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

We present a comprehensive study on the binding and ordering of C-60 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)), (4x5), (4x8) 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 C-60 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 C-60 molecules of the bright molecular rows are embedded in one layer deep microscopic pits, C-60 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 C-60 cages is unique in the regular structures; the molecules are facing with a 5-6 bond towards the substrate. (C) 2001 American Institute of Physics.