Tuesday, 24 May 2005 - 3:05 PM

This presentation is part of: Surface and Interface Science II

Structure in Self-Assembled Organic Thin Films: Chirality, Nano-patterns, and Interaction Energies

Steven L. Bernasek1, Feng Tao1, and Yuguang Cai2. (1) Princeton University, Princeton, NJ, (2) Brookhaven National Laboratory, Upton, NY

Physisorption of substituted alkanes at the basal plane of graphite results in a wide range of self-assembled monolayer structures. Many of these structures exhibit chirality in two dimensions and patterns on the nanometer length scale. The formation and stability of these structures can be used to probe the interaction energies that control self-assembly. The structures discussed include a chiral monolayer formed when octadecanol is distorted into a chiral overlayer upon adsorption. Chiral pairing has been observed in the adsorption of diiodooctadecanol, forming a chiral monolayer from a racemic mixture without enantiomer segregation on the surface. An achiral anhydride molecule is found to form two-dimensional enantiomer domains with opposite chiralities. Quasi-phase separation and chiral pairing has been observed for self-assembled monolayers of the iodination products of oleic and elaidic acid. The resulting structures are patterned on a nanometer length scale, in a reproducible and predictable fashion. Mixed monolayers of long-chain alkanoic acids and substituted isophthalic acids have been observed to form stable nanometer scaled meshes on the graphite surface. The structures are controlled by weak interactions between molecules. A balance between hydrogen bonding and van der Waals interactions between the adsorbate molecules and the molecule and substrate control these structures. The structures that result when substituted alkanes are adsorbed on graphite can be used to gain insight into this balance of interactions. By examining a range of long chain substituted hydrocarbon monolayers on graphite using STM, general principles for the formation of chiral overlayers and nano-structured overlayers can be deduced.

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