Gold-thiol monolayers defects

Electron transfer to the perfect blocked electrode is also possible due to electron tunneling, and gold-thiol monolayers provide a unique opportunity to study this phenomenon. Miller and coworkers showed that the level of defects in the monolayers of m-hydroxyalkanethiols of medium chain length (6 < n < 18) has only a minor contribution to the electron transfer, and they performed detailed studies of the electron tunneling in this system367-369. 

Whitesides and coworkers developed a procedure to estimate the density of defects in gold-thiol monolayers. The monolayer surface is exposed to the gold-etching solution, the pits obtained are transferred into pits on the Si surface through further chemical treatment and the number of pits per unit area counted. Long-chain alkanethiolate monolayers prepared by the standard technique show pit densities of ca 100 pits mm . The number of pits sharply increase if the gold surface is stored for a long time in air prior to monolayer deposition . 

Jadzinsky PD, Calero G, Ackerson CJ, Bushnell DA, Komberg RD (2007) Stmcture of a thiol monolayer-protected gold nanoparticle at 1.1 A resolution. Science 318 430-433 Jenkins MW (1977) A new preferential etch for defects in silicon crystals. J Electrochem Soc 124 757-762... 

The monolayers are not perfectly ordered intermolecular voids are present and, therefore, no efficient inhibition of electron transfer across such layers was seen, as reported by Kaifer et al. [36]. There have been several approaches to the provision of anchoring groups of thiol, sulfide, and disulfide functionalities with which CyDs would be deposited on the gold surface as a better ordered monolayer. In the case of j5-CyD, full substitution of the seven primary hydroxyl groups by thiol- or sulfide-containing groups results in submonolayers with relatively large defect sites [36]. 

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