Electrolytic metal deposition onto chemically modified electrodes

Some general features concerning electrochemical metal deposition onto elec trodes modified with self-assembled monolayers (SAMs) of alkanethiols are d iscussed. Although thiols of various chain length are briefly addressed, sp ecial emphasis is placed on copper deposition onto an ethanethiol (C2)-modi fied Au(lll) surface. The short alkanethiol blocks the surface to a great e xtent but does not completely suppress charge transfer. We have used in sit u scanning tunneling microscopy (STM) and cyclic voltammetry (CV) to charac terize the structure and the electrochemical behavior of the C2 monolayer i n sulfuric acid electrolyte before and after introducing copper ions to the system. The C2 adlayer consists of domains of two different ordered struct ures. It is shown that the adlayer undergoes a reversible order-disorder tr ansition at potentials slightly negative of 0 V vs. SCE, which testifies to a surprisingly high mobility of the C2 molecules within the SAM. Copper de position on C2-modified gold electrodes shows significant differences from the same process on the bare electrode. A sharp cathodic peak at -0.18V vs. SCE is ascribed to the insertion of a Cu monolayer between Au and the orga nic adlayer. At low overpotentials the Cu deposit exhibits a ramified monat omic high morphology, if the ethanethiol adlayer is dense. Three dimensiona l growth starts at large substrate defects.