Transient adsorption of sulfate ions during copper electrodeposition

Surface-enhanced Raman scattering (SERS) spectroelectrochemical investigations have been carried out in real time on the electrodeposition of copper from sulfuric acid solutions. Sulfate spectra were observed during copper deposition, but not on a copper surface at the same potential in the absence of copper ions in solution. This indicated that sulfate adsorption is a transient process associated with metal deposition. The sulfate band was blue shifted by 11 cm(-1) from its position in spectra from copper(II) sulfate or sulfuric acid solutions, and only the symmetrical stretching vibration band was observed. Chloride displaced sulfate when trace amounts of this halide were also present in solution. Nitrate ions were found to be specifically adsorbed on copper surfaces in nitric acid solutions. When copper ions were present at the interface, a nitrate stretch band, blue shifted by 14 cm(-1), was also observed and this is assigned to adsorption on freshly deposited copper. SERS investigations of copper electrodes in the presence of thiourea confirmed previously reported findings. (C) 2004 The Electrochemical Society.