devices.

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