Cyclic voltammetry, current-time-transient measurements. and X-ray photoelectron spectroscopy (XPS) have been used to study the nucleation behavior of electrochemically deposited Cu films on Ru Substrates as a function of Ru pre-treatment. Pre-treatment consisted of cathodic polarization in either 1M H2SO4 or in 1 M H2SO4 + 1 mM KI, followed by sample emersion and placement in a 1 M H2SO4 + 50 mM CuSO4 plating bath. XPS measurements confirmed the presence of adsorbed I on the Ru surface following pretreatment in the KI/H2SO4 solution. Cyclic voltammogram (CV) data for electrodes either as-received OF pre-reduced in H2SO4 and then immersed in the plating solution exhibited a broad peak in the overpotential region consistent with oxide reduction followed by Cu deposition. No underpotential deposition (UPD) feature was observed for these electrodes. In contrast, the sample pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD Cu feature centered at 80 mV vs. Ag/AgCl. Current-time-transient (07) measurements of Cu deposition on as-received electrodes or electrodes pre-reduced in I-free solution exhibited potential-independent kinetics that are not well described by either progressive or instantaneous nucleation models and which at long times indicate a combination of diffusion and kinetic control. In contrast, M measurements of deposition kinetics for samples reduced in I-containing electrolyte exhibited complex, potential-dependent behavior and that at long times indicates diffusion control. XPS results also indicated that the iodine adlayer on Ru reduced in I-containing electrolyte is stable upon polarization to at least -200 mV vs. Ag/AgCl. These data indicate that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. Therefore, electrochemical pre-treatment in I-containing electrolyte may be of practical utility tinder industrial conditions for Cu electroplating. (C) 2009 Elsevier Ltd. All rights reserved.