Modification of a Au(111) electrode with ethanethiol. 2. Copper electrodeposition

Copper electrodeposition from sulfuric acid solutions onto ethanethiol-modi fied Au(lll) electrodes was studied by in-situ scanning tunneling microscop y and cyclic voltammetry. The ethanethiol adlayer undergoes an order-disord er transition before Cu underpotential deposition starts around +0.20 V ver sus SCE. Five percent of a monolayer is deposited positive of the Nernst po tential at a sweep rate of 10 mV s(-1). At low overpotentials the Cu deposi t exhibits a ramified monatomic high morphology, if the ethanethiol adlayer is dense. In all cases three-dimensional growth nucleating at large substr ate defects is found in addition. Cyclic voltammetry revealed two character istic de position features: firstly, a sharp cathodic peak at -0.18 V which is ascribed to the insertion of a Cu monolayer between Au and the organic adlayer and, secondly, a current loop due to Cu bulk deposition. The corres ponding stripping peaks are found at 0.08 and 0.35 V, respectively.