Formation of Self-Assembled Monolayers

Pale-Grosdemange C, Simon E S, Prime K L and Whitesides G M 1991 Formation of self-assembled monolayers by ohemisorption of derivatives of oligo(ethylene glyool) of struoture FIS(CFl2),, (OCFl2CFl2)meta-OFI on gold J. Am. Chem. Soc. 113 12-20... 

Grosdemange GP, Simon ES, Prime KL, Whitesides GM (1991) Formation of self-assembled monolayers by chemisorption of derivatives of oligo(ethylene glycol) of structure HS (CH2)n(OCH2CH2)mOH on gold. J Am Chem Soc 113 12-20... 

Thus, the adsorption of phosphonate or phosphate bearing long alkyl chains (typically from 8 to 18 C atoms) on metal oxide or metal surfaces leads to the formation of self-assembled monolayers (Fig. 13) [121, 127, 131, 132, 135, 150, 154, 174]. 

In 1980 Sagiv [357] pioneered the use of octadecyltrichlorosilane, hereafter referred to as OTS, in the formation of self-assembled monolayers. Subsequently Netzer and Sagiv [17] extended the use of this type of material to the formation of multilayers and this work will be discussed in Section 6.5. 

Figure 6.1. The use of OTS in the formation of self-assembled monolayers. The successive processes which take place are (1) hydrolysis, (2) adsorption and (3) polymerisation with the elimination of water. Further details are given in the text.

Figure 6.2. Trichlorosilanes containing an aromatic group which have been used for the formation of self-assembled monolayers.

FI1R methods were used to study the kinetics of formation of self-assembled monolayers of n-alkanoic acids by adsorption from solutions. 

Although the above discussion is centered on the synthesis of polymeric osmium and ruthenium complexes, the methods employed are also very successful in the preparation of mononuclear complexes. In this context, the preparation of ruthenium or osmium complexes which are suitable for the formation of self-assembled monolayers (see Section 4.3 above) can be prepared by using the same approach. Starting from the precursor [M(bpy)2Cl2], one chloride atom can be replaced to yield complexes of the type [M(bpy)2Cl L]+, where L is the surface active ligand. In the presence of water, species of the type [M(bpy)2(L)2]2+ are obtained. 

The formation of self-assembled monolayers is a powerful tool for surface modification, and it is useful when we need to control surface hydrophilic-ity or prepare fimctional electrodes, for example. Surface modification with belts composed of monolayers of various hydrophihcities can yield surfaces with hydrophilicity gradients. liquid droplets can move across such surfaces against gravity due to favorable interactions with the monolayer surface (Fig. 4.38). 

The formation of self-assembled monolayer (SAM) of the thiolated nucleic acids on gold provides a very useful platform for the development of DNA sensors (10, 11). However, researchers should pay particular attention to the pretreatment and cleaning of gold electrodes to avoid defects in the SAM. First, the gold electrodes must be sequentially polished using 6 and l-pm... 

Covalent modification of surfaces is, in general, an irreversible process. The formation of self-assembled monolayers and adsorbed layers relies on weaker, non-bonding interactions between the surface and the adsorbing molecules. An advantage of this approach is that the adsorbed molecules often form close-packed arrays at the surface. A disadvantage is that the modified surfaces can be less stable because the interactions with the surface are weaker. 

The formation of self-assembled monolayers (SAMs) on solid surfaces must be clearly distinguished from this case since a part of the spatial information required is provided by the surface. This case can be regarded as directed self-assembly of building blocks, which involves structure-directing additives, for example the solid surface. It is clearly distinct from spontaneous self-assembly and can rather be thought of being closely related to a template-assisted process. This may be rationalized by the pattern formation of a molecular layer on different surface orientations of the same material, which leads us to the concept of template-assisted assembly. 

Although the self-assembly of nanoparticles on appropriate substrates is, without doubt, the simplest way to produce monolayers, the method suffers from several disadvantages, mainly that little or no influence can be exerted on the structure and extension of the monolayers. The formation of self assembled monolayers (SAMs) depends on experimental conditions, making reproducibflity difficult. Nevertheless, many quite impressive 2-D structures of metal nanopartides have become known during the course of the past decade. 

Saga, Y. and H. Tamiaki (2004). Facile synthesis of chlorophyll analog possessing a disulfide bond and formation of self-assembled monolayer on gold surface. J. Pho-tochem. Photobiol. B 73(1-2), 29-34. 

Organosulfur compounds have been widely investigated among compounds of interest for the formation of self-assembled monolayers on gold [57]. The latter are relevant for a number of applications such as biosensing, nanopatterning and molecular electronic devices. The study of fundamental processes in the formation of SAMNs of organosulfur compounds is of primary importance to realize functional molecular layers. 

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