AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP7
Electrochemical Scanning Tunneling Microscopy of Copper Adlayers on Iodine-Covered Au(111) in Sulfuric Acid Solution

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: J. Valenzuela-Benavides, CCMC-UNAM, Mexico
Authors: A. Martinez-Ruiz, CICESE & Fac. de Ciencias, UABC, MEXICO
J. Valenzuela-Benavides, CCMC-UNAM, Mexico
L. Morales de la Garza, CCMC-UNAM, Mexico
N. Batina, UAM-Iztapalapa, Mexico
F. Castillon, CCMC-UNAM, Mexico
Correspondent: Click to Email
We present structural and electrochemical studies of copper electrodeposition on the Au(111) surface precovered with iodine in a sulfuric acid solution. In situ electrochemical scanning tunneling microscopy (STM) studies reveal different adlayer structures depending on the potential of the gold working electrode. Before initiating the underpotential deposition (UPD) of copper, a (5x@sr@3) structure of the iodine adlayer is observed on wide terraces as reported in a similar study with perchloric acid solution. For more negative potentials, the (5x@sr@3) structure transforms to a (3x3) structure around 320mV (vs a Cu/Cu@super ++@ electrode). Cyclic voltammetry (CV) suggests that not enough copper is depositing at this potential to cause the observed (3x3) structure to form, since only a significant ammount of copper deposition begins at potentials below 250mV. This is in sharp contrast to the reported study performed in perchloric acid solution, where the (3x3) is attributed to the UPD of copper of approximately less than half of a monolayer. At the end of the UPD process a (@sr@3x@sr@3)R30@super o@ structure is observed. All these structures are also observed during the CV anodic cycle, returning to the initial (5x@sr@3) structure of the iodine adlayer, which can be removed at a more positive potential with the iodine atoms diffusing into the solution, leaving a bare Au(111) surface. The above results strongly indicate that the stable iodine layer exist on the top layers of Cu and Au during deposition and stripping of Cu. The presence of anions is discussed which may explain the difference between the CV data and the STM images.