We present results of an in situ STM study on the surface structure and anodic dissolution of Cu(111) electrodes in pure 0.01 M H2SO4 solution and in solution containing the corrosion inhibitor benzotriazole (BTAH), which is aimed at an atomistic understanding of the dissolution process and the inhibitior effects. The initial stages of Cu dissolution as well as the adsorption of BTAH are pronouncedly influenced by the presence of the ordered sulfate adlayer, which forms in the double layer potential regime and induces a reconstruction of the underlying Cu surface layer, together with a reorientation of the steps along the close-packed lattice directions. Cu dissolution in pure H2SO4 solution proceeds by a step flow mechanism. The onset of dissolution is critically affected by the relative orientation of the sulfate adlayer on the lower terrace side, with the stability being highest for steps running perpendicular to the close-packed sulfate rows. The retracting steps often expose apparently disordered areas, which are attributed to a disordered sulfate adlayer on a Cu surface where, because of kinetic limitations, a well-ordered reconstruction has not yet reformed. BTAH adsorption is only observed in the potential regime of the ordered sulfate adlayer. The BTAH adlayer is highly defective, which is attributed to the removal of the reconstruction due to sulfate adlayer displacement. Islands with poorly ordered 1D chain structures are surrounded by areas with no resolved structure. Cu dissolution inhibition is manifested by an anodic shift in the onset of dissolution as well as by the blocking of the step flow etch mechanism, reflecting a stabilization of the Cu steps by adsorbed BTAH. Dissolution at higher potentials proceeds predominantly via formation of monolayer etch pits. When the potential is reversed back into the double layer regime, smoothening of the surface is observed with a rate that increases strongly with decreasing potential.

Atomic-resolution in situ scanning tunneling microscopy (STM) observations of (100) Cu electrodes in H 2 SO 4 solution containing 10 6 to 10 4 M benzotriazole (BTA) are presented. At potentials < -0.6 V vs. a Hg/Hg 2 SO4 (K 2 SO 4 sat.) reference electrode ordered superstructures of a chemisorbed BTA adlayer as well as a disordered, chainlike structure, suggesting a polymerized BTA film, were observed. Cu corrosion commences at potentials < -0.4 V by the formation of monoatomic etch pits and slow step flow etching, resulting in roughening of the Cu surface. On changing the potential back to --0.6 V the surface becomes level again due to redeposition of dissolved Cu at the Cu steps.

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