Adsorption of organic molecules on gold electrodes

作者：Teobaldi Gilberto; Zerbetto Francesco^*

来源：Journal of Physical Chemistry C, 2007, 111(37): 13879-13885.

DOI：10.1021/jp074017g

We develop a simple approach to investigate the stability of an organic adlayer on a gold surface in the presence of an external voltage. All atoms are treated explicitly, and there is no predefined bond connectivity between the metal and the organic phase so that molecules are able to slide on the surface. Three applications are discussed: the first considers the structure and energetics of the deposition of citric acid on Au(111). The second is the similar deposition of a porphyrin derivative. The third is the voltage dependent desorption of thiolate chains in self-assembled monolayers. Consistently, the energetics of the systems are driven by the stabilization of the organic adlayer through the bias-dependent charge transfer between metal and molecules. Comparison with experimental results is encouraging. For case 1, the experimental formation of ordered structures between 0.5 and 0.8 V is explained by an increased stability of the cell of 4 molecules and 512 gold atoms. Analogously, the formation in case 2 of a well-ordered adlayer coincides with a region of high stability of a cell of 2 porphyrins and 672 gold atoms. Finally, in case 3, the estimated experimental slope of the activation energy of desorption, 10.8 kcal mol(-1) V-1, is bracketed by those calculated for the desorption of a thiolate chain from a half-packed and from a fully packed thiolate monolayer and has the opposite sign of the slope for the desorption of an isolated chain. In all cases, the driving force for electroadsorption is the decrease of the molecular charge with voltage, which, in turn, decreases the Coulombic interactions in the organic adlayer.

• 出版日期2007-9-20