Modification of a Au(111) electrode with ethanethiol. 1. Adlayer structureand electrochemistry

We have used in-situ scanning tunneling microscopy and cyclic voltammetry t o study self-assembled monolayers of ethanethiol on Au(lll) electrodes. The adlayer was found to consist of domains of two different ordered structure s, one corresponding to a (p x root 3), well-established for other short-ch ain alkanethiols, and the other to an oblique primitive (4 x 3) superstruct ure, not previously reported for nonfunctionalized alkanethiols. At potenti als slightly negative of 0 V vs SCE the adlayer undergoes a structural tran sformation that eventually leads to the formation of small pits and islands on the surface. Electrochemical studies in 0.1 M H2SO4 have revealed that around -0.31 V vs SCE the ethanethiol adlayer is reductively desorbed. Oxid ative desorption of ethanethiol takes place at 1.15 V. The cathodic as well as the anodic desorption of the monolayer was monitored by scanning tunnel ing microscopy.