Au(111) single-crystal substrates were used in studies of Cu nanofilm formation by electrochemical atomic layer deposion (ALD). Cu undepotential deposition (UPD) was used to deposit the first Cu atomic layer on a Au(111) substrate, modified with an atomic layer of I atoms. By definition, Cu UPD results in the formation of an atomic layer, thus, to deposit subsequent Cu, surface-limited redox replacement (SLRR) was used. The SLRR involved initial formation of Pb UPD on the Cu-coated surface just described. This Pb UPD-coated surface was then exposed to CuSO4 at open-circuit potential (OCP), where the Pb atoms were exchanged for Cu. In the ultrahigh-vacuum electrochemical (UHV-EC) studies presented here, two Pb UPD potentials were investigated: -0.400 and -0.440 V. UHV-EC studies involved use of a surface analysis instrument with optics for low-energy electron diffraction and Auger, and to which was attached an ante-chamber containing a Pyrex glass electrochemical H-cell. In this way, surface analysis was performed without transfer of the deposit through air and the contamination which would result. In addition, studies of the first few cycles of redox replacement were investigated using electrochemical in situ scanning tunnel microscopy (STM), with a flow cell for solution exchange to prevent loss of potential control. (c) 2007 The Electrochemical Society.