IN-SITU STM STUDIES OF CU UNDERPOTENTIAL DEPOSITION ON AU(100) IN THE PRESENCE OF SULFATE AND CHLORIDE ANIONS

The influence of anions on the underpotential deposition of Cu on Au(100) electrode surfaces has been investigated by in situ scanning tunneling microscopy. In pure Cu2+-containing H2SO4 solution a (1×1) lattice is observed in the entire potential range and interpreted in terms of an increasing population of the energetically most favorable lattice sites by mobile Cu adatoms with weakly repulsive interactions. In the presence of Cl- anions a one-dimensionally incommensurate (n×2) structure is formed, coincident with a sharp peak in the current-potential curve. In this structure the adatoms are arranged in a quasihexagonal pattern with a spacing of 3.6 to 4.4, which is close to the diameter of the Cl- ion. The difference in the observed adsorption behavior corresponds well to the different shape of the corresponding electrochemical current-potential curves. © 1995 The American Physical Society.