Binding and ordering of C60 on Pd(110): Investigations at the local and mesoscopic scale

Abstract

We present a comprehensive study on the binding and ordering of C60 on a Pd(110) surface employing scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD). Three well-ordered structures evolving at elevated temperatures were identified, with (∓2 ±5 7 −1), (4×5), (4×8) unit cells and a coverage of 1, 0.82 and 0.77 physical monolayers, respectively. The rearrangement of Pd substrate atoms turns out to play a crucial role in the evolution of thin C60 films. In STM images alternating bright and dark molecular rows are found for the regular structures. This height difference is attributed to a restructuring of the Pd substrate. Whereas the C60 molecules of the bright molecular rows are embedded in one layer deep microscopic pits, C60 accommodated in two layer deep pits account for the dark molecular rows. XPD results complete the understanding of the film structure. They reveal that the orientation of the C60 cages is unique in the regular structures; the molecules are facing with a 5–6 bond towards the substrate.