Jan 28, 2009
Creating molecular nano-structures
The bottom-up fabrication of molecular nano-structures constitutes a very promising strategy for creating future functional devices in fields such as molecular electronics and materials science. Reliable molecular applications will, however, require precise control of both, molecular structure formation and structural perfection. Within this scope, molecular self-assembly has proven to be a versatile method for fabricating well-ordered molecular structures.
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.
About the author
Felix Loske has carried out this study in the group of Dr. Angelika Kühnle at the University of Osnabrück (Germany) as part of his PhD thesis in the field of molecular self-assembly. Others who have contributed to this work are Ralf Bechstein, Jens Schütte, Dr. Frank Ostendorf and Prof. Michael Reichling, all from the University of Osnabrück. This work has been supported by the German Research Foundation (DFG) through the Emmy Noether-programme and the integrated project PicoInside of the European Union.