The reductive desorption of a self-assembled monolayer (SAM) of a fluorescent thiol molecule (BodipyC10SH) from Au was characterized using electrochemistry and epi-fluorescence microscopy. Molecular luminescence is quenched near a metal surface, so fluorescence was only observed for molecules reductively desorbed and then separated from the electrode surface. Fluorescence imaging showed that reductive desorption was selective, with desorption occurring from different regions of the Au electrode depending on the extent of the negative potential excursion. When desorbed, the molecules were sufficiently mobile, diffusing away from the electrode surface, thereby preventing oxidative readsorption. At sufficiently negative desorption potentials, all of the thiol was desorbed from the electrode surface, resulting in fluorescence at the air/solution interface. The selective removal of the thiol monolayer from distinct regions was correlated to features on the electrode surface and was explained through potential-...

Selective reductive desorption of a SAM-coated gold electrode revealed using fluorescence microscopy.

The reductive desorption of cysteine and 4-mercaptobenzoic acid monolayers formed on polycrystalline and single-crystalline gold substrates has been investigated. Three cathodic waves observed at polycrystalline gold electrodes are correlated with reductive desorption from each small domain of the low index faces, i.e. (111), (100) and (110), over the surface. The stability of the adsorbates differs substantially depending on the surface crystallographic orientation, in the order (111) < (100) < (110). Thus, the reductive desorption occurs at certain potentials, leading to an apparent peak separation on their cyclic voltammograms. Partial desorption of the adsorbate via control of the potential would be a simple and reliable method of fabricating functional electrodes designed for use as electrocatalysts or sensors, on which only the small domains of the (111) face could be selectively exposed to an electrolyte.

Multiple voltammetric waves for reductive desorption of cysteine and 4-mercaptobenzoic acid monolayers self-assembled on gold substrates

We have investigated the structure of (3-mercaptopropyl)sulfonate (MPS) monolayer self-assembled onto gold surfaces by quartz crystal microbalance with energy dissipation monitoring (QCM-D) and various electrochemical methods. QCM-D experiments show that the MPS monolayer behaves as a thin rigid film with a surfacic mass of 166 ng cm-2. Interfacial capacitance measurements demonstrate that the MPS monolayer is a rather open structure that can be penetrated by the ionic species of the phosphate buffer electrolyte. From MPS reductive desorption experiments, MPS surface concentration corresponds to 4.6 × 10-10 mol cm-2, which represents 60% of the coverage reported for a densely packed thiol monolayer. Despite this low packing density, oxidation of catechol is strongly inhibited leading to voltammograms that are free of diffusional contribution. This unique behavior has been exploited to show that the MPS monolayer covers the entire gold surface with a surface coverage at least equal to θ = 0.9981, which mea...

Structural characterization of (3-mercaptopropyl)sulfonate monolayer on gold surfaces.

http://sedici.unlp.edu.ar/bitstream/handle/10915/82668/Documento_completo.pdf?sequence=1

The development of metal overlayers with smooth and rough topographies

We show how gold recrystallizes when under the influence of electrochemical potentials. This "cold annealing" occurs without charge transfer reactions and preserves nanoscale structural features. By performing the process on plasmonic nanostructures, grain growth is monitored noninvasively by optical spectroscopy. In this way, the influence from crystal structure on plasmon resonances can be investigated independently. Observed spectral changes are in excellent agreement with analytical models and changes in electron relaxation time and plasma frequency are calculated.

Miguel Ipohorski

Papers

Electrochemical faceting of polycrystalline gold in 1 M H2SO4