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 C-60/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 C-60/6P interface, suggesting that the interface is dominated by weak intermolecular interactions, such as van der Waals and pi-pi interactions. In situ LT-STM experiments also indicate the formation of a molecularly sharp C-60/6P interface with hexagonally-close-packed C-60 layers nucleated atop 6P layer on graphite. (C) 2011 American Institute of Physics. [doi:10.1063/1.3582789]