Gold-sulphur interaction

In the formation of SAMs, the film-forming molecules order themselves by chemical interaction with neighbouring molecules and with the substrate surface. This technique has been applied for a large variety of modifier/substrate combinations. Various sulphur compounds, like alkanethiols and (di)sulfides have been deposited on metals such as silver, copper and gold isocyanides on platinum and carboxylic acids on aluminum oxide and silver oxide.75 Alkyltrichlorosilanes have been deposited on gold, mica, aluminum, tin oxide and silicon oxide. The latter combination is of interest here. 

REPULSIVE INTERACTIONS BETWEEN GOLD AND SULPHUR ON TRANSITION METAL SURFACES... 

Repulsive interactions between gold and sulphur on transition metal surfaces 467... 

Electron transfer cannot occur in blocking films. However, for very thin self-assembled monolayers (SAMs] of alkane thiols or oxide films, electrons can tunnel through the film and cause Faradaic reactions. Monolayer of alkane thiols can form spontaneously ordered adlayers on substrate like Au(lll] due to a strong interaction between the sulphur of the thiol and the gold substrate. These SAMs have received tremendous attention in recent years [209,210]. 

In order to organize molecules on a gold surface it is possible to prepare a derivative of the molecule with a functional group containing sulphur, which should interact covalently with the surface anchoring the molecule. In terms of strength... 

Figure 16.22 Ferrocene covalently linked to an alkanethiol adsorbed to the surface of a gold electrode. The ferrocene-substitnted alkylthiol is diluted in other alkanetfaiols to minimise the interactions between ferrocenes and favour a homogenous coverage of the electrode. The stability of the monolayer is due to the strong adsorption of the sulphur atom at the surface of the gold electrode.

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