AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP5
The Impact of Molecular Properties on the Geometric Structure of Self Assembled Monolayers of Arenethiols on Cu(111)

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: X. Lin, University of California at Riverside
Authors: X. Lin, University of California at Riverside
K.-Y. Kwon, University of California at Riverside
K.L. Wong, University of California at Riverside
L. Bartels, University of California at Riverside
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Self assembled monolayers (SAMs) of organic molecules on metal surfaces are the subject of great interest due to their utility in nanodevices. The structure of individual SAMs is not only determined by the binding of their constituents to the substrate but also by intermolecular interactions. One challenging problem is to understand how molecule-molecule interactions affect the structure of the monolayer. We explored the impact of these interactions using thiolphenol (TP) molecules on Cu(111) as a model system for aromatic thiol SAMs. Molecular properties can be changed in a systematic fashion by selective substitutions. We have performed STM studies of monolayers of thiolphenol (TP) molecules and several halogen substituted para- and meta-X-TP derivates (where X is Br, Cl or F). For both meta and para substituted molecules we find that the complexity of the monolayers increases with the electronegativity of the substituent, which suggests that electrostatic interactions of the molecular dipole and quadrupole moment play a critical role in determining the film structure. Penta-fluoro-substituted TPs exhibit no ordering at all, while unsubstituted TPs exhibit no long range order, yet are able to form stable aggregates up to seven molecules. Despite the fact that all the studied molecules share the common feature of having a thiol group as linker to the metal substrate, they display a vast diversity in their aggregation behavior as well as in their monolayer structures. This demonstrates the utility of this model system where the molecule-molecule interaction can be finely tuned to exhibit the full spectrum of aggregation behavior, from no ordering via clustering to formation of layers with complex patterns.