Atomic structure and tip-induced reconstruction of bromide covered Cu(1 1 0) electrodes

Abstract

The behavior of specifically adsorbed bromide on Cu(1 1 0) in 10 mM HBr has been studied using cyclic voltammetry in combination with high resolution in situ electrochemical scanning tunneling microscopy (EC-STM). At cathodic potentials near the onset of the hydrogen evolution reaction the structure of the bare copper surface was observed by EC-STM. A variation of the electrode potential in positive direction causes a specific anion adsorption leading to the formation of a highly ordered superstructure with a quasi-hexagonal symmetry. The two-dimensional lattice of this adlayer can be described by a c(3 × 2) unit cell. The bromide anions are arranged parallel to the close packed copper rows and are located in three different types of adsorption sites. These inequivalently bound bromide species are imaged with different brightness in the STM-pictures. As a result the bromide adlayer exhibits a long-ranged wavy superstructure superimposed on the atomic corrugation. Tip induced copper corrosion is used to obtain highly ordered nanostructures due to a locally confined electrochemical annealing process proceeding along the [0 0 1]-direction of the substrate. This annealing process results in the formation of Cu(1 0 0)-facets.