Molecular-scale investigation of C₆₀/p-sexiphenyl organic heterojunction interface

In situ low-temperature scanning tunneling microscopy (LT-STM) and ultraviolet photoelectron spectroscopy (UPS) experiments have been carried out to investigate the interface properties at the C₆₀/p-sexiphenyl (6P) organic–organic heterojunction interface, including the interfacial energy level alignment and the supramolecular packing structures. As revealed by UPS measurements, the vacuum level is almost aligned at the C₆₀/6P interface, suggesting that the interface is dominated by weak intermolecular interactions, such as van der Waals and π–π interactions. In situ LT-STM experiments also indicate the formation of a molecularly sharp C₆₀/6P interface with hexagonally-close-packed C₆₀ layers nucleated atop 6P layer on graphite.