Examination of the electrified interfaces of Au(1 1 1) in 0.1 M HClO4 containing organic iodide compounds with cyclic voltammetry and in situ scanning tunneling microscopy

We used cyclic voltammetry and in situ scanning tunneling microscopy (STM) to examine the adsorption of iodine, iodobenzene, iodoheptane and 1,4-dihydroxy-2-iodobenzene on a well-ordered Au(1 1 1) electrode in 0.1 M HClO4 solutions. The cyclic voltammograms of Au(1 1 1) electrodes modified with a monolayer of each individual iodo-compound all showed two well-defined oxidation features at 1.5 and 1.65 V (vs. reversible hydrogen electrodes), although the intensity of these two peaks vary with adsorbates. STM atomic resolutions of the iodine adatoms reveals a (p×√3) structure at negative potentials and a compressed structure, identified as (7×7)R21°, at positive potentials. Similarly, a (p×√3) structure was observed for the organic iodide molecules with the value of p varying between 2.6 and 2.9. However, they did not rearrange to form the compressed structure at more positive potentials. The voltammetric and STM results indicate that the organic iodide molecules largely decomposed upon their adsorption at Au(1 1 1) electrodes, producing an iodine overlayer and alkyl and aryl organic fragments dissolving in the solutions. This view is borne out from the cleanliness of the surface, showing only well-ordered iodine structures.