Organosulfur compounds, gold surface

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 ...

Nuzzo RG, Zegarski BR, Dubois LH (1987) Fundamental studies of the chemisorption of organosulfur compounds on Au(lll). Implications for molecular self-assembly on gold surfaces. J Am Chem Soc 109 733-740... 

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

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. 

It is well known that organosulfur compounds react with gold surfaces. In 1982 Taniguchi et al. observed the spontaneous formation of pyridine disulfide SAMs on a gold surface [62]. In 1983, Nuzzo and Allara showed that SAMs of alkanethiolate on gold could be prepared by adsorption of n-alkyl disulfides from dilute solutions [63]. This report initiated a rapid growth in SAM research. 

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. 

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