Electrolytic metal deposition onto chemically modified electrodes

Some general features concerning electrochemical metal deposition onto electrodes modified with self-assembled monolayers (SAMs) of alkanethiols are discussed. Although thiols of various chain length are briefly addressed, special emphasis is placed on copper deposition onto an ethanethiol (C2)-modified Au(111) surface. The short alkanethiol blocks the surface to a great extent but does not completely suppress charge transfer. We have used in situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) to characterize the structure and the electrochemical behavior of the C2 monolayer in sulfuric acid electrolyte before and after introducing copper ions to the system. The C2 adlayer consists of domains of two different ordered structures. It is shown that the adlayer undergoes a reversible order–disorder transition at potentials slightly negative of 0 V vs. SCE, which testifies to a surprisingly high mobility of the C2 molecules within the SAM. Copper deposition on C2-modified gold electrodes shows significant differences from the same process on the bare electrode. A sharp cathodic peak at -0.18 V vs. SCE is ascribed to the insertion of a Cu monolayer between Au and the organic adlayer. At low overpotentials the Cu deposit exhibits a ramified monatomic high morphology, if the ethanethiol adlayer is dense. Three-dimensional growth starts at large substrate defects. Received: 2 May 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999