Copper plate was observed by atomic force microscopy (AFM) after it was immersed in acid electrolyte with polyethylene glycol (PEG) and chloride ions (Cl-). The AFM image confirmed the existence of adsorbed particles, which are in a flat-cone shape with a bottom radius of 15-25 nm and a height of 2-4 nm. The intermediate complex of copper dissolution/deposition was investigated by means of an electrochemical quartz crystal microbalance through detecting the simultaneous mass change of the electrode during cyclic voltammetric (CV) measurement. The two current peaks in the CV curves illustrate the generation and consumption of intermediate complex Cu+ center dot Cl- center dot PEG on the copper electrode. (C) 2004 The Electrochemical Society.