Accession Number:

ADA257347

Title:

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

Descriptive Note:

Technical rept.

Corporate Author:

PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY

Personal Author(s):

Report Date:

1992-10-01

Pagination or Media Count:

35.0

Abstract:

In-situ atomic-resolution scanning tunneling microscopy STM has been utilized on ordered Aulll 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 check3 x check3 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 check3 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.

Subject Categories:

  • Physical Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE