In situ STM study of Cu(111) surface structure and corrosion in pure and benzotriazole-containing sulfuric acid solution

We present results of an in situ STM study on the surface structure and ano dic 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 inhi bitior effects. The initial stages of Cu dissolution as well as the adsorpt ion of BTAH are pronouncedly influenced by the presence of the ordered sulf ate adlayer, which forms in the double layer potential regime and induces a reconstruction of the underlying Cu surface layer, together with a reorien tation of the steps along the close-packed lattice directions. Cu dissoluti on in pure H2SO4 solution proceeds by a step flow mechanism. The onset of d issolution is critically affected by the relative orientation of the sulfat e adlayer on the lower terrace side, with the stability being highest for s teps 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 limita tions, a well-ordered reconstruction has not yet reformed. BTAH adsorption is only observed in the potential regime of the ordered sulfate adlayer. Th e BTAH adlayer is highly defective, which is attributed to the removal of t he reconstruction due to sulfate adlayer displacement. Islands with poorly ordered 1D chain structures are surrounded by areas with no resolved struct ure. Cu dissolution inhibition is manifested by an anodic shift in the onse t 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, sm oothening of the surface is observed with a rate that increases strongly wi th decreasing potential.