Highly ordered adsorbate structures on Cu(111) in the potential regime of hydrogen evolution - An In-situ Stm Study

The potential-dependent atomic structures of a Cu(I 11) electrode surface exposed to dilute sulfuric acid have been studied by means of in-situ STM. At a positive electrode polarization the specific adsorption of sulfate anions induce a reconstruction of the copper substrate characterized by an expansion of the topmost substrate layer. A direct proof for the adsorbate-induced reconstruction is given by a kind of spectroscopic STM measurement where not only the adsorbate but also the underlying reconstructed copper substrate is imaged. Sweeping the potential in negative direction sulfate desorbs from the surface accompanied by the lifting of the reconstruction. The bare copper surface, however, does not remain stable under these conditions. An adsorption of solvent species takes place leading to the formation of a highly ordered, hexagonal Moire pattern which undergoes an electrocompression process starting with a c(4 x 4) and ending with a c(5 x 5) superstructure with decreasing potentials. These adsorbate layers remain stable even under massive hydrogen evolution. The dependence of the imaging properties of this adlayer on the tunneling conditions has been systematically studied.