Energy Level Alignment at the Fullerene/Titanium Oxide Ultrathin Film Interface

The performance of molecule based electronic devices can be improved by use of transition metal oxides (TMO) as charge injection buffer layers between electrodes and organic semiconductors. It is known that the appropriate energy level alignment at the molecule/TMO interface determines the efficiency of the respective TMO. Herein, scanning tunneling microscopy is employed to characterize the interface formed by fullerenes (C60) deposited on a titanium oxide (TiO) ultrathin film, which is created by oxidation of a Pt3Ti(111) surface. Individual C60 are identified with orbital resolution, and the interfacial and intermolecular interactions are characterized in detail. Furthermore, the energy level alignment at the C60/TiO ultrathin film interface is deduced based on scanning tunneling spectroscopy data. The results demonstrate that the C60/TiO interface corresponds to a type-I heterojunction and, thus, is useful to decouple C60 molecules from the metallic alloy surface.