Electrodesorption Kinetics and Molecular Interactions in Well-Ordered Thiol Adlayers On Au(111)

The electrodesorption of √3×√3 R30° thiol and sulfur lattices on Au(111) has been investigated by in situ STM and electrochemical methods. For thiol and sulfur adlayers, the √3×√3 R30° lattice is desorbed in sharp voltammetric current peaks. The electrodesorption kinetics involves nucleation and growth of holes. From the analysis of the dependence of the peak potential ( E p ) on the length of the hydrocarbon chain ( n ), the thiol−thiol interaction results in ≈3 kJ mol -1 /C unit. The value of E p for n = 0 indicates that the S−Au(111) bond energy in √3×√3 R30° thiol lattices is ≈19 kJ mol -1 smaller, and the bond has a lesser ionic character than the S−Au(111) bond in the √3×√3 R30° sulfur lattice. Monte Carlo simulations of a desorption model reproduce well the experimental potentiostatic and potentiodynamic results for thiol desorption.