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

Abstract

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 (Ep) on the length of the hydrocarbon chain (n), the thiol−thiol interaction results in ≈3 kJ mol-1/C unit. The value of Ep 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.