SAMs of alkanethiolates on gold

SAMs of alkanethiols on gold are the by far the most studied systems. For detailed descriptions of their growth and structural features, the recent reviews by F. Schreiber [4] and D. K. Schwarz [33] are highly recommended. It is believed that the thiol reacts with the gold substrate according to the following equation [5] ... 

Formation of SAMs SAMs of alkanethiolates on gold ean be easily prepared by spontaneous adsorption of alkanethiols onto gold, either from solution or vapor phase. Although it is generally accepted that the reaction involved can be expressed as (2),... 

Figure 8 Schematic illustration for the formation of SAMs of alkanethiolates on gold [73], (A) Alkanethiols adopt the highly mobile lattice-gas phase (B) above a critical value of coverage, striped-phase islands are formed (C) surface reaches saturation coverage of striped phase (D) surface undergoes lateral-pressure-induced solid phase transition high-density islands nucleate and grow at domain boundaries (E) high-density islands grow at the expense of the striped phase until the surface reaches saturation...

As discussed earlier, SAMs of alkanethiols on gold surfaces offer access to highly ordered, surface-confined molecular structures. The use of these assemblies as stable, well-defined spacers for studies of electron transfer between the gold electrode and redox eenters attached to the film surface [50, 73-83] or in solution [44, 46, 84] is depicted in Figure 5. The densely packed monolayer maintains a precise separation between a gold electrode surface and the pendant or dissolved redox center, and effectively eliminates conformational mobility that can complicate electron-transfer rate studies [73]. An advantage of using electrode-confined spacers is that... 

Self assembled monolayers (SAMs) have aroused wide spread interest as they provide an opportunity to define the chemical functionality of surfaces with molecular precision, thus creating potential applications related to the control of wettability, biocompatibility and the corrosion resistance of surfaces of a wide range of materials II), Two families of SAMs have received the most attention, SAMs of alkanethiols on gold and alkylsilanes on silicon. 

Applications of Self-Assembled Monolayers (SAMs) of Alkanethiolates on Gold... 

Investigations concerning preparation, mechanism [16], characterization, and properties of SAMs have been reviewed before [9,17-19]. We will focus on the applications of SAMs of alkanethiolates on gold, emphasizing the recent developments of the last 2-3 years. Some of these advances are extensions of older work that is reviewed elsewhere. This chapter summarizes recent progress in the following areas ... 

Self-assembled monolayers (SAMs) of alkanethiolates on gold have been studied more and more extensively over the last fifteen years with tremendous potential as model systems for all kinds of complex interfaces and as important and practical tools for novel applications such as nanofabrication. SAMs on gold have become foundational systems from which an enormous amount of study has developed concerning a plethora of new, well defined, self-assembled surface interfaces. 

The chemistry and structures of SAMs of alkanethiolates on gold have been extensively studied, and need not be reviewed here [44]. In brief, when fully equilibrated and in their most stable form, these SAMs seem to be two-dimensional quasicrystals, with the sulfur headgroups epitaxial on the gold surface. A 30° tilt of the trans-extended alkane chains brings these chains into van der Waals contact. Functional groups present on the termini of the chains are exposed to the solution. Conformational disorder in the system is concentrated in the terminal regions of the chains. 

Lopez, G. P., Albers, M. W., Schreiber, S. L., Carroll, R., Peralta, E., and Whitesides, G. M. (1993) Convenient methods for patterning the adhesion of mammalian-cells to surfaces using SAMs of alkanethiolates on gold, J. Am. Chem. Soc. 

Molecular self-assembly, the spontaneous formation of molecules into covalently bonded, well-defined, stable structures, is a very important concept in biological systems and has increasingly become the focus of synthetic sophisticated research [56]. In 1946, Zisman published the preparation of a monomolecular layer by adsorption of a surfactant onto a clean metal surface [57]. However, the potential of self-assembly was not recognized at that time, and the techniques for surface analysis were limited, so the development of self-assanbly was slow. In 1980, Sagiv reported SAMs with the adsorption of octadecyltrichlorosilane (OTS-CigHjTSiClj) on a silicon substrate [58]. In 1983, Nuzzo and Allara [59] successfully prepared SAMs of alkanethiolates on gold. As a potential molecular-level lubricant, SAMs have attracted much attention [60-62] and have been demonstrated to be capable of effectively reducing the friction and adhesion in MEMS [3,61,63,64]. 

SAMs of alkanethiolates on gold provide excellent model systems for studies on interfacial phenomena (e.g., wetting, adhesion, lubrication, corrosion, nucleation, protein adsorption, cell attachment, and sensing). These subjects have been reviewed previously [125,183-185]. Here we focus on applications that involve using chemical synthesis of functional SAMs after their assembly. 

Sun and Leggett [66] further demonstrated the use of SNOM to fabricate features 20 nm in size in SAMs of alkanethiols on gold substrates. This additional study established that it is routinely possible to fabricate structures smaller than the SNOM probe aperture and that the dimensions of the written structures correlate with the substrate morphology. Sun and Leggett [66] conclude that non-radiative interactions, possibly plasmonic, between the metallic substrate and the fibre result in a focusing of the electric field beneath the aperture and that this is more pronounced when polycrystalline substrates with comparatively small grain sizes are used. 

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