Domains and Superlattices in Self-Assembled Monolayers of Long-Chain Molecules

Abstract

Self-assembled monolayers (SAMs) are made up of long-chain molecules chemisorbed to a solid substrate.^1,2 Pioneering investigations into fabrication methods and properties of these films^1–10 have generated optimism that they may provide a practical and versatile means of creating chemically tailored surfaces. Such techniques could be used, for example, to facilitate the design of surface properties for applications such as coatings or optical devices, or as substrates for basic research involving wetting¹¹, adhesion, lubrication or biomolecules¹². This potential usefulness is, in part, due to the chemisorption of the headgroups which results in films which are more robust and possibly more well characterized than, for example, the physisorbed Langmuir-Blodgett monolayers. Alkylthiol molecules with a variety of headgroups, S(CH2)_nX, have been used to form uniform, close packed and highly oriented self-assembled monolayers on gold substrates.^3–10 Because the molecules are oriented, with the sulfur headgroup bound to the gold surface, the chemical characteristics of the exposed surface are dominated by the properties of the substituted tailgroup. There appear to be few defects detectable to electrochemical and wetting experiments,^13,4 however, as the structures of even the simplest of these layers are probed in more detail, fairly small domains sizes, superlattice structures, and other types of nonuniformities have been reported.^14,15