Electronic structures of 1-ML C84/Ag(111): Energy level alignment and work function variation

The electronic structures of fullerene/metal interface are critical to the performance of devices based on fullerene in molecular electronics and organic electronics. Herein, we investigate the electronic structures at the interface between C-84 and Ag(111) by photoelectron spectroscopy and soft X-ray absorption spectroscopy techniques. It is observed that C-84 monolayer on Ag(111) surface (1-ML C-84/Ag(111)) has metallic nature. A charge transfer from substrate to the unoccupied states of C-84 is determined to be 1.3 electrons per molecule. However, the work function of 1-ML C-84 (4.72 eV) is observed slightly larger than that of the clean Ag(111) substrate (4.50 eV). A bidirectional charge transfer model is introduced to understand the work function variation of the fullerene/metal system. In addition to the charge transfer from substrate to the adsorbate's unoccupied states, there exists non-negligible back charge transfer from fullerene occupied molecular orbital to the metal substrate through interfacial hybridization. The Fermi level will be pinned at similar to 4.72 eV for C-84 monolayer on coinage metal substrate. (C) 2017 Elsevier B.V. All rights reserved.