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Spectroelectrochemical characterization of ultrathin organic films deposited on electrode surfaces Casanova Moreno, Jannu Ricardo


Thin organic layers deposited on electrodes are ubiquitously proposed for a variety of surface-related applications. The quality of these layers is usually assessed by analytical methods that average the measured signal over a large area compared to the molecular scale. This work outlines the use of in-situ fluorescence microscopy as a characterization method by analyzing three examples of such layers. First, a heterogeneous Langmuir layer was physically adsorbed to a gold electrode via the Langmuir-Schaefer method and the effects of the substrate analyzed by comparing the adsorbed layer with the predecessor floating film. Through the use of a dimer-forming fluorophore, substrate mediated condensation was suggested. Second, the reductive desorption of self-assembled monolayers (SAMs) from microelectrodes was used to investigate the movement of the released thiolate molecules. Once in solution, these molecules were found to follow a buoyant movement, consequence of the high local concentration of H₂ resulting from the simultaneous reduction of water under the conditions employed. Finally, a DNA SAM system that has been previously suggested as a biosensing platform was investigated for heterogeneity. It was found that the substrate crystallography had a significant effect on the density and efficiency of potential driven change in conformation of the immobilized probes. Furthermore, a deconvolution method is proposed in order to correct for the effect of the electrode charging time constant on the measurements of the kinetics of the DNA conformation change. Overall, the performed experiments show that in-situ fluorescence microscopy is a useful technique to analyze distance dependent phenomena involving these deposited layers. Moreover, the coupling between electrochemistry and fluorescence allows not only to monitor but also to drive changes in the layers, creating systems capable of studying the dynamics of the deposited films. The inclusion of the proposed technique as a characterization tool during the development of systems based on ultrathin organic films could improve the understanding of the influence of the deposition conditions on the film quality, helping to attain the necessary robustness to make the proposed systems actually achieve their proposed applications. Supplementary video material is available at: http://hdl.handle.net/2429/51003

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