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Characterization of the gold/sulphur interface in SAMs of thiols on Au(111)
Self-Assembled Monolayers (SAMs) of thiols on metal surfaces are ubiquitous in the field of nanoscience with potential applications ranging from molecular electronics to biomembranes and nanopatterning. Yet, despite significant efforts, the structure of these systems is still debated.
Contraddictory results are obtained even for the prototypical case of methylthiolate (MT), CH3S, adsorbed on the Au(111) crystal surface. While theoretical simulations have proposed a bridge onding site for the S atom of MT adsorbed on a flat Au(111) terrace, the most recent experimental investigations by Photoelectron Diffraction (PED) and Normal Incidence X-ray Standing Waves (NIXSW)suggest a preference for the ontop site. |
Simulations have shown that vacancies can enhance the adsorption energy of thio-lates. The presence of these defects introduces new possibilities for resolving the controversy around the interface structure, but also new difficulties because of the increased number of degrees of freedom.
Given the hypothesis of a restructuring of the Au- thiolate interface, we decided to employ Density Functional Theory (DFT)-based molecular dynamics (MD) calculations to determine a realistic structural model, from which to fit our experimental data obtained using PED and Grazing Incidence X-Ray Diffraction (GXRD). The model we arrive at in this way contains a certain amount of disorder but resolves the theory-experiment discrepancy that has been prominent in the literature and suggests that the well known formation of superlattices may be a result of an ordering among binding sites and vacancies. In general, our results underscore the importance of disorder at molecule/metal interfaces. At present we are examining the case of chais with 6 and 10 carbon atoms to conferm of contraddict the hypohtesis discussed above.
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Retrieve articlesStructure of a CH3S monolayer on Au(111) solved by the interplay between molecular dynamics calculations and diffraction measurements, Mazzarello, R., Cossaro, A., Verdini, A., Rousseau, R., Casalis, L., Danisman, M.F., Floreano, L., Scandolo, S., Morgante, A., Scoles, G., Physical Review Letters 98, 016102 (2007)
X-ray diffraction and computation yield the structure of alkanethiols on gold(111), Cossaro, A., Mazzarello, R., Rousseau, R., Casalis, L.,Verdini, A., Kohlmeyer, A., Floreano, L. , Scandolo, S., Morgante, A., Klein, M.L., Scoles, G., Science 321, 943 (2008) |
