Organosulfur monolayers

Ohmic drop, 32, 88, 105, 129 Operational amplifier, 105 Optically transparent electrode, 40 Organic-phase biosensors, 181 Organic solvents, 102 Organosulfur monolayers, 118 Overvoltage, 14, 121 Oxygen, 75, 87, 103, 177, 190, 193... 

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Fig. 11. Surface-active organosulfur compounds that form monolayers on gold (a) alkanethiol (b) dialkyl disulfide (c) dialkyl sulfide (d) alkyl xanthate ...

A rational manipulation of the electrode surface functionality by immobilizing selected types of molecules is an essential key for the development of electrochemical sensors and devices. One of the recent studies in this area has focused on monolayer formation on gold surfaces from organosulfur precursors [11]. Stable attachment of organic molecules to gold... 

Strong L, Whitesides GM (1988) Structures of self-assembled monolayer films of organosulfur compounds adsorbed on gold single crystals electron diffraction studies. Langmuir 4 546-558... 

Maksymovych P, Voznyy O, Dougherty DB, Sorescu Dan DC, Yates JT (2010) Gold adatom as a key structural component in self-assembled monolayers of organosulfur molecules on Au(l 11). Prog Surf Sci 85 206-240... 

Self-Assembled Monolayers and Multilayers Derived from Organosulfur Compounds Chemisorbed on Gold and Other Metals... 

Molecular self-assembly is a technique to form highly ordered, closely packed mono-layers on various substrates via a spontaneous chemisorption process at the interface.11,12 Earlier research done in this field includes the self-assembly of fatty acids monolayers on metal oxides,14,15 SAMs of organosilicon derivatives on metal and semiconductor oxides,16,17 and organosulfur SAMs on metal and semiconductor surfaces.18,19 Among the organosulfur SAMs, the most thoroughly investigated and characterized one is alkanethiol SAM formed on Au(l 11) surfaces.12... 

Poirier, G. E. Characterization of Organosulfur Molecular Monolayers on Au(lll) using Scanning Tunneling Microscopy. Chem. Rev. 97, 1117—1127 (1997). 

In the 1940s, it was demonstrated in the pioneering work of Zisman and coworkers [8] that the LB technique is not the only way to create an organized organic monolayer on a solid substrate. It was demonstrated that when a compatible substrate is exposed to a solution of an amphiphilic compound, the dissolved molecules form a self-assembled monolayer on the substrate surface. Such films maintain their structural integrity after they are removed from solution. The most common examples of such films are organosulfur films on gold substrates [9] and alkyltrichlorosilane films on silicon dioxide substrates [10]. Compared with the LB films, the self-assembled films are somewhat less ordered. On the other hand, these films are easier to prepare, since they do not require special instrumentation and can easily be deposited on both planar and non-planar substrates. Also, in many cases the amphiphilic molecules which make the self-assembled film are chemisorbed on the substrate. Such films are more stable when heated or exposed to solvents than are typical LB films, which are held to the substrate by non-covalent interactions. 

Self-assembled monolayers of organosulfur compounds on gold surfaces... 

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. 

Fig. 9 Surface-active organosulfur compounds that form monolayers on gold [8],...

The original work of Nuzzo and Allara [4] on the use of the strong interaction between gold surfaces and organosulfur compounds for monolayer construction opened the field of SAMs prepared by molecular self-assembly on metal substrates via formation of metal-thiolate (or disulfide or dialkyl sulfide) bonds [15]. The introduction of functional SAMs on metal substrates was a natural development that followed [10, 11]. Owing to the similarity with highly specialized biological membranes, functional SAMs are sometimes called artificial membranes. 

Spontaneously chemisorbed monolayers of organosulfur molecules such as thiols and disulfides on Au electrodes have also been extensively investigated using STM [54]. High-resolution STM images of simple thiols such as 4-mercaptopyridine adsorbed on Au(lll) revealed the internal structures and microorientation of each molecule [55, 56]. Because of publication limitations, this chapter has only focused on in situ STM of simple aromatic molecules. 

Organosulfur compounds represent the most common class of molecules exploited for formation of monolayers. Among the possible systems, the most extensively studied ones are based on thiols adsorbed on Au. 

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