Probing Redox-Induced Molecular Transformations by Atomic-Resolution Scanning Tunneling Microscopy: Iodide Adsorption and Electrooxidation on Au(111) in Aqueous Solution

Abstract

In-situ atomic-resolution scanning tunneling microscopy (STM) has been utilized on ordered Au(lll) under electrode potential control in acidic aqueous solution to examine iodine adlayer structures formed by iodide electrooxidation as well as electrosorption. In the potential region, -0. 3 to 0. 4 V vs SCE, below where electrooxidation of solution iodide occurs, several distinct iodine adlayer structures were observed. At the most negative potentials, structures close to the hexagonal ((check)3 x (check)3) R30 deg (Theta = 0.33) pattern are evident. The registry between the adlayer and the substrate lattice was deduced in part from composite domain images created by stepping the electrode potential so to alter markedly the adsorbate coverage during acquisition of a given STM image. At potentials between -0.2 and 0.2 V, adlayer patterns closer to the (5 x (check)3) (Theta = 0.4) structure became increasingly prevalent. This features a diminution in the iodine spacing along two of the three iodine rows, with a corresponding ca 5 deg shift from the R30 deg direction. Above 0.2 V, the STM images indicated the predominant presence of a more complex higher-coverage adlayer (Theta = 0.44) featuring long-range (19+/-lA) Z corrugations rotated by 8-10 deg from the hexagonal iodine adlattice. These corrugations arise from periodic alterations in the iodine binding site, necessitated by I-I distances that approach the van der Waals diameter. Above 0. 3 V, however, poly-iodide chains were also observed, featuring shorter (2.8 - 3. 2 A) I-I distances compatible with adsorbate-adsorbate chemical bonding; these increasingly distort the monomeric iodine superlattice structure.

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Document Details

Document Type
Technical Report
Publication Date
Oct 01, 1992
Accession Number
ADA257347

Entities

People

  • Michael J. Weaver
  • Xiaoping Gao

Organizations

  • Purdue University

Tags

Communities of Interest

  • Materials and Manufacturing Processes

DTIC Thesaurus Topics

  • Acquisition
  • Adsorbates
  • Adsorption
  • Aqueous Solutions
  • Cells
  • Charge Transfer
  • Chemistry
  • Composite Materials
  • Diffraction
  • Distortion
  • Electrochemistry
  • Electrodes
  • Periodic Variations
  • Spectra
  • Substrates
  • Two Dimensional
  • Valence Bond Theory

Fields of Study

  • Chemistry

Readers

  • Electrochemical Surface Science
  • Materials Science and Engineering.

Technology Areas

  • Space