Self-assembled alkanethiol monolayers on gold surfaces: resolving the complex structure at the interface by STM

Abstract

The surface properties of metals and metal oxides can be modified by adding a single layer of organic molecules. A most popular route for depositing such a molecular layer is via the formation of self-assembled monolayers (SAMs). The molecules that form SAMs have a functionality which binds to the surface and the adsorption is self-regulated to terminate at exactly one single molecular layer. The very first example, which has become the most widely studied system, of SAMs on metal surfaces consists of chemisorbed alkylthiolate on gold. Despite the simplicity in the preparation of alkanethiol SAMs and the seemingly straightforward structure of such SAMs, the detailed bonding between the sulfur head group and gold is still subject to debate. Experimental and theoretical effort in the last six years has led to a much improved understanding of this classical system of SAMs. In this review, we will highlight the most recent progress in the study of the interfacial structure of alkanethiol SAMs on gold. We focus on the important phenomenon of phase transition that occurs from n-propanethiol to n-butanethiol, and propose a unified structural model to explain how the (3 × 4) phase for short chain alkanethiol monolayers (methyl-, ethyl- and propylthiolate monolayers) changes into the (3 × 2√3)-rect./c(4 × 2) phase for long chain molecular monolayers.

Bicomponent Supramolecular Architectures at the Vacuum–Solid Interface

“…The strong covalent bond between the sulfur atom and the gold surface does not prevent high diffusion, giving rise to well-documented organosulfur/Au(111) self-assembled monolayer systems. 12, 244 In contrast, when the bonding energy is of the same order of magnitude as the diffusion energy, the adsorbate behavior on the surface is more sensitive to temperature effects, and an equilibrium exists between a 2D gas phase on the surface and the gas phase itself. Although surface diffusion of atoms and of small molecules, such as carbon monoxide, is well understood (and often follows a simple single particle hopping model), the problem is significantly more complex in the case of larger molecules 245 because they span several surface adsorption sites, 246 deform during diffusion, 247 interact with surface defects, 248 can induce local surface reconstruction (see below), 249 can diffuse only in specific directions, 250 and can be immobilized or highly mobile depending on the orientation with respect to the surface atomic lattice, 251 among other effects.…”

Dye aggregation identified by vibrational coupling using 2D IR spectroscopy

“…13 Many molecules dimerize on surfaces even at low coverages, as have been studied with STM on single crystal and gold surfaces. [24][25][26][27][28] It is much more difficult to identify dye aggregation on polycrystalline surfaces. In principle, dye aggregation should shift or broaden the UV-Vis spectra, but UV-Vis absorptions of these dyes are so broad that it can be difficult to recognize aggregation or the size of aggregates as compared to other effects that shift and broaden the absorption spectrum.…”

Probing molecular mechanisms of M13 bacteriophage adhesion

“…The gold layers were attached to the curved surfaces of cylindrical glass discs (Radius, R 2 cm) by painting them with an optical adhesive, Norland optical adhesive 81 (Norland Products, Inc. Cranbury, NJ, USA), and subsequently UV treating the samples for 40-60 min. The discs with gold-coated top surfaces were immersed into 1 mM alkanethiol-ethanol solution for the formation of SAM structure via gold-sulfur bonds on the gold (111) surfaces 43 . After 16-18 h, the discs were sonicated for 30 s, washed with ethanol, and dried by nitrogen gas to remove physical impurities and excess SAM molecules from the surfaces.…”