Understanding of the subtle balance between intermolecular and molecule-substrate interactions allows for tailoring molecular structure formation. Both interactions are decisive for the molecular equilibrium structure.

Researchers at the University of Osnabrück (Germany) have investigated the structure formation of C60 "bucky balls" - the molecular analogue to a soccer ball - on the rutile TiO2(110) surface, where molecule-substrate and intermolecular interactions are in about the same range. C60 molecules on dielectric surfaces are of great interest due to promising future applications in (opto)electronic devices such as organic solar cells. The dielectric TiO2 surface represents a prototypical transition metal oxide. For this study, non-contact atomic force microscopy (NC-AFM) was employed under ultra-high vacuum conditions (UHV), allowing for high-resolution imaging on insulating substrates at the atomic level.

The C60 molecules were found to arrange in a centered rectangular superstructure, templated by the protruding surface bridging oxygen rows. Although the TiO2 surface is known to exhibit a high density of intrinsic defects, the regular and compact shaped C60 islands were of striking perfection. This "self-healing" effect might constitute a decisive advantage of the studied system for future applications. In addition, uni-directional molecular strands were observed to run in two distinct directions, originating from anti-phase domain boundaries caused by stacking faults.

Molecular self-assembly is believed to be one of the few viable strategies for overcoming the miniaturization limitation of classical lithography. The present example demonstrates prospects of molecular self-assembly on dielectric substrates.