| Abstract
| - The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM)in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image simulation.Two sets of voltammetric signals are observed. One peak at −(0.65−0.70) V (SCE) is caused by reductivedesorption of cysteamine. The other signal, at −(0.25−0.40) V consists of a peak doublet. The pH dependenceof the latter suggests that the origin is catalytic dihydrogen evolution. The doublet feature is indicative of twodistinct cysteamine configurations. Cysteamine monolayer formation from initial nucleation to a highly orderedphase has been successfully observed in real time using oxygen-free in situ STM. Random cellular patterns,disordered adlayer formation accompanied by high step edge mobility, and ultimately a highly ordered (√3× 4) R30° lattice are observed sequentially. Pits are formed due to enclosure of the mobile edges during theadsorption process. In the highly ordered cysteamine layer, each unit has two spots with apparent 0.6 Åheight difference in STM images. The coverage 5.7 ± 0.1 × 10-10 mol cm-2 determined by voltammetrysupports that the spots represent two individual cysteamine molecules. A priori MD and density functionalsimulations hold other clues to the image interpretation and indicate that the NH3+ groups dominate thetunneling contrast. A wide range of interface structures, showing variations in the sulfur binding site andorientation, gauche and trans conformers, and especially hydrogen-bonding interactions, are examined, fromwhich it is concluded that the adsorbate structure is controlled by interactions with the solvent rather thanwith the substrate.
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