Corrosion Behaviors on Polycrystalline Gold Substrates in Self‐Assembled Processes of Alkanethiol Monolayers

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Abstract
The adsorption response behaviors with n‐alkanethiol self‐assembled monolayers (SAMs) formed on the surface of polycrystalline gold grains have been investigated in nitrogen and oxygen saturated tetrahydrofuran (THF) solutions by using in situ quartz crystal microbalance (QCM) and atomic force microscopy (AFM). Comparing with frequency‐decreased process in the nitrogen saturated solution, the response behavior shows a frequency increased process in the oxygen saturated solution, indicating that the gold corrosion is accompanied to occur in the self‐assembled process of organothiol that is due to the thiol induction and oxygen oxidation. In the presence of thiol and oxygen, the corrosion effect is stronger than the adsorption effect of organothiols, such as n‐dodecanethiol molecules on gold, which causes gold loss from the QCM surface, made evident from the observation of many corrosive defects or holes produced on the surface of gold grains by AFM image. Furthermore, the kinetic behavior on the corrosion rate of gold dissolved in the organothiol solution with time has been examined. The maximum quantity of gold dissolved into the thiol solution can be calculated to be approximately 8.7×1013 Au atoms cm−2 from the QCM data during the strong corrosion process in the oxygen saturated solution. The corresponding gold corrosion rates at fast and slow stages can be estimated to be 9.2×1011 and 5.4×1010 Au atoms cm−2 s−1, respectively. The surface coverage of SAMs increases from 3.2 to 31.2%, while the gold loss decreases from about 6 to 0.6% of an Au monolayer in the self‐assembled process.