Determination of the potential of zero charge of Au(1 1 1) electrodes modified with thiol self-assembled monolayers using a potential-controlled sessile drop method

The potential of zero charge (pzc) of the thiol-modified Au(1 1 1) electrode has been determined for self-assembled monolayers (SAMs) of octadecanethiolate (ODT), undecanethiolate (UDT), propanethiolate (PT), and 1H,1H,2H,2H-perfluorodecanethiolate (PFDT) by measuring the contact angle of a drop of an aqueous 0.1 mol dm−3 NaClO4 solution on the SAM-covered electrode as a function of the electrode potential. The values of the pzc for ODT, UDT, PT, and PFDT SAMs were −0.52, −0.49. −0.3, and 1.04 V (vs. Ag|AgCl|satd. KCl), respectively. The variation of the values is ascribed to the change in the surface potential on the solution side of the electrode|solution interface due to the difference in the dipole moments of alkanethiolates on Au(1 1 1), which is supported by the ab initio calculation of these thiolates adsorbed on a four-atom cluster of Au atoms.