Electrodesorption kinetics and molecular interactions in well-ordered thiol adlayers on Au(111)

The electrodesorption of root 3x root3 R30 degrees thiol and sulfur lattice s on Au(111) has been investigated by in situ STM and electrochemical metho ds. For thiol and sulfur adlayers, the root 3x root3 R30 degrees lattice is desorbed in sharp voltammetric current peaks. The electrodesorption kineti cs involves nucleation and growth of holes. From the analysis of the depend ence of the peak potential (E-p) on the length of the hydrocarbon chain (n) , the thiol-thiol interaction results in approximate to3 kJ mol(-1)/C unit. The value of E-p for n = 0 indicates that the S-Au(111) bond energy in roo t 3x root3 R30 degrees thiol lattices is approximate to 19 kJ mol(-1) small er, and the bond has a lesser ionic character than the S-Au(111) bond in th e root 3x root3 R30 degrees sulfur lattice. Monte Carlo simulations of a de sorption model reproduce well the experimental potentiostatic and potentiod ynamic results for thiol desorption.