Non-contact mode atomic force microscopy is used to investigate the protective film formed by benzotriazole (BTAH) on a Cu(111) surface in acidic solution under potential control. The amount of film growth as determined by AFM correlates well with that determined electrochemically. The AFM images indicate that the Cu-BTA film is highly heterogeneous relating to the amount of BTA available at the surface. Less concentrated BTA solution yields less uniform films. After the reduction of the film, the Cu surface roughness increases slightly due to the restricted diffusion of Cu species through the Cu-BTA film during Cu reduction. (c) 2006 Elsevier B.V. All rights reserved.