The inhibitive effect of benzotriazole on a commercial copper surface (phosphorus-deoxidized copper) was studied by a scanning electrochemical microscope (SECM) in an aqueous sodium sulfate solution using ferrocenemethanol (FcMeOH) as the redox mediator. The formation of the inhibitive film was followed as a function of time and as a function of the potential of the copper substrate. The results were analyzed using the existing models in the literature. The results show that the potential has a crucial effect on the growth of the [Cu(I)-BTA] film. At a potential close to the dissolution range of copper, the surface changes gradually from almost ideally conductive to almost ideally insulating surface in the presence of benzotriazole, but at more negative potentials the effect is diminished and finally deceased. Quartz crystal microbalance experiments showed that the mass of an adsorbed layer must correspond to a multilayer. (C) 2004 The Electrochemical Society.