  The contrast obtained in scanning tunneling microscopy (STM) and atomic force
microscopy (AFM) images is determined by the tip termination and symmetry.
Functionalizing the tip with a single metal atom, CO molecule or organic
species has been shown to provide high spatial resolution and insights into
tip-surface interactions. A topic where this concept is utilized is the
adsorption of organic molecules at surfaces. With this work we aim to
contribute to the growing database of organic molecules that allow assignment
by intra-molecular imaging. We investigated the organic molecule
para-sexiphenyl (C36H26, 6P) on Cu(100) using low-temperature STM and
non-contact AFM with intra-molecular resolution. In the sub-monolayer regime we
find a planar and flat adsorption with the 6P molecules rotated 10{\deg} off
the <010> directions. In this configuration, four of the six phenyl rings
occupy almost equivalent sites on the surface. The 6P molecules are further
investigated with CO- functionalized tips, in comparison to a single-atom metal
and 6P-terminated tip. We also show that the procedure of using adsorbed CO to
characterize tips introduced by Hofmann et al. Phys. Rev. B 112 (2014) 066101
is useful when the tip is terminated with an organic molecule.

Materials Science